Vocab v53

Olmecs

(1400 B.C.E. to 500 B.C.E.) earliest known Mexican civilization,lived in rainforests along the Gulf of Mexico, developed calendar and constructed public buildings and temples, carried on trade with other groups.priests/aristocrats were at the top of society, built a ceremonial center, wroshiped the jaguar and werejaguar, best remains are the stone carved heads at la venta, use of calendar, spread through trade, known for art, most important legacy was priestly leadership and devotion The Maya were the first Mesoamerican civilization, starting around 2600 B.C. They lasted the longest of all and are often viewed as the greatest Mesoamerican civilization. ... So the Olmecs were the first major Mesoamerican culture, despite being younger than the Mayans.

gupta empire

(320-550 CE) The decentralized empire that emerged after the Mauryan Empire, and whose founder is Chandra Gupta. The Gupta Empire was an ancient Indian empire existing from the mid-to-late 3rd century CE to 543 CE. At its zenith, from approximately 319 to 543 CE, it covered much of the Indian subcontinent. This period is considered as the Golden Age of India by some historians.

sumer civilization

(ca. 4500 - 2270 BCE) An ancient civilization in southern Mesopotamia, or modern-day Iraq. Sumerian cuneiform is the oldest example of writing in the world.

-esque

(forming adjectives) in the style of; resembling.

archaea vs bacteria

-Bacteria have peptidoglycan in their cell walls, Archaea don't -Bacteria can form spores, Archaea cannot -Archaea live in ancient-like environments (very hot, very acidic, very salty: hot springs, salt lakes, marshes), bacteria are ubiquitous The general cell structure of archaea and bacteria are the same but composition and organization of some structures differ in archaea. Similar to bacteria, archaea do not have interior membranes but both have a cell wall and use flagella to swim. Archaea differ in the fact that their cell wall does not contain peptidoglycan and cell membrane uses ether linked lipids as opposed to ester linked lipids in bacteria. Archaea reproduce asexually by the process of binary fission, budding and fragmentation. Eubacteria reproduce asexually through binary fission, budding, fragmentation, but eubacteria have the unique ability to form spores to remain dormant over years, a trait that is not exhibited by Archaea. Bacteria growth follows in three phases, the lag phase when cells adapt to new environment, log phase marking exponential growth and stationary phase when nutrients get depleted. Archaea can survive in extreme and harsh environments like hot springs, salt lakes, marshlands, oceans, gut of ruminants and humans. Eubacteria are ubiquitous and are found in soil, hot springs, radioactive waste water, Earth's crust, organic matter, bodies of plants and animals etc.

"He was excruciatingly focused," says Weinstein. "Not like mad-scientist focused, but he was capable of really focusing, in a crazy way, on certain things. He was extremely disciplined, which is how he is able to do all these things."

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"One day you'll understand that it's harder to be kind than clever."

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A civilization falling. Nuclear power forgotten. Science fading to mythology -- until the Foundation had stepped in.

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A hypothesis "graduating" to become a theory.

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All monosaccharides have two things: - A carbonyl group, or a carbon that forms a double bond with an oxygen (written as C=O), and also single bonds with two other atom friends that we call A and B (four bonds total for carbon) - Some hydroxyl groups (-OH) If the carbonyl group is at the end of the carbon backbone, and it makes a single covalent bond with H as well as one other atom friend, we call that sugar an aldehyde. The aldehyde group is written as RCHO. R = an unknown atom friend. If the carbonyl group is in the middle of the chain and bound to two other atom friends, then it's a ketone. The ketone group is written as RCOR'. R and R' = two unknown friends that may or may not be different from each other. The placement of other atoms and atom groups matter as well. In fact, some sugars differ only in the arrangement of hydrogen and hydroxyl groups along the carbon backbone. All of these differences may seem pretty minor and technical, but they have substantial effects on the behavior of the overall molecule. To put this in perspective, some of us take for granted that our heads are attached to the top-end of our spinal columns. If, however, our heads joined with one of the vertebrae in the middle of our backs instead, we'd really need to change the way we do things. Now you know where these sugars are coming from when they place importance on the arrangement of their atoms. Common monosaccharides include: Glucose, C6H12O6 Galactose, C6H12O6 Fructose, C6H12O6 You may have noticed that they all have the same molecular formula. How can this be, you ask? Arrangement of atoms! When two monosaccharide rings join (by dehydration synthesis, no less) to form a bigger sugar, they are called a disaccharide ("two sugars"). Sucrose, or table sugar, is a disaccharide that is formed from glucose and fructose. Lactose is a disaccharide composed of glucose and galactose. The most abundant carb on the planet is cellulose—the hard stuff plants are made of—but few organisms can actually break it down to eat it. For starters, all biological molecules use a relatively small number of building blocks—our favorite word, monomers—to make a diverse array of larger polymers. You might even call them biopolymers. Within each class of biomolecules, carbohydrates, lipids, proteins, and nucleic acids, there is unity in the fact that the same monomers are used again and again, and diversity results from putting the monomers together in different ways. Glucose is a 6-carbon ring. Therefore, if the fourth carbon of one glucose monomer binds with the first carbon of a second glucose monomer, and this happens lots and lots of times so that lots and lots of bonds form, we will have a chain with no branches. (In fact, this starch is called amylose.) However, if some glucose molecules deviate from this bonding pattern, we can get a branched form of starch. Different starches are united by the fact that they have the exact same building blocks, and diversity arises when those building blocks are assembled in different ways. Cellulose, like starch and glycogen, is made from glucose monomers, but they bond together in a different way. In the storage molecules starch and glycogen, all the glucose molecules are right-side-up, and animals have enzymes that can deal with these kinds of bonds. In cellulose, however, every other glucose monomer is upside down, creating a different sort of bond. Animal enzymes are perplexed by this and cannot figure out how to break these bonds. Some animals, like cows, have microbes in their digestive tracts that are able to break these bonds, and they are some of a very few that can get a little energy from cellulose. For everyone who isn't lucky enough to have a little clan of helpful, cellulose-digesting microbes, including us humans, cellulose passes through our systems undigested. This cellulose is famously known as fiber. Metamucil, anyone? Chitin is another structural polysaccharide, but this one is found in fungi (mushrooms and whatnot) and some animals. It's made of glucose like the other polysaccharides but has some nitrogen thrown in the mix for good measure. Chitin comprises the hard exoskeleton of arthropods, like insects and crustaceans, and strengthens the cell walls of fungi. Since fungi and animals share a more recent common ancestor than either one shares with plants, it makes some evolutionary sense that animals and fungi share this important structural polysaccharide. Yes, you read that correctly. A mushroom is more closely related to you than it is to any plant. Hey, everyone's extended family has a few nuts. Er, mushrooms. As it turns out, animals and fungi share a common ancestor and branched away from plants at some point about 1.1 billion years ago. It was only later that animals and fungi separated on the genealogical tree of life, making mushrooms more closely related to humans than plants

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All steroids are composed of carbon rings stuck together by dehydration synthesis—four rings, to be exact. They may have various other chains of atoms hanging off one or more rings, but at heart, they all share the four carbon rings. Cholesterol is one kind of steroid, which you may have heard good and bad (but mostly bad) things about. Many hormones, including testosterone, estradiol, and stress hormones, are steroids, too. Who knew? Your cell membranes are made of lipids, and some viruses hijack those lipids in order to hide from your immune system and invade other cells. One of these nasty viruses is HIV.

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Although your body does not contain helium, it does contain many of those ancient hydrogen atoms unchanged since the Universe began. Within a few hundred million years after the Big Bang, matter began to collect to form galaxies containing billions of stars. You have learned how nuclear reactions inside stars combine low-mass atoms, such as hydrogen, to make heavier atoms. Generations of stars cooked the original particles, fusing them into atoms such as carbon, nitrogen, and oxygen (see Chapters 11 and 12). Those are common atoms in your body. Even the calcium atoms in your bones were assembled inside stars. Most of the iron in your body was produced by nuclear fusion reactions during explosions called supernovae that occur at the ends of the lives of stars more massive than the Sun, or by decay of radioactive atoms in the clouds of matter ejected by some supernovae. You will encounter these titanic explosions and their results in Chapter 11. Other atoms heavier than iron, for example, iodine that is critical in the function of your thyroid gland, plus atoms of other elements that are uncommon enough to be expensive such as gold, silver, and platinum, also are mostly or entirely made during the violent deaths of rare massive stars. The ability of hemoglobin to function and allow you to breathe is the result of a supernovae... Our Galaxy contains at least 100 billion stars, including the Sun. It formed from a cloud of gas and dust about 5 billion years ago, and the atoms in your body were part of that cloud. How the Sun took shape, how the cloud gave birth to the planets, how the atoms in your body found their way onto Earth and into you is the story of this chapter. As you explore the origin of the Solar System, keep in mind the great chain of origins that created the atoms. As the geologist Preston Cloud remarked, "Stars have died that we might live."

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And that was when it hit me. Like an anvil falling out of the sky, directly onto my skull.

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Courage is knowing it might hurt and doing it anyway. Stupidity is the same. And that's why life is hard.

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In order for an celestial object to grow by gravitational collapse it must be 15 Earth masses. Gravitational collapse is the process by which a forming body such as a planet gravitationally captures gas rapidly from the surrounding nebula.

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In the OASIS, the classrooms were like holodecks. Teachers could take their students on a virtual field trip every day, without ever leaving the school grounds. Halliday and Morrow referred to the OASIS as an "open-source reality."

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Other cells are able to grow and reproduce without the services of other cells. Many bacteria fall into this category. The entire bacterial "organism" is just a single cell. The human "organism," in contrast, is estimated to have between 10 and 100 trillion cells. You read that right: trillions of cells. Take that, US federal deficit. What's more, some biologists estimate that there are 20 times more bacterial cells living inside the human body than there are actual human cells making up the body. We hope you aren't a germophobe, and if you are, this unit just might cure you.

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Proteins provide another great example of the intersection between structure and function. As we already know, proteins have four levels of structure: primary, or the sequence of amino acids; secondary, or the coils and folds from bonds between backbone elements; tertiary, or the coils and folds from bonds between R groups; and quaternary, or the conglomeration of more than one folded subunit. A protein is not a protein without its 3D structure, and regardless of what function it has, a protein is useless if its structure is somehow incorrect. Scientists in the field actually refer to proteins as having structure-function relationships. You don't get more thematic than that. What causes a protein to have the wrong shape? There are a couple conditions that can cause this misshaping to happen. If a mutation (read: unexpected alteration) in the genetic code causes the wrong amino acids to be incorporated into the protein's primary structure, later folding may be affected by that change. Sickle cell anemia is a blood disease caused by an incorrect amino acid in one of the subunits of hemoglobin. People with sickle cell anemia have a valine amino acid instead of a glutamic amino acid at a certain position along the polypeptide chain. This alteration causes improper folding of the hemoglobin subunit that leads to two problems: Reduced oxygen-carrying capacity Red blood cells that have the wrong shape Yes, you read correctly. In this case, proteins of the wrong shape lead to whole cells that are the wrong shape! Those misshapen cells clog blood vessels and prevent proper circulation.

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Somewhere along the way, I started to go overboard. I may, in fact, have started to go a little insane.

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They were constantly trying to prove they had acquired more obscure knowledge than everyone else.

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Time out: please meet phosphorus. He is an element with 15 protons, 15 electrons, and 16 neutrons. He loves to be a negatively charged ion and spends his days hanging out in a group called CHNOPS, or the six elements of life: Carbon Hydrogen Nitrogen Oxygen Phosphorus Sulfur Basically, they're the Rat Pack of the elemental world. The phosphate "head" of this big complex is polar, and you already know that fatty acids (or the "tails") are nonpolar. This creates quite the dual personality for the phospholipid. Does it hate water, or does it love it? Both! Cell membranes take advantage of these split tendencies by lining up two layers of phospholipids, with their nonpolar parts facing toward each other. The result is a barrier between the inside and outside of the cell. How convenient for a little blob of cellular machinery that needs some protection. This is called the phospholipid bilayer.

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To quote the Almanac: "People who live in glass houses should shut the f*ck up."

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Without the love of research, mere knowledge and intelligence cannot make a scientist.

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how many synthetic amino acids are there?

22 proteinogenic amino acids. over 80 amino acids created abiotically in high concentrations. about 900 are produced by natural pathways. over 118 engineered amino acids have been placed into protein. In biochemistry, non-coded or non-proteinogenic amino acids are those not naturally encoded or found in the genetic code of any organism. Despite the use of only 22 amino acids (21 in eukaryotes[note 1]) by the translational machinery to assemble proteins (the proteinogenic amino acids), over 140 amino acids are known to occur naturally in proteins and thousands more may occur in nature or be synthesized in the laboratory.[1] Many non-proteinogenic amino acids are noteworthy because they are; intermediates in biosynthesis, post-translationally formed in proteins, possess a physiological role (e.g. components of bacterial cell walls, neurotransmitters and toxins), natural or man-made pharmacological compounds, present in meteorites and in prebiotic experiments (e.g. Miller-Urey experiment).

Cerberus

3-headed dog guarding the entrance to Hades In Greek mythology, Cerberus, often referred to as the hound of Hades, is a multi-headed dog that guards the gates of the Underworld to prevent the dead from leaving.

diameter of earth

7,917.5 mi

Blazar

A blazar is an active galactic nucleus (AGN) with a relativistic jet (a jet composed of ionized matter traveling at nearly the speed of light) directed very nearly towards an observer. Relativistic beaming of electromagnetic radiation from the jet makes blazars appear much brighter than they would be if the jet were pointed in a direction away from Earth.[1] Blazars are powerful sources of emission across the electromagnetic spectrum and are observed to be sources of high-energy gamma ray photons. Blazars are highly variable sources, often undergoing rapid and dramatic fluctuations in brightness on short timescales (hours to days). Some blazar jets exhibit apparent superluminal motion, another consequence of material in the jet traveling toward the observer at nearly the speed of light.

Protoplanet

A body that grows by the accumulation of planetesimals but has not yet become big enough to be called a planet.

dehydration synthesis

A chemical reaction in which two molecules covalently bond to each other with the removal of a water molecule. In chemistry, a dehydration reaction is a conversion that involves the loss of water from the reacting molecule or ion. Dehydration reactions are common processes, the reverse of a hydration reaction. Common dehydrating agents used in organic synthesis include sulfuric acid and alumina. Process used to turn monomers into polymers. There is a process by which this joining usually occurs, and it's called dehydration synthesis. The process begins when two monomers line up next to each other. Just when you think they're going to start line dancing, a hydrogen (H) from one monomer binds with a hydroxyl group (OH) from the other monomer, and voilà! A water molecule is born: H+ + OH- = H2O. While this is happening, the two monomers are binding to each other where they were bound to their respective hydrogen (-H) or hydroxyl (-OH) groups. (We add a dash to molecular groups, to show that they are attached to something else.) Having bonded, our lonely monomers are now a single polymer. This blissful union is presided over by an enzyme, which is mainly there to help speed things along. The name of this whole process is dehydration synthesis because monomers are literally coming together and synthesizing a polymer by dehydrating, or removing a water molecule.

phospholipid bilayer

A double layer of phospholipids that makes up plasma and organelle membranes. Take the phospholipid bilayer. Recall that phospholipids are one kind of lipid; they have a glycerol backbone with two fatty acid "tails" and a phosphate "head." How does the structure of a phospholipid allow it to carry out its function? 1. The fact that the tails are hydrophobic means that they do not interact with water. When a bunch of phospholipids are floating around in water, they try to arrange themselves in a bilayer that shields the hydrophobic parts from water-based, or aqueous, surroundings. 2. The heads are hydrophilic and can then interact with water and other polar or charged substances on either side of the bilayer. The bilayer acts as a barrier that allows cells to maintain internal conditions that are different from external conditions, which is monumentally important for cells to operate properly. Everything from nerve impulse conduction to muscle firing to cellular metabolism depends on the cell's ability to maintain different conditions on opposite sides of the bilayer. 3. Phospholipids demonstrate the intersection of structure and function in another way, too. We already know that fatty acids can be saturated or unsaturated and that unsaturated fatty acids have bends in their chains. Those bends prevent fatty acids from packing closely together, which causes cell membranes (membrane = phospholipid bilayer + other stuff) that contain lots of unsaturated fatty acids to be more "fluid." Fluid describes fatty acids that cannot pack in as tightly, and as a result, they move more freely over the surface of the cell. It might be weird to think about cell membranes as fluids, but actually, this property is really important for proper membrane functioning. Enzymes need to move around in order to work, and if a membrane is not fluid enough, it might become impermeable (walled off) to certain substances that normally pass through the bilayer easily. In sum, the fact that phospholipids structurally have polar and nonpolar parts, and the fact that fatty acids can structurally be saturated or unsaturated, allow phospholipid bilayers to properly function in regulating a cell's contents.

Active galactic nucleus

A galaxy's core in which highly energetic objects or activities are located. An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much higher than normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not produced by stars. Such excess non-stellar emission has been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. A galaxy hosting an AGN is called an "active galaxy." The non-stellar radiation from an AGN is theorized to result from the accretion of matter by a supermassive black hole at the center of its host galaxy.

Why terrestrial planets don't have rings?

A large mass makes it easier for a planet to hold onto orbiting ring particles; and, being farther from the Sun, the ring particles are not as easily swept away by the pressure of sunlight and the solar wind. It is hardly surprising, then, that the Terrestrial planets, low-mass worlds located near the Sun, have no planetary rings.

Minute and second of arc

A minute of arc, arcminute (arcmin), arc minute, or minute arc is a unit of angular measurement equal to 1/60 of one degree. Since one degree is 1/360 of a turn (or complete rotation), one minute of arc is 1/21,600 of a turn. A second of arc, arcsecond (arcsec), or arc second is 1/60 of an arcminute, 1/3,600 of a degree, 1/1,296,000 of a turn.

cytoskeleton

A network of fibers that holds the cell together, helps the cell to keep its shape, and aids in movement The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including bacteria and archaea. It extends from the cell nucleus to the cell membrane and is composed of similar proteins in the various organisms.

nitrogenous base vs nucleotide vs nucleoside

A nitrogenous base is simply a nitrogen-containing molecule that has the same chemical properties as a base. They are particularly important since they make up the building blocks of DNA and RNA: adenine, guanine, cytosine, thymine and uracil. A nucleotide consists of three things: A nitrogenous base, which can be either adenine, guanine, cytosine, or thymine (in the case of RNA, thymine is replaced by uracil). A five-carbon sugar, called deoxyribose because it is lacking an oxygen group on one of its carbons. One or more phosphate groups. Nucleotides are organic molecules that serve as the basic structural (monomer) units for DNA and RNA, which, as we know, are the building blocks responsible for all life on Earth. Each nucleotide contains a nitrogenous base, a five-carbon sugar, and at least one phosphate group. Nucleosides are glycosylamines that can be thought of as nucleotides without a phosphate group. A nucleoside consists simply of a nucleobase and a five-carbon sugar ribose whereas a nucleotide is composed of a nucleobase, a five-carbon sugar, and one or more phosphate groups.

passageway

A passageway is a hall or a walkway that connects one area to another. You might pass from a small museum through a passageway to an outdoor sculpture garden, for example.

Pentometer

A penetrometer may be used in botany to find the toughness of a leaf by measuring the force needed to punch a hole of a certain size through the leaf. Penetrometers are also used to measure the firmness of apples and other hard fruit. The Fall cone test, also called the cone penetrometer test or the Vasiljev cone test, is an alternative method to the Casagrande method for measuring the Liquid Limit of a soil sample proposed in 1942 by the Russian researcher Piotr Vasiljev (Russian: Пё́тр Васи́льев) and first mentioned in the russian standard GOST 5184 from 1949. It is often preferred to the Casagrande method because it is more repeatable and less variable with different operators.[1] Other advantages of the fall cone test include the alternative to estimate the undrained shear strength of a soil based on the fall cone factor K[2].

Inca Civilization

A pre-Columbian civilization in the Andes Mountains. The Inca excelled at engineering, and developed new food crops like potatoes. The Inca Empire was a vast empire that flourished in the Andean region of South America from the early 15th century A.D. up until its conquest by the Spanish in the 1530s. Even after the conquest, Inca leaders continued to resist the Spaniards up until 1572, when its last city, Vilcabamba, was captured 1200-1500

Protease

A protease (also called a peptidase or proteinase) is an enzyme that catalyzes (increases the rate of) proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids. They do this by cleaving the peptide bonds within proteins by hydrolysis, a reaction where water breaks bonds. Proteases are involved in many biological functions, including digestion of ingested proteins, protein catabolism (breakdown of old proteins), and cell signalling. Without additional helping mechanisms, proteolysis would be very slow, taking hundreds of years. Proteases can be found in all forms of life and viruses. They have independently evolved multiple times, and different classes of protease can perform the same reaction by completely different catalytic mechanisms.

Chaperonin

A protein molecule that assists in the proper folding of other proteins. Chaperonins are proteins that provide favourable conditions for the correct folding of other proteins, thus preventing aggregation. They prevent the misfolding of proteins, which prevents diseases such as Mad Cow Disease.

Heat shock protein

A protein that helps protect other proteins during heat stress. Heat-shock proteins are found in plants, animals, and microorganisms. Heat shock proteins (HSP) are a family of proteins that are produced by cells in response to exposure to stressful conditions. They were first described in relation to heat shock,[1] but are now known to also be expressed during other stresses including exposure to cold,[2] UV light[3] and during wound healing or tissue remodeling.[4] Many members of this group perform chaperone functions by stabilizing new proteins to ensure correct folding or by helping to refold proteins that were damaged by the cell stress.[5] This increase in expression is transcriptionally regulated. The dramatic upregulation of the heat shock proteins is a key part of the heat shock response and is induced primarily by heat shock factor (HSF).[6] HSPs are found in virtually all living organisms, from bacteria to humans.

debris disk

A ring-shaped circumstellar disk of dust and debris in orbit around a star. Debris disks can be created as the next phase in planetary system development following the protoplanetary disk phase. They can also be formed by collisions between planetesimals or from asteroids and comets colliding with the star.

Edison circuit

A shared neutral is a connection in which a plurality of circuits use the same neutral connection. This is also known as a common neutral, and the circuits and neutral together are sometimes referred to as an Edison circuit.

Buffer

A solution that minimizes changes in pH when extraneous acids or bases are added to the solution. To understand buffers, we need to know a thing or two about acids and bases. Acids are substances that release hydrogen ions (H+) into a solution. HCl, or hydrochloric acid, is a compound formed by ionic bonds. When you drop it in water, the H+ and Cl- come apart because, as we said before, water is polar and will attack charged ions. Cue the paparazzi and/or vulture imagery. As a result, a whole bunch of H+ ions are released into the solution, which dramatically increases the concentration of H+. An increase in the concentration of H+ causes an increase in acidity. A base, on the other hand, is a substance that will bind to the free hydrogen ions (H+) that might be floating around in a solution. Bases are also known as alkaline. NaOH is an example of a base. When you drop NaOH in water, the Na+ ions become separated from the hydroxide ions (OH-). Even though the oxygen and hydrogen of OH- are bound together covalently, they still count as an ion because the unit possesses an extra electron; therefore, it has a net negative charge. You can probably guess what happens when a stray OH- ion encounters a free H+ ion: it's love at first sight, and the ions bind. What happens as a result? The concentration of free H+ ions in that solution decreases, which increases the basicity. Bases have more OH- ions than acids. In summary, acids release a bunch of H+ ions into a solution, and bases mop them up like they're Swiffer. Two things to remember: - If there are relatively more H+ ions, the pH goes down, increasing the acidity. More H+, more acidic, lower pH. - If there are fewer H+ ions, the pH increases, increasing the basicity. Less H+, more basic, higher pH. Remember that the pH scale runs from 0 to 14, and each step represents a tenfold difference. In other words, a solution with a pH of 5 is 100 times more acidic than something with a pH of 7. And a solution with a pH of 3 is 10,000 times more acidic than something with a pH of 7. To put this in perspective, soda has a pH of 3. Kind of makes you want to rethink that Big Gulp, doesn't it? Okay, back to buffers. A buffer is a substance that helps to moderate any changes in pH that result from the addition of acids or bases. This is important because, as you'll learn later, most of the chemical processes that occur in living organisms are highly sensitive to pH, and drastic changes in pH can cause some serious trouble. Buffers are basically well-meaning control freaks. Water, as stated at the beginning of this section, can act like a buffer if there is a sudden change in pH. At any given moment, there are a few H2O molecules that break apart and form H+ and OH-. Don't worry. Most of the water molecules are still completely bound together, but there are a few hydrogen ions here and there who effectively get tired of "sharing" an electron with the pushy, selfish oxygen atoms. They throw their little atomic arms up and shout, "Fine! The electron is all yours. I'm outta here!" Therefore, there are always a few stray H+ and corresponding OH- ions floating around in a solution. These few dissociated water molecules are what give water its buffering ability. If we add an acid to water, some of the free OH- ions will bind to the newly added H+ ions, which will moderate the decrease in pH. Similarly, if we add a whole bunch of base to water, some of the added base will bind to the free H+ ions in solution, which will moderate the increase in pH. Having said all of this, while water can be a buffer, it isn't a fantastic one since most of the H2O molecules remain completely stuck together. It has a little bit of buffering capability and is helpful with small changes in pH, but it is by no means the best and certainly can't compensate for super drastic changes in pH. Second, water has a high heat of vaporization, the amount of heat required to convert liquid water into gaseous water (aka steam). Water's high heat of vaporization is thanks to those pesky hydrogen bonds. Water molecules at the surface need to be moving really fast to break free into the air. Heating increases the movement of the molecules, but we already know it takes a lot of energy to heat water because water has a high specific heat. If we put these two concepts together, we find that it takes a lot of energy to heat a water molecule, and we need to heat it a lot to give it the kinetic energy it needs to break the hydrogen bonds holding it to the rest of the water molecules. A double whammy if you're trying to get water to boil.

Age of the Earth and Solar System

Age of earth determined by radio-dating zircon crystals from Australia. Lower limit of 4.4 billion years Age of solar system from dating carbonaceous chondrite meteorites. Lower limit of 4.56 billion years. Age of moon from Apollo mission rocks. Lower limit 4.48 billion years. Age of Mars from meteorites that landed on earth. Lower limit 4.5 billion years Following the development of radiometric age-dating in the early 20th century, measurements of lead in uranium-rich minerals showed that some were in excess of a billion years old. The oldest such minerals analyzed to date—small crystals of zircon from the Jack Hills of Western Australia—are at least 4.404 billion years old. Calcium-aluminium-rich inclusions—the oldest known solid constituents within meteorites that are formed within the Solar System—are 4.567 billion years old,[10][11] giving a lower limit for the age of the Solar System.

Mitochondria

All cells need energy to grow, reproduce, and function. Like the organisms they comprise, cells must "eat" to obtain the energy they need. One of the most important types of cellular food is a molecule called glucose, which is a type of sugar and a carbohydrate. Eukaryotic cells take in glucose through proteins that cross the plasma membrane and then transport it through the cytoskeleton to the mitochondria (mitochondria is plural; the singular is mitochondrion) in the cytoplasm. The mitochondrion is often called the cell's powerhouse. In the cytoplasm just outside the mitochondria, glucose is broken down into smaller molecules through a process called glycolysis (literally "sugar breaking"), which releases chemical energy. This energy is temporarily captured by specialized molecules and transported through the mitochondrial membranes into the mitochondria. There it is used to make an important molecule called adenosine triphosphate (ATP) through a process known as cellular respiration. Mitochondria can convert a single molecule of glucose into ~38 molecules of ATP! You can think of each ATP molecule as a unit of stored energy ready to be used by the cell whenever needed. Mitochondria do not mess around with energy storage. So the main function of all mitochondria is to make ATP, which is the energy source for nearly all cellular functions and processes. The mitochondrion used to be a free living bacterial cell a wicked long time ago. Because of this fact, it has its own genome; however, because it relies so much on its host cell, it has lost many of its genes. The typical human cell has several hundred mitochondria, cytoplasmic organelles that convert energy to forms that can be used to drive cellular reactions. Without them cells would be dependent on anaerobic glycolysis for all their adenosine triphosphate (ATP). The mitochondria have a characteristic double membrane structure, in which the outer membrane contains large channel-forming proteins (called porin) and is permeable to all molecules of 5000 daltons or less, while the inner membrane is impermeable to most small ions and is intricately folded, forming structures called cristae. The large surface area of the inner mitochondrial membrane accommodates respiratory chain and ATP synthase enzymes involved in the process of oxidative phosphorylation (OXPHOS). The mitochondrial matrix contains hundreds of enzymes, including those required for the oxidation of pyruvate and fatty acids and those active in the tricarboxylic acid (TCA) cycle. The matrix also contains several identical copies of the mitochondrial DNA, mitochondrial ribosomes, tRNAs and various enzymes required for the transcription and translation of mitochondrial genes (see Alberts et al. 1994). Only a small fraction of the total free energy potentially available from glucose is released in glycolysis. The metabolism of carbohydrates is completed in the mitochondria when pyruvate is imported and oxidized by molecular oxygen (O2) to CO2 and water. The energy released is harnessed so efficiently that about 30 molecules of ATP are produced for each molecule of glucose oxidized, whereas only 2 molecules of ATP are produced by glycolysis alone. Oxidative metabolism in mitochondria is fuelled not only by pyruvate produced from carbohydrates by glycolysis in the cytosol but also by fatty acids. Pyruvate and fatty acids (from triglycerides) are selectively transported from the cytosol into the mitochondrial matrix, where they are broken down into the two-carbon acetyl group on acetyl coenzyme A (acetyl CoA) by the pyruvate dehydrogenase complex and the β-oxidation pathway, respectively. The acetyl group is then fed into the tricarboxylic acid cycle for further degradation, and the process ends with the passage of acetyl-derived high-energy electrons along the respiratory chain. http://jultika.oulu.fi/files/isbn9514255674.pdf

Prokaryotic Genetic Material

All prokaryotic cells contain large quantities of genetic material in the form of DNA and RNA. Because prokaryotic cells, by definition, do not have a nucleus, a single large circular strand of DNA containing most of the genes needed for cell growth, survival, and reproduction is found in the cytoplasm. This chromosomal DNA tends to look like a mess of string in the middle of the cell: Usually, the DNA is spread throughout the entire cell, where it is readily accessible to be transcribed into messenger RNA (mRNA) that is immediately translated by ribosomes into protein. Sometimes, when biologists prepare prokaryotic cells for viewing under a microscope, the DNA will condense in one part of the cell to produce a darkened area called a nucleoid. As in eukaryotic cells, the prokaryotic chromosome is intimately associated with special proteins involved in maintaining the chromosomal structure and regulating gene expression. In addition to a single large piece of chromosomal DNA, many prokaryotic cells also contain small pieces of DNA called plasmids. These circular rings of DNA are replicated independently of the chromosome and can be transferred from one prokaryotic cell to another through pili, which are small projections of the cell membrane that can form physical channels with the pili of adjacent cells. The transfer of plasmids between one cell and another is often referred to as "bacterial sex." Sounds dirty. The genes for antibiotic resistance, or the gradual ineffectiveness of antibiotics in populations, are often carried on plasmids. If these plasmids get transferred from resistant cells to nonresistant cells, bacterial infection in populations can become much harder to control. For example, it was recently learned that the superbug MRSA, or multidrug-resistant Staphylococcus aureus, received some of its drug-resistance genes on plasmids. Prokaryotic cells are often viewed as "simpler" or "less complex" than eukaryotic cells. In some ways, this is true. Prokaryotic cells usually have fewer visible structures, and the structures they do have are smaller than those seen in eukaryotic cells. Do not be fooled. Just because prokaryotic cells seem "simple" does not mean that they are somehow inferior to or lower than eukaryotic cells and organisms. Making this assumption can get you into some serious trouble. Biologists are now learning that bacteria are able to communicate and collaborate with one another on a level of complexity that rivals any communication system ever developed by humans5. Take that, Facebook and Twitter! Prokaryotes sure showed you. In addition, some archaean cells are able to thrive in environments so hostile that no eukaryotic cell would survive for more than a few seconds6. You try living in a hot spring, salt lake, volcano, or even deep underground.Prokaryotic cells are also able to pull off stuff that eukaryotic cells could only dream of, in part because of their increased simplicity. Being bigger and more complex is not always better. One kind of bacterial communication, also known as quorum sensing, is where small chemical signals are used to count how many bacteria there are.

How do you know that all prokaryotic cells make proteins?

All prokaryotic cells have ribosomes, the cellular structure responsible for making proteins.

What are the 4 steps of an action potential?

An action potential is caused by either threshold or suprathreshold stimuli upon a neuron. It consists of four phases; hypopolarization, depolarization, overshoot, and repolarization. An action potential propagates along the cell membrane of an axon until it reaches the terminal button.

Reverse transcriptase

An enzyme encoded by some certain viruses (retroviruses) that uses RNA as a template for DNA synthesis. A reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template, a process termed reverse transcription. Reverse transcriptases are used by retroviruses to replicate their genomes, by retrotransposon mobile genetic elements to proliferate within the host genome, by eukaryotic cells to extend the telomeres at the ends of their linear chromosomes, and by some non-retroviruses such as the hepatitis B virus, a member of the Hepadnaviridae, which are dsDNA-RT viruses.

How does "even if this flu shot isn't an exact match, if you do get the flu it won't be as bad" work?

An imperfect match will still elicit imperfect antibodies. Imperfect antibodies simply bind and neutralize the virus less effectively than perfect ones, but they still do it. Thus the intensity and duration of your flu will be less, since your body will still have a head start on fighting it off compared to having no anti-flu antibodies. A perfect match is no guarantee of total protection either by the way. It still gives your body the best head start possible, but if you happen to get a particularly huge dose of virus at initial infection, the virus could still outrun your immune response. This is why it is important to get your flu shot every single year, even if it isn't perfectly effective every year. Each year you get a flu shot acts like a booster for every year in the future in which you may be exposed to flu.

indenturement

An indenture is a legal contract that reflects or covers a debt or purchase obligation. It specifically refers to two types of practices: in historical usage, an indentured servant status, and in modern usage, it is an instrument used for commercial debt or real estate transaction. An indenture is a formal legal agreement. Many earned passage to the British colonies by indenturing, or selling, themselves to a master for a period of seven years--they were called indentured laborers.

Why do hydrophobic portions of proteins fold towards the inside?

As a protein's polypeptide chain is synthesized (read: made), it immediately begins folding into a compact structure. During folding in water-based solutions, proteins tend to bury their hydrophobic, or water-fearing, amino acids on the inside of the structure, and interactions form between different portions of the polypeptide chain. Why might a protein want to hide its hydrophobic amino acids? Because the cell is mostly water. When a protein has lost its highly folded, low-energy conformation, we call it a denatured protein. Certain solvents, or liquids that like to dissolve other molecules, like those with wacky pHs or high salt concentrations, and high temperature will successfully denature a protein. These conditions interfere with the protein's intramolecular interactions, or interactions between different parts of the same protein molecule, which causes it to unfold. Sometimes, a protein can refold on its own once the denaturing conditions are removed, a process called...renaturing. Most of the time, though, proteins need the help of other proteins, called chaperones, to fold, or refold, after denaturation. (Side note: You may remember the word "chaperonins" from another unit. Chaperonins are a specific type of chaperone. You're welcome.) Chaperones work by binding to the partially folded protein and encouraging it to take on the structure that is the most energetically favorable. It's helpful to think of protein folding in terms of an energy diagram. A correctly folded protein will remain in the shape that allowed it to reach its lowest point of energy on the energy curve. The million-dollar question at this point is: What happens if a protein doesn't fold correctly? The answer is that normally, the cell degrades, or destroys, improperly folded proteins. Sometimes, though, improperly folded proteins can escape the cell's quality control. This tends to have less than optimal consequences. For instance, a protein that has incorrectly left its hydrophobic amino acids exposed is not just indecent and a waste of space.; it can actually be hazardous to the cell! Exposed hydrophobic protein regions can cause proteins to aggregate (clump together), become undissolved, and fall out of solution. Neurons, or your brain cells, are particularly sensitive to protein aggregation. The sad reality is that many neurodegenerative diseases such as mad cow disease and Alzheimer's disease are caused by the aggregation of improperly folded proteins. Despite their common roles in catalyzing biochemical reactions, the diversity of enzymes is massive and daunting. In fact, not all enzymes are even proteins! Some of the "oldest" enzymes around are thought to be RNA enzymes, called ribozymes. (RNA is a nucleic acid called ribonucleic acid. Refresh your memory in the Biomolecules unit.) While RNA is often thought of as a messenger and an intermediate between DNA and proteins, scientists now believe that early in the history of Life, RNA played a much more central role. Scientists discuss the possibility of an "RNA world" where neither DNA nor proteins existed. In this scenario, RNA molecules acted both as storage of genetic material and as enzymes catalyzing important biological reactions. According to this hypothesis, fittingly called the RNA world hypothesis (scientists are so creative), only later on in evolution did DNA and proteins predominantly take over these roles. Even in organisms today, ribozymes play critical roles in the cell. While the ribosome consists of many proteins, it is the ribosomal RNA in the large subunit that catalyzes the joining of amino acids in the synthesis of proteins. You'll learn a lot more about ribosomal "RNAs" later, but right now, you can appreciate the fact that RNA can take on complicated structures just like proteins can, and can catalyze important biological reactions to boot. Not all humans have the same bacteria, either. For example, a special microbe called Bacteroides plebeius is found predominantly in the digestive tract of people of Japan, and it contains enzymes that help them digest seaweed. The diversity of microbes, and the enzymes that they contain, have allowed termites to use that super tasty wood as a food source.

What causes asteroids to form?

Asteroids are leftovers from the formation of our solar system about 4.6 billion years ago. Early on, the birth of Jupiter prevented any planetary bodies from forming in the gap between Mars and Jupiter, causing the small objects that were there to collide with each other and fragment into the asteroids seen today. Protoplanet remnants and leftover collision debris

are tardigrades eukaryotes?

At one time water bears were candidates to be the main model organism for studies of development. That role is now held most prominently by the roundworm Caenorhabditis elegans, the object of study for the many distinguished researchers following in the trail opened by Nobel Prize laureate Sydney Brenner, who began working on C. elegans in 1974. Water bears offer the same virtues that have made C. elegans so valuable for developmental studies: physiological simplicity, a fast breeding cycle and a precise, highly patterned development plan. Some species may, like C. elegans, be eutelic, meaning that the organisms retain the same number of cells through their development. Tardigrades have somewhere over 1,000 cells. I and others use water bears as a model educational organism to teach a wide range of principles in life science. Taxonomists divide life on Earth into three domains: Bacteria, Archaea (an ancient line of bacterialike cells without nuclei that are likely closer in evolutionary terms to organisms with nucleated cells than to bacteria), and Eukarya. Eukarya is divided into four kingdoms: Protista, Plantae, Fungi and Animalia. Phylum Tardigrada is one of the 36 phyla (roughly, depending on whom one asks) within Animalia—making water bears a significantly distinctive branch on the tree of life. Animals grow in either of two ways, by adding more cells or by making each cell larger. Tardigrades generally do the latter. If an animal has a hard cuticle or exoskeleton, it must break out of that shell in order to grow. For example, in summer in many parts of the world, one encounters the shed exoskeletons of locusts on trees everywhere. Tardigrades are divided into two classes, Eutardigrada and Heterotardigrada. As a general rule, the members of Eutardigrada have a naked or smooth cuticle without plates, whereas the Heterotardigrada boast a cuticle armored with plates. Terrestrial tardigrades have three basic states of being: active, anoxybiosis and cryptobiosis. In the active state, they eat, grow, fight, reproduce, move and enact the normal routines of life. Anoxybiosis occurs in response to low oxygen. Tardigrades are quite sensitive to oxygen tension. Prolonged asphyxia results in failure of the osmoregulatory controls that regulate body water, causing the tardigrade to puff up like the Michelin Man and float around for a few days until its habitat dries out and it can resume active life. Cryptobiosis is a reversible ametabolic state—the suspension of metabolism—that has inevitably been compared to death and resurrection. In cryptobiosis, brought on by extreme desiccation, metabolic activity is paralyzed due to the absence of liquid water. Terrestrial water bears are only limnoterrestrial—aquatic animals living within a film of water found in their terrestrial habitats. Moss and lichens provide spongelike habitats featuring a myriad of small pockets of water and, like sponges, these habitats dry out slowly. As its surroundings lose water, the tardigrade desiccates with them. It has no choice. The creature loses up to 97 percent of its body moisture and shrivels into a structure about one-third its original size, called a tun. In this state, a form of cryptobiosis called anhydrobiosis—meaning life without water—the animal can survive just about anything. Tardigrades have been experimentally subjected to temperatures of 0.05 kelvins (-272.95 degrees Celsius or functional absolute zero) for 20 hours, then warmed, rehydrated and returned to active life. They have been stored at -200 degrees Celsius for 20 months and have survived. They have been exposed to 150 Celsius, far above the boiling point of water, and have been revived. They have been subjected to more than 40,000 kilopascals of pressure and excess concentrations of suffocating gasses (carbon monoxide, carbon dioxide, nitrogen, sulfur dioxide), and still they returned to active life. In the cryptobiotic state, the animals even survived the burning ultraviolet radiation of space. Anhydrobiosis—metabolic suspension brought on by nearly complete desiccation—is a common state for tardigrades, which they may enter several times a year. To survive the transition, water bears must dry out very slowly. The tun forms as the animal retracts its legs and head and curls into a ball, which minimizes surface area. When nearly all of its internal water has been surrendered, the tardigrade is in anabiosis, a dry state of suspended animation. It is almost as if the animal preserves itself by becoming a powder comprised of the ingredients of life. When rehydrated by dew, rain or melting snow, tardigrades can return to their active state in a few minutes to a few hours. In cryobiosis, another form of cryptobiosis, the animal undergoes freezing yet can be revived. Any temperature below the cell cytoplasm's freezing point suppresses molecular mobility and therefore suspends metabolism. Deep-freeze temperatures could be expected to cause additional structural disruptions, yet tardigrades, as noted above, have survived the most drastic chills. It seems likely that survival is conferred by the release or synthesis of cryoprotectants. These agents may manipulate tissue freezing temperature, slowing the process and allowing an orderly transition into cryobiosis, and they may suppress the nucleation of ice crystals, resulting in an ice-crystal form that is favorable for subsequent revival with thawing. Osmobiosis is a response to extreme salinity, which can cause destructive osmotic swelling. Some tardigrades exhibit strikingly effective osmoregulation, maintaining stasis in the face of steep osmotic gradients. Some others escape via formation of a tun that is impervious to osmotic transfer. In 2007, tardigrades became the first multicellular animal to survive exposure to the lethal environs of outer space. Researchers in Europe launched an experiment on the European Space Agency's BIOPAN 6/Foton-M3 mission that exposed cryptobiotic tardigrades directly to solar radiation, heat and the vacuum of space. While the experimental vessel orbited 260 kilometers above the Earth, the researchers triggered the opening of a container with tardigrade tuns inside and exposed them to the Sun. When the tuns were returned to Earth and rehydrated, the animals moved, ate, grew, shed and reproduced. They had survived. In summer of 2011, Project Biokis, sponsored by the Italian Space Agency, ferried tardigrades into space on the U.S. space shuttle Endeavor. Colonies of tardigrades were exposed to different levels of ionizing radiation. The damage is now being assayed to learn more about how cells react to radiation and, perhaps, how tardigrade cells fend off its damage. How far is the nearest solar system? Could cryptobiotic tardigrades make it to Earth? Surviving intense radiation suggests an especially effective DNA repair system in an active organism. Effective osmoregulation in extreme salinity implies a vigorous metabolism—osmoregulation in the face of high environmental salinity is energetically extremely expensive as metabolic transactions go, requiring the pumping of ions against steep osmotic and ionic gradients. Thus, we see in tardigrades two opposing responses to environmental extremes: the passive response of dormancy in the form of cryptobiosis, balanced by the hyperactive responses of impressive DNA repair and high-performance osmoregulation. As practitioners of adaptive evolution, tardigrades are virtuosos. Tardigrades have been discovered just about everywhere that anyone has looked, from the Arctic to the equator, from intertidal zones to the deep ocean, and even at the top of forest canopies. Their ubiquity is intimately linked to their survivorship. I am often asked how tardigrades manage to find their way to the canopy of towering trees. Most likely, wind carries them. In the tun state they are barely distinguishable from dust particles. But like spores, pollen and seeds, the tuns have a preference for where they land. Many microenvironments will be unsuitable habitats for freshly arrived tardigrades. Yet an unhappily placed tun can simply wait for a change in precipitation or perhaps a change in season. When conditions improve, life can begin again. At present there are about 1,100 described species of water bears, but not all are valid. Some descriptions are repeats and some are just plain flawed. Around 1,000 species have been properly identified and described. We have about 300 marine, 100 freshwater and 600 terrestrial species. But the land species are much easier to find and have been pursued by many more researchers over many more years. Still, my students have discovered and described four new species so far, and we are working to confirm another half dozen, including one found on the campus of Baker University in Kansas, where I am a faculty member. We believe there is an abundance of species yet to be discovered, especially in the nonterrestrial environments. I might discover a new species? she asks. Yes, sitting at a microscope, you might observe an animal nobody in the world has ever seen before. That is pure exploration. In the blink of an eye, you might find a clue to the evolution of the phylum or identify the animal that holds the cure for cancer, I say. Then again, you might not. It took me 16 years to find my first new species. Most tardigrades are phytophagous (plant eaters) or bacteriophagous (bacteria eaters), but some are carnivorous to the extent that they eat smaller species of tardigrades (e.g., Milnesium tardigradum). Tardigrades share morphological characteristics with many species that differ largely by class.

Xerox's first successful copier burst into flame so often it came with a fire-extinguisher

Behold, 1959's groundbreaking Xerox 914, the first successful plain-paper photocopier, weighing in at 648 lbs, making a whopping 136 copies/hour. Much beloved for its propensity to burst into flame while operating, an occasion considered so normal by the manufacturer that they shipped it with a mini fire-extinguisher, euphemistically called a "scorch guard."

Endoplasmic Reticulum (ER)

Both ER types are involved in making important cellular components. The rough endoplasmic reticulum (RER) is mainly responsible for the synthesis and processing of proteins that are either secreted from the cell or that end up stuck in the plasma membrane. Proteins marked for secretion are sent from the RER to the Golgi body (it's next up for explanation, so hang tight) for further processing. Insulin is an example of a secreted protein processed by the RER. This very large protein is secreted in huge quantities from the pancreas cells in mammals and aids in the uptake and digestion of glucose. The smooth endoplasmic reticulum (SER) is primarily involved in the synthesis of lipids (aka fatty fat fats) and steroids, both very important components of cell membranes. The lipids made in the SER are combined with phosphorous to make phospholipids, the most abundant component of cell membranes. Steroids, including cholesterol, made in the SER are also important components of cell membranes, because they provide the rigidity and structure needed for the membrane to keep its general shape.

Bromelain

Bromelain is an enzyme extract derived from the stems of pineapples, although it exists in all parts of the fresh pineapple.[1] The extract has a history of folk medicine use. As an ingredient, it is used in cosmetics, as a topical medication, and as a meat tenderizer. The term "bromelain" may refer to either of two protease enzymes extracted from the plants of the family Bromeliaceae, or it may refer to a combination of those enzymes along with other compounds produced in an extract.[1] Bromelain enzymes are called fruit bromelain and stem bromelain.

Centrioles

Cell organelle that aids in cell division in animal cells only The centriole's main function is to aid in cell division and in the spatial arrangement of structures within the cell. Less is known about the function of centrioles than many of the other organelles discussed in this section, but biologists are learning that these little protein tubes play a critical role in cellular reproduction and even cell growth. What's more, centrioles are now known to be essential for the development of flagella and cilia. Cells with damaged or missing centrioles cannot form properly functioning flagella and cilia, a condition that can lead to disease and even death of the organism.

CTE

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease caused by repeated head injuries. Symptoms may include behavioral problems, mood problems, and problems with thinking. Symptoms typically do not begin until years after the injuries. CTE often gets worse over time and can result in dementia.

What type of plant is a clover?

Clover or trefoil are common names for plants of the genus Trifolium (Latin, tres "three" + folium "leaf"), consisting of about 300 species of flowering plants in the legume or pea family Fabaceae.

how many stars are within 100 light years?

Depends on what type of star you are looking for. There are thousands within 100 light years. As many as 512 or more stars of spectral type "G" (not including white dwarf stellar remnants) are currently believed to be located within 100 light-years or (or 30.7 parsecs) of Sol -- including Sol itself. Only around 64 are located within 50 light-years (ly), while some 448 are estimated to lie between 50 and 100 light-years -- a volume of space that is seven times as large as the inner sphere within 50 ly of Sol. A comparison of the density of G-type stars between the two volumes of space indicates that the outer spherical shell has around 100 percent of the spatial density of known G-type stars as the inner spherical volume, which suggests that astronomers have identified the great majority of the G-type stars that are actually located within 100 ly of Sol, assuming the same spatial distribution in the Solar neighborhood. At least 76 stars of spectral type "A" (not including white dwarf stellar remnants) are currently believed to be located within 100 light-years or (or 30.7 parsecs) of Sol. Of those stars, astronomers believe that five have evolved out of the main sequence into giant stars, while an additional 17 or so may be subgiants (more on nearby giants and subgiants). Four A-type stars are the most luminous stars located within Sol's immediate neighborhood (within 10 parsecs or 32.6 light-years): Sirius A, Altair, Fomalhaut, and Vega. Due in part to their relatively proximity and abundance, these relatively brighter, large, and more massive stars are visually prominent objects in Earth's night sky, where five of the 20 brightest (in apparent magnitude) stars are spectral type A. By 1998, more than two thousand (2,026+) of spectral type "M" had been tentatively identified and estimated to be within 100 light-years (ly) or (or 30.7 parsecs) of Sol. Most M stars were too dim for the HIPPARCOS satellite mission to obtain an accurate parallax. Indeed, many, if not most, M stars located beyond 10 parsecs probably do not have a distance estimate within several of light-years. Lastly, many red dwarf stars identified as nearby objects between 10 and 31 parsecs since 1998 have not yet been added to the list slowly being edited below. The answer depends on how you limit the question. For instance, there are over 50 stars currently known to be within about 15 or 16 light years of the Sun, but only 8 (including the Sun) are visible to the naked eye in a dark sky, and just half that number are bright enough to see near a large city. At 100 light years, stars would be nearly 40 times fainter than at 15 to 16 light years, but the volume of space involved is almost 250 times greater, so the total number of stars should be about 250 times larger, but the numbers for stars of a given brightness would only increase by about a factor of 6; so perhaps a couple of dozen 'bright' stars, and 40 or 50 'dark-sky' stars would be on the list, out of well over ten thousand stars mostly too faint to see, even with fairly large telescopes.

Didanosine (ddI)

Didanosine (ddI, DDI), marketed under the trade names Videx, is a medication used to treat HIV/AIDS.[1] It is used in combination with other medications as part of highly active antiretroviral therapy (HAART). It is of the reverse-transcriptase inhibitor class. Didanosine (ddI) is a nucleoside analogue of adenosine.[9] It differs from other nucleoside analogues, because it does not have any of the regular bases, instead it has hypoxanthine attached to the sugar ring. Within the cell, ddI is phosphorylated to the active metabolite of dideoxyadenosine triphosphate, ddATP, by cellular enzymes. Like other anti-HIV nucleoside analogs, it acts as a chain terminator by incorporation and inhibits viral reverse transcriptase by competing with natural dATP.

Hurrians

Established the kingdom of Mitanni in the upper Tigris-Euphrates valley around 1500 B.C.E. which lasted for 100 years, until they were conquered by the Hittites.

What's the difference between cytoplasm and cytosol?

Everything inside the cell membrane except the nucleus is considered part of the cytoplasm. The cytosol is the gel-like fluid (or solution) in which all of the organelles and cytoskeleton are suspended or dissolved. Note: the common root in cytosol, solution, and dissolve is sol-. The cytosol is part of the cytoplasm.

Flagella and Cilia

Flagella and cilia are extensions of the cell membrane that are lined with cytoskeleton and, in the case of flagella, mitochondria. Flagella look like whips and are generally much longer than cilia, but there are often hundreds more cilia than flagella on a given cell. Flagella are primarily responsible for cell movement, and that whip-like appearance is no accident. By whipping about, a flagellum propels its cell through the environment. Sperm cells are an excellent example of animal cells sporting flagella. In these cells, flagella spin rapidly to push the sperm up the vaginal canal, into the uterus, and finally into the egg. Cilia, on the other hand, act more like short hairs moving back and forth across the outside of the cell. Cilia generally move matter past a cell. The most common examples of ciliated cells are those that line the trachea, or wind pipe, of animals. There, the cilia move mucus containing dirt and other inhaled particles up the windpipe and into the esophagus, where the particles can be coughed up or swallowed. The flagella and cilia in animal cells are not evolutionarily related to those found in bacterial cells; however, there are some strange little worms that cover their bodies with bacteria that look like flagella. Image is of Cilia under electron microscope

Researchers take small step toward silicon-based life

For life on Earth, carbon is king. All organisms build their cells from carbon-based molecules. Scientists and science fiction authors have long speculated that because silicon atoms bond to other atoms in a manner similar to carbon, silicon could form the basis of an alternative biochemistry of life. Yet even though silicon is widely available on Earth and makes up 28% of the planet's crust (versus 0.03% for carbon), the element is almost entirely absent from life's chemistry. That may soon change. Researchers reported in San Diego, California, this week at the semiannual meeting of the American Chemical Society that they have evolved a bacterial enzyme that efficiently incorporates silicon into simple hydrocarbons—a first for life. Down the road, organisms able to incorporate silicon into their cells could lead to a novel biochemistry for life, although for now creating actual silicon-based creatures (like the Horta from Star Trek, pictured) remains a long way off. To get biology to adopt silicon, Frances Arnold, a chemist at the California Institute of Technology (Caltech) in Pasadena, along with postdoctoral assistant Jennifer Kan and graduate student Rusty Lewis, started by isolating a so-called thermophilic bacterium, which grows in hot springs. Like many organisms, the bacterium contains an enzyme called cytochrome c, which shuttles electrons to other proteins, making it widely useful in biochemistry. In some cases, however, enzymes in thermophilic bacteria expand their roles to carry out other reactions on the side. So the Caltech researchers tested their microbe and found that in rare cases its cytochrome c also added silicon to hydrocarbons. In nature, Arnold notes, cytochrome c's silicon-adding ability is so feeble that it's probably just a byproduct of the enzyme's function—not even close to its primary role. To try to beef it up, the team incubated the bacteria with silicon and carbon compounds and selected the organisms that produced the most hydrocarbons that incorporated silicon. After only three rounds of this artificial selection, the enzymes had evolved to churn out silicon-containing hydrocarbons 2000 times as readily as natural cytochrome c. "The power of evolution really shows up when a new function appears and then is forced to adapt via directed evolution," Arnold says. For now, the silicon-spiked hydrocarbon compounds, called organosilanes, probably aren't useful either to the bacteria or to industry. They're short and stubby, unlike the long chainlike versions that chemical companies make for uses such as adhesives, caulks, and sealants.

Do plants get their energy from the soil?

Heck no. Plants, like animals, must have food in order to survive. But unlike most animals, plants make their own food energy through the process of photosynthesis. Plants use this food, in the form of glucose, in the same way that animals use the glucose they eat: it is converted into ATP by the mitochondria. Plants do, in fact, eat. Their source of food energy? Carbon dioxide (CO2) in the air. When you really think about it, plants are incredible because they can turn thin air into wood (and fruits, and flowers, and roots) without even thinking about it! Basically, every time you put food in your mouth, you are just eating super-processed air. We just made you feel a little less special, didn't we?

Elon Musk

How do you learn so much so fast? Lots of people read books and talk to other smart people, but you've taken it to a whole new level. I do kinda feel like my head is full! My context switching penalty is high and my process isolation is not what it used to be. Frankly, though, I think most people can learn a lot more than they think they can. They sell themselves short without trying. One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, i.e. the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to.

The paper passes through rollers in the fuser assembly, where temperatures up to 427 °C (801 °F) and pressure are used to permanently bond the toner to the paper. (For a laser printer) __________ Inkjet printers squirt tiny droplets of ink through equally tiny nozzles and onto paper. You can sort of imagine the nozzles as tiny water hoses, all turning on and off thousands of times per second. Sophisticated printer software controls all of the nozzles, shooting ink in precise patterns that make up your newest haiku or perhaps a picture of your cat lounging on your keyboard. There are two primary categories of inkjet ink: dye-based or pigment-based. Dye-based inks consist of colorants that are dissolved in a liquid. Pigmented inks, on the other hand, use ultra-fine powder that's suspended in liquid. If you want to know exactly what's in these inks, good luck to you. Inkjet cartridges are a huge revenue generator for printer companies, and they carefully guard their formulas. Laser printing technology isn't quite as straightforward. That's because toner doesn't adhere to paper the way that a liquid-based ink does. Toner is made up mostly of finely ground polyester, which is a type of plastic. Like your slacks sticking to your legs, polyester powder can hold a static charge that grabs onto anything with an opposite charge. In these printers, a laser creates an electrostatic template of your desired images on a rotating metal drum, which has an electrical charge. A cartridge dispenses toner onto the drum, but the toner sticks only to certain places — such as the outline of your kitty's soft belly — where the laser alters the drum's electrical charge. Fittingly, the printer also charges the sheets of paper as they pass through the machine. As the sheet curls past the drum, it pulls off the charged toner in exact shapes that make up text and images. Then a hot fuser basically melts the polyester in place, making sharp, smudge-free prints.

How hot do printers get?

functional groups

Hydroxyl (OH) - Oxygen is bound to carbon on one side and singly bound to a hydrogen on the other side. Hydroxyl groups are polar since the oxygen hogs the electrons it is supposed to be sharing with hydrogen. This hogging means that any organic compound with a hydroxyl group will have polar areas. Do not get this functional group confused with the hydroxide ion (OH-), which is a negatively charged unit. Carbonyl (ACHOB) - Oxygen is doubly bound to carbon (C=O). Depending on where the doubly bound oxygen occurs along the carbon backbone, you can get totally different classes of sugars. If the doubly bound oxygen is at the end of the carbon chain, it forms an aldehyde (RCHO). If the doubly bound oxygen attached to any other carbon, the sugar is a ketone (RCOR'). Carboxyl (RCOOH) - A carbon is bound to two oxygens. One oxygen forms a double bond with the carbon (C=O), and the other forms a single bond (C-O). The oxygen with a single bond is also bound to a hydrogen (O-H or OH). Carboxyl groups are characteristic of fatty acids and are what allow three fatty acids to bind to a molecule of glycerol, which produces a triglyceride. Carboxyl is also one of the functional groups comprising an amino acid. Amino (CNH2) - A nitrogen is singly bound to two hydrogens (N-H) and singly bound to a carbon (N-C). This functional group is found in amino acids, hence the name. Phosphate (H2PO4R) - A phosphorous atom is singly bound to three oxygens (P-O) and doubly bound to one more oxygen (P=O). Two of the singly bound oxygens have a hydrogen attached, making -OH depending on pH conditions. The last singly bound oxygen is bound to a carbon (C-O). Phosphates form the polar "head" of the phospholipids and form part of the "backbone" of nucleic acids.

Hypoxanthine

Hypoxanthine is a naturally occurring purine derivative. It is occasionally found as a constituent of nucleic acids, where it is present in the anticodon of tRNA in the form of its nucleoside inosine. It has a tautomer known as 6-hydroxypurine. Hypoxanthine is a necessary additive in certain cell, bacteria, and parasite cultures as a substrate and nitrogen source. For example,[1][2] it is commonly a required reagent in malaria parasite cultures, since Plasmodium falciparum requires a source of hypoxanthine for nucleic acid synthesis and energy metabolism. It is one of the products of the action of xanthine oxidase on xanthine. However, more frequently in purine degradation, xanthine is formed from oxidation of hypoxanthine by xanthine oxidoreductase. Hypoxanthine-guanine phosphoribosyltransferase converts hypoxanthine into IMP in nucleotide salvage. Hypoxanthine is also a spontaneous deamination product of adenine. Because of its resemblance to guanine, the spontaneous deamination of adenine can lead to an error in DNA transcription/replication, as it base pairs with cytosine. Hypoxanthine is removed from DNA by base excision repair, initiated by N-methylpurine glycosylase (MPG), also known as alkyl adenine glycosylase (Aag).

glycolysis with ATP synthase

In a process called glycolysis, which occurs in the cytoplasm just outside the mitochondrion, electrons are stripped from glucose and passed through the outer mitochondrial membrane into the intermembrane space. Here, the electrons are passed to a series of special proteins embedded in the IMM. As the electrons move from one membrane protein to the next, energy is released and protons (hydrogen ions, or H+) in the matrix are pumped across the IMM and into the intermembrane space. Fairly quickly, a large number of protons accumulate in the intermembrane space and, like water behind a dam, exert great pressure on the IMM. Luckily for them, and life as we know it, there is a special protein complex embedded in the IMM that allows protons to flow back into the matrix. The special part about this channel protein complex is that it is capable of harnessing the enormous energy produced by the rush of protons. Exactly like a turbine in a dam, ATP synthase—as this protein complex is named, and yes, it is an enzyme (-ase)—has a rotor that spins when protons push past. Can't visualize what we mean? Here's a picture: The energy generated by the turning of the rotor is converted into ATP, just like the energy made by turning a water turbine in a dam is converted into electricity. In this way, one molecule of glucose can be converted into about 38 molecules of ATP. A pretty good investment, if you ask us. This awesome process is called cellular respiration, and it is all made possible by the mitochondrial membranes! The mitochondrial membrane is the site of ATP synthesis, and the ATP made is inside the mitochondrion. How do you think it gets to the cytoplasm so that it can be used? Naturally, it gets where it needs to go by using those transmembrane channels we discussed earlier.

ice line astronomy

In astronomy or planetary science, the frost line, also known as the snow line or ice line, is the particular distance in the solar nebula from the central protostar where it is cold enough for volatile compounds such as water, ammonia, methane, carbon dioxide, carbon monoxide to condense into solid ice grains.

how many tons are added to earth each year from meteors?

In fact from satellite observations of meteor trails it's estimated that about 100 - 300 metric tons (tonnes) of material strikes Earth every day. That adds up to about 30,000 to 100,000 tonnes per year.

Plasmon

In physics, a plasmon is a quantum of plasma oscillation. Just as light (an optical oscillation) consists of photons, the plasma oscillation consists of plasmons. The plasmon can be considered as a quasiparticle since it arises from the quantization of plasma oscillations, just like phonons are quantizations of mechanical vibrations. Thus, plasmons are collective (a discrete number) oscillations of the free electron gas density. For example, at optical frequencies, plasmons can couple with a photon to create another quasiparticle called a plasmon polariton.

What Is Photosynthesis?

In the first phase of photosynthesis, cellular protein pigments called chloroplasts are excited by light that propels them into high-energy states. The chloroplasts then transfer this energy through electrons to other protein complexes (read: several proteins stuck together). This group of proteins is called the electron transport chain. The proteins operate similarly to a group of dominoes: after the first one has been pushed, each protein transfers energy to each member along down the line. Water (H2O) is split in this process, releasing oxygen (O2) and hydrogen ions (H+). The electrons from the electron transport chain combine with these H+ ions and nicotinamide adenine dinucleotide phosphate ions (NADP+) to form adenosine triphosphate (ATP) and a reduced unit of NADP+, called NADPH (NADP plus an electron, or H). These energy storage forms, ATP and NADPH, are used to convert carbon dioxide (CO2) to build carbohydrates during the second phase of photosynthesis. Plants can then break down these carbohydrates to fuel their existence. We see plant leaves as green. We bet you know why, too. That's right—plants absorb all wavelengths of visible light except green. Certain molecules, called pigments, have the ability to absorb specific wavelengths of light. Chlorophylls are the pigments that make photosynthesis happen. There are several types of chlorophylls, and rather than giving them flashy names like Diana, Vince, and Una, scientists just named them a, b, and c. Chlorophyll a is the important one, as it is the molecule that's found in all plants, algae, and photosynthetic cyanobacteria. Chlorophyll b is found in plants and algae (though in far smaller quantities compared to chlorophyll a), and chlorophyll c is only found in some species of kelp, diatoms, and dinoflagellates. When a chlorophyll molecule absorbs light energy, its electrons are excited to a high-energy state—like, "just got the latest iPhone" excited. Just like for anyone, that energy boost to the chlorophyll is shocking, and all that energy needs to go somewhere. While we might use our newfound energy to study for a biology exam, the pigments (which don't need to study since they already know the steps of photosynthesis) let go of that energy in the form of heat or light.zWe see plant leaves as green. We bet you know why, too. That's right—plants absorb all wavelengths of visible light except green. Certain molecules, called pigments, have the ability to absorb specific wavelengths of light. Chlorophylls are the pigments that make photosynthesis happen. There are several types of chlorophylls, and rather than giving them flashy names like Diana, Vince, and Una, scientists just named them a, b, and c. Chlorophyll a is the important one, as it is the molecule that's found in all plants, algae, and photosynthetic cyanobacteria. Chlorophyll b is found in plants and algae (though in far smaller quantities compared to chlorophyll a), and chlorophyll c is only found in some species of kelp, diatoms, and dinoflagellates. When a chlorophyll molecule absorbs light energy, its electrons are excited to a high-energy state—like, "just got the latest iPhone" excited. Just like for anyone, that energy boost to the chlorophyll is shocking, and all that energy needs to go somewhere. While we might use our newfound energy to study for a biology exam, the pigments (which don't need to study since they already know the steps of photosynthesis) let go of that energy in the form of heat or light. When it comes to photosynthesis, the mesophyll cells are where the magic happens (meso- means "middle," and the mesophyll is found inside the leaves, under the upper epidermis). Gases such as CO2 and O2 enter and exit the leaves through special openings called stomata. Mesophyll cells house the chloroplasts, the HQ for photosynthesis. Chloroplasts have an inner and outer membrane (remind you of anyone? Two membranes aren't just for mitochondria). And guess what's inside the inner membrane...yup, another membrane. Structures called thylakoids are bound together with a membrane like cute little macaroons. The French ones, not those weird coconut thingies. The thylakoids are coated with chlorophyll molecules to collect sunlight for photosynthesis and float in a fluid called stroma, which contains all the necessary enzymes for converting carbon dioxide (CO2) into organic molecules. Like mitochondria, the chloroplasts are unique organelles because they contain their own DNA. This DNA encodes for many of the proteins used in photosynthesis, although the cell's nuclear DNA also encodes for some of the needed proteins, too. The chloroplast's DNA is excellent evidence for its evolutionary origin as a single-celled photosynthetic organism. Photosynthesis occurs in two stages: light-dependent reactions and light-independent reactions. In the light-dependent reactions, this energy is captured and transferred from one molecule to another, down an electron transport chain, in turn creating the cell's energy boost, the molecules adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH). That's right, two important molecules with two even longer names. Don't worry about memorizing those tongue twisters, though. As long as you remember their abbreviations, that's good enough. The outputs from the light-dependent reactions are used in the light-independent reactions to fuel the production of carbohydrates. • Light reactions occur in the thylakoid membrane Inputs: water (H2O) and light Outputs: Oxygen (O2) and energy (ATP and NADPH) Light-independent reactions occur in the stroma Inputs: ATP and NADPH (from the light reactions) and CO2 Outputs: carbohydrates

The Light-Dependent and Light-Independent Reactions

In the light-dependent reactions of photosynthesis, the energy from light propels the electrons from a photosystem into a high-energy state. In plants, there are two photosystems, aptly named Photosystem I and Photosystem II, located in the thylakoid membrane of the chloroplast. The thylakoid membrane absorbs photon energy of different wavelengths of light. Even though the two photosystems absorb different wavelengths of light, they work similarly. Each photosystem is made of many different pigments. Some of these pigments can be described as absorption pigments, and others are considered action pigments. The absorption pigments transfer the energy from sunlight to another pigment; at each transfer, the absorption pigments pass the photon energy to another pigment that absorbs a similar or lower wavelength of light. Remember when we said that light is funky and acts like it has both particles and waves? A photon is what we call the particle-like aspect of light. In other words, a photon is the basic unit of light. Anyway, eventually, the energy makes it to the reaction center, or action pigment. At this point, the photosystem loses a highly charged electron to adjacent oxidizing agents, or electron acceptors, in the electron transport chain. This transfer all occurs mind-bogglingly quickly at an estimated time of 200 × 10-12 seconds! Weed killers called herbicides work by targeting enzymes used in the light reactions of photosynthesis. Come here, little chloroplasts.

Golgi apparatus

In these membranous stacks, called cisternae, proteins that have been marked for secretion in the RER are packaged into vesicles that transport them to the plasma membrane where they are secreted from the cell. The Golgi body also packages the lipids and steroids made in the SER into vesicles. Packaged lipids and steroids are transported to the edge of the cell, as well as to all organelles within the cell, where they are used to build or repair the cell and organelle membranes. Just remember that the Golgi body likes sticking things into vesicles. In a way, it's like UPS, except that the Golgi body is 75% less likely to chuck, crush, or lose your packages. Lastly, small portions of the Golgi body cisternae often bud off into small spheres to create lysosomes. Inside a cell, numerous organelles function to remove wastes. One of the key organelles involved in digestion and waste removal is the lysosome. Lysosomes are organelles that contain digestive enzymes. They digest excess or worn out organelles, food particles, and engulfed viruses or bacteria.

Did animals co-evolve to fit species specific aesthetic appeals?

Is what we view animals as today a genetically curated version of what animals decided is quintessence of beauty for their respective species? Not sure if we will ever have an adequate answer for this. It seems as if it does play a significant role in how species choose mates.

when was pompeii?

Its most famous eruption took place in the year 79 A.D., when the volcano buried the ancient Roman city of Pompeii under a thick carpet of volcanic ash.

Serious question though, do you think Goggins genuinely challenges himself physically as an escape from dealing with the real issues at hand?

Just another escape mechanism wearing a new mask.

Chloroplast Membranes

Just like in mitochondria, the membranes of the chloroplast provide the basis for chloroplast function. Unlike mitochondria, chloroplasts have three phospholipid bilayers. And you thought a double bilayer was complicated! The outer two membranes are similar in structure and orientation to the nuclear membranes: there is an outer membrane, an inner membrane, and a very small space between them called the—you guessed it!—intermembrane space. The third chloroplast membrane is arranged in discs called thylakoids. These discs are stacked on top of each other in structures called grana (singular granum) that look a lot like little stacks of green casino chips. Not that you spend any time in casinos, or gambling, for that matter. Each chloroplast contains many, many grana. The space between the inner chloroplast membrane and the grana is called the stroma. The space inside the thylakoid discs is called the lumen, or, more specifically, the thylakoid lumen. The work of the chloroplast takes place in the stroma, the lumen, and, most importantly, in the thylakoid membrane itself. Here, the light-capturing green pigment chlorophyll is held in place by membrane proteins. Chlorophyll converts the energy from the sun into electrical energy. This electrical energy is then passed from one membrane protein to another, providing the power to pump protons from the stroma into the thylakoid lumen. Just like in the mitochondria, the protons (hydrogen ions, or H+) rush back across the membrane into the stroma, and ATP synthase, an enzyme, converts the generated energy into ATP. At this point, ATP and other products produced by the thylakoid membrane proteins are combined with molecules of carbon dioxide (CO2) in the stroma to make glucose. The whole elaborate process, from sunlight to glucose, is called photosynthesis. In plant mitochondria, the glucose made in photosynthesis is converted into ATP, which plant cells use to grow, survive, and reproduce. Ultimately, the energy contained in this glucose is used by the animals who eat plants, or by the animals who eat the animals who eat the plants. It is then converted back into CO2, at which point plants can turn it back into glucose and so on. Forget The Lion King: the real circle of life starts and ends in the membranes of chloroplasts. There are many photosynthetic plants, but have you heard of a photosynthetic animal? There is one that steals and uses the chloroplasts of the algae it consumes. Shaped like a leaf itself, the slug Elysia chlorotica already has a reputation for kidnapping the photosynthesizing organelles and some genes from algae. Now it turns out that the slug has acquired enough stolen goods to make an entire plant chemical-making pathway work inside an animal body. The slugs can manufacture the most common form of chlorophyll, the green pigment in plants that captures energy from sunlight, Pierce reported January 7 at the annual meeting of the Society for Integrative and Comparative Biology. Pierce used a radioactive tracer to show that the slugs were making the pigment, called chlorophyll a, themselves and not simply relying on chlorophyll reserves stolen from the algae the slugs dine on. "This could be a fusion of a plant and an animal — that's just cool," said invertebrate zoologist John Zardus of The Citadel in Charleston, S.C. Microbes swap genes readily, but Zardus said he couldn't think of another natural example of genes flowing between multicellular kingdoms. Pierce emphasized that this green slug goes far beyond animals such as corals that host live-in microbes that share the bounties of their photosynthesis. Most of those hosts tuck in the partner cells whole in crevices or pockets among host cells. Pierce's slug, however, takes just parts of cells, the little green photosynthetic organelles called chloroplasts, from the algae it eats. The slug's highly branched gut network engulfs these stolen bits and holds them inside slug cells. Some related slugs also engulf chloroplasts but E. chlorotica alone preserves the organelles in working order for a whole slug lifetime of nearly a year. The slug readily sucks the innards out of algal filaments whenever they're available, but in good light, multiple meals aren't essential. Scientists have shown that once a young slug has slurped its first chloroplast meal from one of its few favored species of Vaucheria algae, the slug does not have to eat again for the rest of its life. All it has to do is sunbathe.

Cell Wall

Like the cell walls in bacteria, fungi, algae, and some archaea, plant cell walls are found just outside the plasma membrane and provide the cells structure and protection. The cell wall prevents plant cells from bursting (lysing) when too much water moves into the cell across the membrane. As water pushes against the cell wall from the inside, plant cells become large and firm because pressure, known as turgor pressure, builds up against the inside of the cell wall. You have experienced the presence of turgor pressure when you have broken a piece of crisp celery. In the same way, if you have ever tried to break a piece of wilted celery, you also know what effect the absence of turgor pressure can have on a plant. Plant cell walls also have small openings, called plasmodesmata, that allow cells to communicate with adjacent cells. Plant cell walls are composed primarily of a protein called cellulose, while fungal cell walls are made of a protein called chitin. Chitin is the polysaccharide made up of N-acetyl-D-glucosamine monomers. The basic structure of chitin is similar to that of cellulose. The main function of chitin is to provide strength and support to the fungal cell wall. Moreover, chitin is the main structural component of the exoskeleton of arthropods such as insects and crustaceans. Chitin occurs in the radulae of mollusks, the beak of cephalopods, and the scales of fish as well. Chitin is used in the sizing and strengthening of paper and as a food thickener and stabilizer. Cellulose is a polysaccharide made up of D-glucose monomers. It is the most abundant type of macromolecule on earth, making up of the plant and algal cell wall. Since the D-glucose monomers form β-(1→4)-linkages, cellulose is a linear polymer. The parallel-aligned polymers of cellulose form microfibers that are bound together by hydrogen bonds. There are around 80 cellulose molecules in a microfiber. These fibers are cross-linked with hemicellulose. Both cellulose and hemicellulose occur suspended in the middle lamella of the cell wall. The strength of the chitin polymer matrix is higher due to the increased hydrogen bonding capacity while the strength of the cellulose polymer matrix is comparatively low. Therefore, chitin provides more rigidity to the structures than the cellulose does. Chitin developed later and cellulose developed earlier.

Lipids

Lipids are an eclectic bunch of biomolecules. Yet, for all their differences, each and every lipid is hydrophobic, meaning it doesn't dissolve in water. That's because long stretches of lipid molecules only have carbons and hydrogens in them. Carbon and hydrogen share electrons equally, and both carbon-carbon bonds (C-C) and carbon-hydrogen bonds (C-H) are nonpolar / hydrophobic / water-phobic / well, you get the idea. Remember, water is a polar snob. Since the feeling is mutual, long stretches of nonpolar lipids will remain undissolved in water. The monomer for lipids is a fatty acid, or a long string of carbons and hydrogens with a carboxyl group at the end. A carboxyl group is a chemical group—everyone loves those—based around a central carbon that has four bonds (as carbon tends to do). Two of the bonds are stuck to one oxygen (C=O). The third bond is stuck to a hydroxyl group (C-OH), and the last bond forms with...some other atom. This atomic "friend" is usually called A or R, so it can remain anonymous. Fatty acids can be saturated or unsaturated. Remember, carbons are friendly; they can bind to up to four other atom friends. If every single carbon in a fatty acid is singly bound to four friends, whether they be carbons or hydrogens, then that fatty acid has totally maximized its bonding potential. Score. We say that it is saturated. If, on the other hand, a carbon double bonds to another carbon, then it can only form single bonds with two other atom friends. Therefore, carbon now has only three friends in total. We call a fatty acid like this unsaturated, because carbon has not maximized its friending, erm, bonding potential. Notice that when two carbons form a double bond, it causes a little bend in the fatty acid chain. The difference between a fat and an oil basically comes down to the amount of unsaturation in the fatty acids. Saturated fatty acids form straight chains; therefore, triglycerides with saturated fatty acids can pack really close together. A bit like screaming tweens at a Miley Cyrus concert. These fats tend to be solid at room temperature. When there are some unsaturated fatty acids thrown into the mix, the chains get all kinky and bent out of shape, and triglycerides can't pack in as tightly. This looks more like the concert of a washed-up, one-hit wonder. Mmm...Vanilla Ice, anyone? Oils are the result of living in unsaturated fat country, like olive, canola, or sesame. Note that all of these are liquids at room temperature. Fats and oils store a ton of energy. At 9.3 Calories per gram (capital C), they store over twice as much energy as carbs or proteins, both of which only yield about 4.1 Calories per gram. Per unit weight, fats are clearly a more efficient way to keep energy for long-term use. Waxes are like fats in that they are solid at room temperature. This solidity is due to their high degree of saturation, but waxes tend to be used for functions other than energy storage, like waterproofing leaves and fur or making floors shiny.

Louse

Louse (plural: lice) is the common name for members of the order Phthiraptera, which contains nearly 5,000 species of wingless insect. Lice are obligate parasites, living externally on warm-blooded hosts which include every species of bird and mammal, except for monotremes, pangolins, and bats. Lice are vectors of diseases such as typhus. Nearly 5,000 species of louse have been identified, about 4,000 being parasitic on birds and 800 on mammals. Dog lice do not like to infest humans. Most lice are quite species-specific; that is, dog lice like dogs and people lice like people. It is definitely possible for a dog louse to get on a person, and it might even bite or try to feed, but it will not set up an infestation. The three species of sucking lice that parasitize human beings belong to two genera, Pediculus and Pthirus: head lice (Pediculus humanus capitis), body lice (Pediculus humanus humanus), and pubic lice (Pthirus pubis).

Lysosomes

Lysosomes are small spheres of phospholipids made by the Golgi bodies and are responsible for breaking down cellular debris and material taken into the cell through the process of phagocytosis (the cell's swallowing up of things). The interior of a lysosome contains many enzymes and is slightly acidic, so material can be digested without harming the rest of the cell. Lysosomes maintain their acidity by pumping protons (hydrogen ions, or H+ ions) across their membranes through integral channel proteins. Helpful tip: when you see lys- as part of a word, think of cutting, chopping, or breaking down. Lysosomes chop things up, glycolysis is the breaking down of sugar, and so on. There is a method to this wordy madness.

Different types of stars

Main Sequence stars, White Dwarfs, Red Giants, Red Supergiants.

How to tell a meteorite is from Mars?

Martian meteorites are distinguished from Earth rocks and other meteorite types by their chemical and mineral composition, as well as their age. Moreover, gases trapped in shock glass in martian meteorites have been matched to measurements of the martian atmosphere taken by the NASA Viking mission in 1976.

What happened after the Yucatan impact?

Mathematical models indicate that a major impact would eject huge amounts of pulverized rock high above the atmosphere. As this material fell back, Earth's atmosphere would be turned into a glowing oven of red-hot meteorites streaming through the air, and the heat would trigger massive forest fires around the world. Soot from such fires has been found in the final Cretaceous clay layers. Once the firestorms cooled, the remaining dust in the atmosphere would block Sunlight and produce deep darkness for a year or more, killing off most plant life. Other effects, such as acid rain and enormous tsunamis (tidal waves), are also predicted by the models. Geologists have located a crater at least 180 km (110 mi) in diameter centered near the village of Chicxulub (pronounced CHEEK-shoe-lube) in the northern Yucatán region of Mexico (Figure 8-11c). Although the crater is completely covered by sediments, mineral samples show that it contains shocked quartz typical of impact sites and that it is the right age. The impact of an object 10 to 15 km (6 to 10 mi) in diameter formed the crater about 65 million years ago, just when the dinosaurs and many other species died out. Most Earth scientists now consider this to be the scar of the impact that ended the Cretaceous period.

How to determine the age of a star?

Mathematical models of what the star is composed of, its mass, its gravitational pull, which will tell you its stage in evolution. Essentially, astronomers determine the age of stars by observing their spectrum, luminosity and motion through space. They use this information to get a star's profile, and then they compare the star to models that show what stars should look like at various points of their evolution.

oldest piece of architecture

Megalithic Temples of Malta Dating back to 3,500 to 2,500 BCE, the Megalithic Temples of Malta are some of the oldest structures in the world. As the name suggests, they are a group of stone temples older than Stonehenge and the Egyptian pyramids.

meteorite word origin

Meteor (streak of light) + ite (rock/lithos) = rock made of a streak of light

Mesoamerica

Mexico and Central America "Middle America" the region extending from modern-day Mexico through Central America

mitochondria and chloroplasts used to be bacteria

Mitochondria and chloroplasts were actually prokaryotes themselves, simple bacteria that formed a relationship with host cells. These host cells were prokaryotes that were unable to live in oxygen-rich environments and engulfed these mitochondrial precursors. Since the symbiotic hypothesis states that mitochondria and chloroplasts arose from bacteria entering a eukaryotic cell to form a symbiotic relationship, similarities between bacteria and these semiautonomous organelles show strong evidence that this hypothesis is correct. Mitochondria share very similar characteristics with purple-aerobic bacteria. They both use oxygen in the production of ATP, and they both do this by using the Kreb's Cycle and oxidative phosphorylation. (mitochondria on the left and purple aerobic bacteria on the right) Chloroplasts are very similar to photosynthetic bacteria in that they both have very similar chlorophyll that harness light energy to convert into chemical energy. (Chloroplast on the left and photosynthetic bacteria on the right) Although there are many similarities between mitochondria and purple aerobic bacteria and chloroplasts and photosynthetic bacteria, they appear to be slight and to have arisen via evolution. Size of mitochondria and chloroplasts in comparison to bacteria is another simple observation that supports the endosymbiotic hypothesis. Mitochondria, chloroplasts, and prokaryotes (bacteria) range from about one to ten microns in size. (1 micron=1X10^-6 Meters) This seems very basic, but if there was a large difference in sizes between these three components, the hypothesis would appear to be false. The first piece of evidence that needed to be found to support the endosymbiotic hypothesis was whether or not mitochondria and chloroplasts have their own DNA and if this DNA is similar to bacterial DNA. This was later proven to be true for DNA, RNA, ribosomes, chlorophyll (for chloroplasts), and protein synthesis. This provided the first substantial evidence for the endosymbiotic hypothesis. It was also determined that mitochondria and chloroplasts divide independently of the cell they live in. Mitochondria having their own DNA and dividing independently of the cell is what ultimately results in only mitochondrial DNA being inherited by one's mother since only an egg cell has DNA while a sperm cell does not. (This relationship also further proves that the discovered characteristics of mitochondria are true.) This level of independence among semiautonomous organelles shows that they are not very related to the nucleus or other organelles of a eukaryotic cell. Since they are not related, it appears to be even more probable that mitochondria and chloroplasts were originally bacteria that entered the eukaryotic cell via endocytosis to form a symbiotic relationship. Scientists (particularly Lynn Margulis) then began to think that if mitochondria and chloroplasts were truly bacteria that were taken into eukaryotic cells via endocytosis, then there must be a historical drive to promote this symbiotic relationship. About 3.8 billion years ago, there were only anaerobic bacteria in existence because Earth's atmosphere did not contain any oxygen. The first photosynthetic bacteria arose around 3.2 billion years ago and began producing large quantities of oxygen as a byproduct of photosynthesis. Oxygen is very toxic to cells, and as a result, these anaerobic, photosynthetic bacteria became less effective at surviving in their environment. At this point, some of the anaerobic bacteria evolved into aerobic bacteria. Aerobic bacteria are much better suited to this oxygen containing environment and they even use oxygen in the process of making ATP (a molecule that stores a great amount of easily accessible energy). One important factor that both of these bacteria lacked was the ability to ingest large quantities of nutrients from the surrounding environment via phagocytosis. About 1.5 billion years ago, the first nucleated cell (the eukaryote) was arose through evolution, and this cell had the groundbreaking ability to take in large quantities of nutrients via phagocytosis. The fact that bacteria, which are very similar to mitochondria and chloroplasts, existed before the eukaryotic cell shows evidence that it was bacteria that was integrated into a eukaryotic cell rather than eukaryotes being entirely separate in evolutionary history. This timeline also gives evidence as to why a symbiotic relationship would be beneficial. More: https://endosymbiotichypothesis.wordpress.com/evidence-for-the-endosymbiotic-hypothesis/

mitochondria vs chloroplast

Mitochondria are present in the cells of all types of aerobic organisms like plants and animals, whereas Chloroplast is present in green plants and some algae, protists like Euglena. ... The inner membrane of mitochondria is folded into cristae while that of a chloroplast, rises into flattened sacs called as thylakoids

What processes take place in mitochondria and chloroplasts? How do the products of these processes relate to each other?

Mitochondria convert sugars into ATP and CO2 through the process of cellular respiration. Chloroplasts convert CO2 into sugars through the process of photosynthesis. The products of one process become the reactants of the next in the great "circle of life."

Mitochondrial Membranes

Mitochondria, like nuclei, have two phospholipid bilayers. The bilayer closest to the cytoplasm, or the outer mitochondrial membrane (OMM, not Om Nom Nom), has integral proteins called porins that allow small molecules to pass freely into the mitochondria. These molecules do not get very far, though, because they soon encounter the second bilayer, or inner mitochondrial membrane (IMM). This membrane is folded and twisted throughout the mitochondrion into structures called cristae, much like all 25 feet of your small intestine is twisted and folded throughout your abdomen. The space inside the IMM is called the matrix, while the space between the two mitochondrial membranes is cleverly named the intermembrane space. Since the OMM has many porins, the intermembrane space closely resembles the physical and chemical properties of the cytoplasm. As you may, and should, recall from the section on mitochondria, these organelles are chiefly responsible for converting the chemical energy in macromolecules, like glucose, into molecules of ATP, adenosine triphosphate, that can be used by the cell for energy. The ability of a mitochondrion to convert glucose and ADP, adenosine diphosphate, into ATP is intricately connected to the structure of the mitochondrial membranes. In a process called glycolysis, which occurs in the cytoplasm just outside the mitochondrion, electrons are stripped from glucose and passed through the outer mitochondrial membrane into the intermembrane space. Here, the electrons are passed to a series of special proteins embedded in the IMM. As the electrons move from one membrane protein to the next, energy is released and protons (hydrogen ions, or H+) in the matrix are pumped across the IMM and into the intermembrane space. Fairly quickly, a large number of protons accumulate in the intermembrane space and, like water behind a dam, exert great pressure on the IMM. Luckily for them, and life as we know it, there is a special protein complex embedded in the IMM that allows protons to flow back into the matrix. The special part about this channel protein complex is that it is capable of harnessing the enormous energy produced by the rush of protons. Exactly like a turbine in a dam, ATP synthase—as this protein complex is named, and yes, it is an enzyme (-ase)—has a rotor that spins when protons push past. Can't visualize what we mean? Here's a picture: The energy generated by the turning of the rotor is converted into ATP, just like the energy made by turning a water turbine in a dam is converted into electricity. In this way, one molecule of glucose can be converted into about 38 molecules of ATP. A pretty good investment, if you ask us. This awesome process is called cellular respiration, and it is all made possible by the mitochondrial membranes! The mitochondrial membrane is the site of ATP synthesis, and the ATP made is inside the mitochondrion. How do you think it gets to the cytoplasm so that it can be used? Naturally, it gets where it needs to go by using those transmembrane channels we discussed earlier.

Large Central Vacuole

Most plant cells have a large membrane-bound sac called a vacuole. This vacuole can occupy between 30% and 80% of the total volume of the cell, making it the largest single cellular structure. The main function of the large central vacuole is to help the cell maintain water pressure—again, known as turgor pressure—on the cell wall. Water molecules flow into the central vacuole, and like a big balloon inside a cardboard box, it fills up and pushes outward on the cell wall. Helpful tip: the word "vacuole" sounds a lot like vacant or vacuum, and this is a good way to think about this organelle. It mostly contains a water-based solution with some organic compounds and enzymes, but is otherwise empty.

Will a GFCI protected outlet trip if you drop a hair dryer in a porcelain sink?

No. It will not notice a change in current flow since the sink is nonconductive and therefore it will not trip. GFCI's can measure differences as small as 4 milliamps.

Do all prokaryotic cells eat food?

No. Many prokaryotic cells are capable of making their own food through the process of photosynthesis. The most common photosynthesizing prokaryotes are called cyanobacteria. These amazing single-celled organisms convert energy from the sun into energy that is used to turn CO2 into sugar.

Marie Curie

Notable female Polish/French chemist and physicist around the turn of the 20th century. Won two nobel prizes. Did pioneering work in radioactivity. Curie won two Nobel Prizes, for physics in 1903 and for chemistry in 1911. She was the first woman to win a Nobel Prize as well as the first person—man or woman—to win the prestigious award twice. She remains the only person to be honored for accomplishments in two separate sciences. Her daughter went on to win a nobel prize: Irène Joliot-Curie was a French chemist, physicist, and a politician with Polish ancestry, the daughter of Marie Curie and Pierre Curie and the wife of Frédéric Joliot-Curie. Jointly with her husband, Joliot-Curie was awarded the Nobel Prize in Chemistry in 1935 for their discovery of artificial radioactivity. 66 years old

Nucleic Acids

Nucleic acids—our buddies deoxyribonucleic acid, or DNA, and ribonucleic acid, or RNA—consist of long chains of nucleotides, which are monomers. (Sensing a pattern yet? Good. Biology is all about patterns.) Every nucleotide has three parts: A sugar A phosphate group A nitrogen-containing base In DNA, the sugar is deoxyribose (-ose means "sugar"), and in RNA, the sugar is ribose. Hence the "D" and "R" in DNA and RNA. Both of these sugars have five carbons. In fact, the only difference between them is that ribose has an extra hydroxyl group (OH), and deoxyribose just has a hydrogen in the same spot. De- plus oxy- means "without oxygen." Do you remember that in amino acids the mysterious R group varied and gave each amino acid its unique identity? In a nucleic acid, the nitrogen-containing base plays the same role as the R group. Deoxyribose can bind to four different Rs, or kinds of nitrogen-containing bases. Here they are in all their glory: Adenine, or A Guanine, or G Cytosine, or C Thymine, or T Therefore, the four bases of RNA are: Adenine, or A Guanine, or G Cytosine, or C Uracil, or U Nucleotides bind together by—say it with us—dehydration synthesis. Shocking! A hydrogen from the phosphate (-H2PO4R) group of one nucleotide combines with a hydroxyl group (-OH) from the sugar of another nucleotide. Water is produced, and the two nucleotides are officially stuck to each other. When lots of these bonds form, we wind up with a long chain of nucleotides; therefore, the "backbone" of this chain consists of alternating sugars and phosphates. RNA is single stranded, meaning it has one linear chain and the nitrogen-containing bases aren't bound to anything else. In contrast, DNA is double stranded; each base binds to another base, which, of course, is part of its own nucleotide. A helpful tip for remembering this is to realize that "double stranded" and "DNA" both start with the letter D. The result is a double-stranded molecule. DNA looks like a ladder when it is all stretched out, but coils into a spiral, or helix, under normal conditions. This is the reason that DNA is called a double helix. Adenine (A) and thymine (T) always pair together (A-T), while cytosine (C) and guanine (G) always pair together (C-G). In other words, A and T are complementary bases, as are C and G. The sequence of nucleotides in DNA provides information that is later used to make proteins. Proteins, as you already know, have many different functions and are critical to building organisms. DNA is like a really, really long instruction book. D is for directions. On the other hand, RNA translates the DNA message to a format that can be read by ribosomes, the cellular organelles that assemble proteins. RNA also plays a role in recruiting the correct amino acids to the protein assembly sites. When organisms reproduce, their DNA is copied and passed on to their offspring, ensuring that every living organism has a master copy of the instruction book.

Which types of cells have cell walls?

Plants are not the only organisms whose cells have a wall. Many bacteria and archaea also have cell walls. These walls usually differ slightly, though sometimes majorly, from those commonly seen surrounding plant cells. Just because something has a cell wall does not automatically make it a plant cell.

Plasma oscillation

Plasma oscillations, also known as Langmuir waves (after Irving Langmuir), are rapid oscillations of the electron density in conducting media such as plasmas or metals in the ultraviolet region. The oscillations can be described as an instability in the dielectric function of a free electron gas. The frequency only depends weakly on the wavelength of the oscillation. The quasiparticle resulting from the quantization of these oscillations is the plasmon.

how much mass the sun emits each day?

Plugging and chugging: mass = 4 x 10^33 / 9 x 10^20 = 4.4 x 10^12 grams per second, or more than 4 million tons per second. So there you go. The Sun loses 4 million tons of mass per second due to fusion. It contains 99.86% of all of the mass of the entire Solar System. The Sun is 864,400 miles (1,391,000 kilometers) across. This is about 109 times the diameter of Earth. The Sun weighs about 333,000 times as much as Earth.

polonium uses

Po can be used as an atomic heat source, but because of the isotope's short half-life (138.4 days), it doesn't provide power for long-term uses. Polonium is also used in anti-static brushes to eliminate dust on photographic film. It is sealed in brushes to control the radioactive emissions.

Prokaryotic vs. Eukaryotic

Prokaryotes are organisms made up of cells that lack a cell nucleus or any membrane-encased organelles. Eukaryotes are organisms made up of cells that possess a membrane-bound nucleus that holds genetic material as well as membrane-bound organelles.

Prokaryotic Plasma Membrane

Prokaryotic cells can have multiple plasma membranes. Prokaryotes known as "gram-negative bacteria," for example, often have two plasma membranes with a space between them known as the periplasm. As in all cells, the plasma membrane in prokaryotic cells is responsible for controlling what gets into and out of the cell. A series of proteins stuck in the membrane (poor fellas) also aids prokaryotic cells in communicating with the surrounding environment. Among other things, this communication can include sending and receiving chemical signals from other bacteria and interacting with the cells of eukaryotic organisms during the process of infection. Infection, by the way, is the kind of thing that you don't want prokaryotes doing to you. Keep in mind that the plasma membrane is universal to all cells, prokaryotic and eukaryotic.

Prokaryotic Ribosomes

Prokaryotic ribosomes are smaller and have a slightly different shape and composition than those found in eukaryotic cells. Bacterial ribosomes, for instance, have about half of the amount of ribosomal RNA (rRNA) and one-third fewer ribosomal proteins (53 vs. ~83) than eukaryotic ribosomes have3. Despite these differences, the function of the prokaryotic ribosome is virtually identical to the eukaryotic version. Just like in eukaryotic cells, prokaryotic ribosomes build proteins by translating messages sent from DNA.

Etruscan civilization

Prospered between 950 and 300 BCE, was located between the Arno River in Pisa and Florence; and the Tiber River in Rome (Northwestern Italy). Literary and historical texts in the Etruscan language have not survived, making modern understanding of their society and culture heavily dependent on much later and generally disapproving Roman and Greek sources.

Protease inhibitor

Protease inhibitors (PIs) are a class of antiviral drugs that are widely used to treat HIV/AIDS and hepatitis C. Protease inhibitors prevent viral replication by selectively binding to viral proteases (e.g. HIV-1 protease) and blocking proteolytic cleavage of protein precursors that are necessary for the production of infectious viral particles.

What makes an amino acid?

Proteins are all made of monomers—we knew that word would come in handy—called amino acids. There are 22 different kinds of naturally occurring amino acids, and each one is made of four components: - A central carbon with one hydrogen - One carboxyl group (-COOH) - One amino group (-NH2) - One R group (-R; Mr. Anonymous is back!) Carbon needs four bonds, which means that our central carbon needs an R group. Up until now, the R group has been rather anonymous, but it can be numerous things. In fact, the identity of the enigmatic R group is what gives each amino acid its identity. In the simplest case, the R group is a hydrogen (H), but the R group can sometimes be a chain of hydrocarbons, which are complex ringed structures. The R group can be polar, nonpolar, or even charged. Knowing what you know about polarity and charged particles, you can imagine how much these differences affect the properties of amino acids. R, you crazy wild card, you. Amino acids bind to each other by dehydration synthesis: the OH group on one amino acid's carboxyl group (-COOH) combines with one of the hydrogen groups from another amino acid's amino group (-NH2). We call the resulting covalent bond a peptide bond. When many amino acids bind together, it's called a polypeptide. To understand how proteins function, we need to understand how they're put together and what gives them their shape. Proteins actually have four levels of structure, each one more complex than the last. As you will soon learn, proteins can either be simple as pie or so high maintenance that you are ready to pull your hair out, which is made of protein by the way. Primary structure Secondary structure Tertiary structure Quaternary structure The first level, the primary structure, is a long string, or sequence, of amino acids linked together (aka a polypeptide chain). If we think of each amino acid as a letter in the alphabet, polypeptides would then be the words. The word "star" has four letters, and when we see this word, we think of a shiny speck in the night sky. Rearrange those letters and you can get "rats." Rats and stars are not at all the same thing even though the letters are, in fact, exactly the same. Now, we can modify that word further by replacing the letter R in "rat" with a B. Bats and rats are also not the same even if both are undesirable to have in your attic. The bottom line is that primary structures of proteins vary because the kinds of amino acids and/or the sequence of those amino acids vary. Secondary structure in proteins results from hydrogen bonds that form between parts of the polypeptide chain that are not variable. By not variable, we mean the parts that are not part of the infamous R group. These repeating, nonvariable parts include nitrogens that were originally part of amino groups, now called amides, and the remaining oxygens that are part of carboxyl groups. Both nitrogen and oxygen are somewhat bad at sharing electrons, so they create polar regions. The end result is that the polypeptide has several possible structures: the helix, the sheet, the coil, the loop, and the turn. While all of this bonding is going on, those R groups aren't just sitting there twiddling their imaginary thumbs and waiting for something to happen like they were a redshirt on Star Trek. They are interacting with other R groups, and these interactions give polypeptides their tertiary structure. See what we did there? In reality, the secondary and tertiary structures together give a protein it's three-dimensional (3D) shape. To use a food analogy (since we know how much you love those), a straight line of peas is a good way to think of a polypeptide chain with only primary structure, and a rotini noodle is a good way to think about a polypeptide once it has secondary and tertiary structure. Never mind the fact that both of those foods actually contain mostly carbohydrates. Some proteins join together in order to carry out their function. The quaternary structure is the overall shape that results once all the interacting subunits of the protein have clumped together. Collagen and hemoglobin are two good examples of proteins with quaternary structure. Read more about their function in our theme on structure and function.

it pushed the envelope

Pushing the envelope means testing limits and trying out new, often radical ideas.

why comets make dust tails?

Radiation from the sun pushes dust particles away from the coma, forming a dust tail, while charged particles from the sun convert some of the comet's gases into ions, forming an ion tail. Since comet tails are shaped by sunlight and the solar wind, they always point away from the sun.

Radio astronomy

Radio astronomers use different techniques to observe objects in the radio spectrum. Instruments may simply be pointed at an energetic radio source to analyze its emission. To "image" a region of the sky in more detail, multiple overlapping scans can be recorded and pieced together in a mosaic image. The type of instrument used depends on the strength of the signal and the amount of detail needed. Observations from the Earth's surface are limited to wavelengths that can pass through the atmosphere. At low frequencies, or long wavelengths, transmission is limited by the ionosphere, which reflects waves with frequencies less than its characteristic plasma frequency. Water vapor interferes with radio astronomy at higher frequencies, which has led to building radio observatories that conduct observations at millimeter wavelengths at very high and dry sites, in order to minimize the water vapor content in the line of sight. Finally, transmitting devices on earth may cause radio-frequency interference. Because of this, many radio observatories are built at remote places. Radio telescopes may need to be extremely large in order to receive signals with low signal-to-noise ratio. Also since angular resolution is a function of the diameter of the "objective" in proportion to the wavelength of the electromagnetic radiation being observed, radio telescopes have to be much larger in comparison to their optical counterparts. For example, a 1-meter diameter optical telescope is two million times bigger than the wavelength of light observed giving it a resolution of roughly 0.3 arc seconds, whereas a radio telescope "dish" many times that size may, depending on the wavelength observed, only be able to resolve an object the size of the full moon (30 minutes of arc).

Five-hundred-meter Aperture Spherical Telescope (FAST)

Radio telescope in China. It consists of a fixed 500 m (1,600 ft) diameter dish constructed in a natural depression in the landscape. It is the world's largest filled-aperture radio telescope. It has a novel design, using an active surface made of metal panels that can be tilted by a computer to help change the focus to different areas of the sky.[5] The cabin containing the feed antenna suspended on cables above the dish is also moved using a digitally-controlled winch by the computer control system to steer the instrument to receive from different directions. It observes at wavelengths of 10 cm to 4.3 m.

Relativistic beaming

Relativistic beaming (also known as Doppler beaming, Doppler boosting, or the headlight effect) is the process by which relativistic effects modify the apparent luminosity of emitting matter that is moving at speeds close to the speed of light. In an astronomical context, relativistic beaming commonly occurs in two oppositely-directed relativistic jets of plasma that originate from a central compact object that is accreting matter. Accreting compact objects and relativistic jets are invoked to explain the following observed phenomena: x-ray binaries, gamma-ray bursts, and, on a much larger scale, active galactic nuclei (AGN). (Quasars are also associated with an accreting compact object, but are thought to be merely a particular variety of AGN.) Relativistic jets emit most of their energy via synchrotron emission. In our simple model the sphere contains highly relativistic electrons and a steady magnetic field. Electrons inside the blob travel at speeds just a tiny fraction below the speed of light and are whipped around by the magnetic field. Each change in direction by an electron is accompanied by the release of energy in the form of a photon. With enough electrons and a powerful enough magnetic field the relativistic sphere can emit a huge number of photons, ranging from those at relatively weak radio frequencies to powerful X-ray photons.

Eukaryotic Ribosomes

Ribsomes are small cellular machines made of proteins and ribosomal RNA. All cells, both eukaryotic and prokaryotic, have ribosomes. Eukaryotic ribosomes are larger and have a slightly different shape and composition than those found in prokaryotic cells. Eukaryotic ribosomes, for instance, have about twice the amount of ribosomal RNA (rRNA) and one-third more ribosomal proteins (~83 vs. 53) than prokaryotic ribosomes have. Despite these differences, the function of the eukaryotic ribosome is virtually identical to the prokaryotic version. This is a remarkable example of what we call evolutionary unity. Ribosomes translate mRNA into protein, or the last step in the central dogma of biology described earlier. It all comes together.

Sexagesimal

Sexagesimal (also known as base 60 or sexagenary) is a numeral system with sixty as its base. It originated with the ancient Sumerians in the 3rd millennium BC, was passed down to the ancient Babylonians, and is still used—in a modified form—for measuring time, angles, and geographic coordinates.

Chrondrules

Small (usually about one millimeter in diameter), rounded, particles of silicate embedded in most stony meteorites.

List three similarities and three differences between plant and animal cells.

Some similarities are as follows: the presence of a nucleus, a cell membrane, ribosomes, DNA, RNA, proteins, mitochondria, cytoskeleton, cytoplasm, etc. Some differences are as follows: plant cells have chloroplasts, large vacuoles, and cell walls, while some animal cells have centrioles, flagella, and cilia.

How do plants protect their DNA from the sun? Do they ever get "skin" cancer?

Sometimes they do, like tree burls. Cancer isn't such an issue for plants as the mutated cells can't spread throughout the plant since they don't have anything like blood. As a result it is localised to an area and isn't really a problem. Edit: lots of people have pointed out sap runs through a tree, so perhaps this was a bit simplified. Plant cells tend to be quite different to animal cells, larger with thick cell walls and large vacuoles in the centre which makes them less free to flow around. However as some people have pointed out some tree cancers can spread to the sap and result in the trunk of a tree splitting and dying, although I don't believe this is common.

earliest known civilization

Sumer, located in Mesopotamia, is the first known complex civilization, developing the first city-states in the 4th millennium BCE. It was in these cities that the earliest known form of writing, cuneiform script, appeared around 3000 BCE. Cuneiform writing began as a system of pictographs.

Aztec Empire

The Aztec Empire flourished between c. 1345 and 1521 CE and, at its greatest extent, covered most of northern Mesoamerica The Aztecs were famous for their agriculture, cultivating all available land, introducing irrigation, draining swamps, and creating artificial islands in the lakes. They developed a form of hieroglyphic writing, a complex calendar system, and built famous pyramids and temples.

Burmese peacock softshell turtle

The Burmese Peacock Softshell is a very rare species of turtle which is endemic to Myanmar. The Burmese Peacock Softshell is within the superfamily of Trionychia which contains all softshell turtles and it diverged 144 million years ago, before the evolution of flowering plants.

How does the smooth endoplasmic reticulum (SER) differ from the rough endoplasmic reticulum (RER)?

The SER is the site of lipid production and is not studded with ribosomes. The RER is the site of protein production, especially membrane protein production, and is studded with ribosomes to make it rough and rowdy.

quorum sensing

The ability of bacteria to sense the presence of other bacteria via secreted chemical signals. In biology, quorum sensing is the ability to detect and to respond to cell population density by gene regulation. As one example, quorum sensing (QS) enables bacteria to restrict the expression of specific genes to the high cell densities at which the resulting phenotypes will be most beneficial. Many species of bacteria use quorum sensing to coordinate gene expression according to the density of their local population. In a similar fashion, some social insects use quorum sensing to determine where to nest. Also, quorum sensing might be useful for cancer cell communications too. In addition to its function in biological systems, quorum sensing has several useful applications for computing and robotics. In general, quorum sensing can function as a decision-making process in any decentralized system in which the components have: (a) a means of assessing the number of other components they interact with and (b) a standard response once a threshold number of components is detected.

Eukaryotic Cytoplasm and Cytoskeleton

The cytoplasm in eukaryotic cells is a gel-like, yet fluid, substance in which all of the other cellular components are suspended, including all of the organelles. The underlying structure and function of the cytoplasm, and of the cell itself, is largely determined by the cytoskeleton, a protein framework along which particles in the cell, including proteins, ribosomes, and organelles, move around. You can think of the cytoskeleton as a type of 3D "highway system" with roads running in every direction, including up and down. The cytoplasm is the thick fluid in which the "highway system" is suspended and through which cellular materials are transported. Helpful tip: whenever you see cyto- as part of a word, think "inside the cell." The central dogma is central to life, but there are exceptions! Reverse transcriptase is an enzyme found in viruses that can take RNA and make DNA. We know; we just blew your mind.

Prokaryotic Cytoplasm

The cytoplasm in prokaryotic cells is a gel-like, yet fluid, substance in which all of the other cellular components are suspended. Think Jell-O for cells. It is very similar to the eukaryotic cytoplasm, except that it does not contain organelles. Recently, biologists have discovered that prokaryotic cells have a complex and functional cytoskeleton similar to that seen in eukaryotic cells. The cytoskeleton helps a prokaryotic cell to divide and to maintain its plump, round shape. As is the case in eukaryotic cells, the cytoskeleton is the framework along which particles in the cell—including proteins, ribosomes, and small rings of DNA called plasmids—move around. It's the cell's "highway system" suspended in Jello.

What function does a double bilayer perform in mitochondria?

The double bilayer provides the spaces where protons can accumulate and flow through the inner mitochondrial membrane, or IMM. Without these spaces, the process of cellular respiration would cease altogether.

first city to have 1 million population

The first city known to man to reach a population of one million people was Rome, Italy in 133 B.C. London, England reached the mark in 1810 and New York City, USA made it in 1875. Regarding Beijing, China, it reached 1 million people in 1855.

Name the four main structures shared by all prokaryotic cells.

The four main structures shared by all prokaryotic cells are the plasma membrane, cytoplasm, ribosomes, and genetic material.

condensation astronomy

The growth of a particle by addition of material from surrounding gas atom by atom. Plays into accretion which is the sticking together of solid particles to produce a larger particle. The study of planet building is the study of these three processes: Condensation, Accretion, and Gravitational Collapse. Gravitational collapse is the process by which a forming body such as a planet gravitationally captures gas rapidly from the surrounding nebula. As the protoplanets formed heat accumulated in its interior both from the impacts of infalling planetesimals and from the decay of short-lived radioactive elements. This heat eventually melted the planet and allowed it to differentiate. Differentiation is the separation of material according to its density. Heavy metals fell to the core and light silicates went to the crust.

what element is most common on earth?

The most abundant element in the earth's crust is oxygen, making up 46.6% of the earth's mass. Silicon is the second most abundant element (27.7%), followed by aluminum (8.1%), iron (5.0%), calcium (3.6%), sodium (2.8%), potassium (2.6%). and magnesium (2.1%). These eight elements account for approximately 98.5% of the total mass of the earth's crust. Of course, the earth's crust is only the outer portion of the earth. Future research will tell us about the composition of the mantle and core. The most abundant elements in the upper mantle, and the mantle makes up 2/3 of the earth's mass, are olivine (Mg,Fe)2SiO4 and pyroxene (Mg,Fe)SiO3. At high pressure these collapse to dense cubic structures, and also form an oxide phase (Mg,Fe)O. These probably make up the lower mantle and are the most abundant minerals in the earth.

nucleus

The nucleus stores all the information a cell needs to grow, reproduce, and function. This information is contained in long but thin molecules of deoxyribonucleic acid, or DNA. One of the functions of the nucleus is to protect the cell's DNA from damage, but that is not all it does. The nucleus also contains a small, round body called a nucleolus, which is like DNA's apartment building. It's where the DNA and all of its attendant proteins hang out all day. The nuclear membrane has pores through which the contents of the nucleus communicate with the rest of the cell. The nuclear membrane tightly controls what gets into the nucleus and what gets out. This regulation of communication by the nuclear membrane has a great effect on what a cell looks like and what it does. Chromosomes are also located in the nucleus and are basically organized structures of DNA and proteins. In eukaryotes, the chromosomal DNA is packaged and organized into a condensed structure called chromatin. Chromosomes are single pieces of DNA along with genes, proteins, and nucleotides, while chromatin is a condensed package of chromosomes that basically allows all the necessary DNA to fit inside the nucleus. We will dive deeper into the world of chromosomes in another section, but for now, just remember that eukaryotic and prokaryotic cells each have genomes, the name for the entire set of an organism's genetic and hereditary information. Genomes are entirely encoded in either the DNA or the RNA. In the case of eukaryotes, multiple linear pieces of DNA comprise its genome. In eukaryotic organisms, the DNA inside the nucleus is also closely associated with large protein complexes called histones. Along with the nuclear membrane, histones help control which messages get sent from the DNA to the rest of the cell. The information stored in DNA gets transferred to the rest of the cell by a very elegant process—a process so common and so important to life that it is called the central dogma of biology. No, really. In eukaryotic cells, the first stage of this process takes place in the nucleus and consists of specific portions of the DNA, called genes, being copied, or transcribed, into small strands of ribonucleic acid, or RNA. RNA containing a copy, or transcript, of DNA is called messenger RNA, or mRNA. These mRNA molecules are then physically transported out of the nucleus through the pores (holes) in the nuclear membrane and into the cytoplasm, where they are eventually translated into proteins by ribosomes. Therefore, the central dogma of biology is simply: DNA → RNA → Protein And it all starts in the nucleus! (Warning: any discussion of the nucleus excludes prokaryotes. The nucleus is a eukaryotic song and dance number, and don't you forget it.) Most eukaryotic cells have a nucleus throughout their entire life cycles, but there are a few notable exceptions. Human red blood cells (the good ol' RBCs), for example, get rid of their nuclei as they mature. Rebels without a cause. Scratch that: rebels with a cause. With their nuclei removed, red blood cells have more space to carry oxygen throughout the body.

pin tumbler lock

The pin tumbler lock is a lock mechanism that uses pins of varying lengths to prevent the lock from opening without the correct key. Pin tumblers are most commonly employed in cylinder locks, but may also be found in tubular pin tumbler locks (also known as radial locks or ace locks). Above each key pin is a corresponding set of driver pins, which are spring-loaded. Simpler locks typically have only one driver pin for each key pin, but locks requiring multi-keyed entry, such as a group of locks having a master key, may have extra driver pins known as spacer pins. The outer casing has several vertical shafts, which hold the spring-loaded pins.

There are many photosynthetic plants, but have you heard of a photosynthetic animal? There is one that steals and uses the chloroplasts of the algae it consumes.

There are many photosynthetic plants, but have you heard of a photosynthetic animal? There is one that steals and uses the chloroplasts of the algae it consumes. Green Sea Slug Is Part Animal, Part Plant Shaped like a leaf itself, the slug Elysia chlorotica already has a reputation for kidnapping the photosynthesizing organelles and some genes from algae. Now it turns out that the slug has acquired enough stolen goods to make an entire plant chemical-making pathway work inside an animal body. The slugs can manufacture the most common form of chlorophyll, the green pigment in plants that captures energy from sunlight, Pierce reported January 7 at the annual meeting of the Society for Integrative and Comparative Biology. Pierce used a radioactive tracer to show that the slugs were making the pigment, called chlorophyll a, themselves and not simply relying on chlorophyll reserves stolen from the algae the slugs dine on. "This could be a fusion of a plant and an animal — that's just cool," said invertebrate zoologist John Zardus of The Citadel in Charleston, S.C. Microbes swap genes readily, but Zardus said he couldn't think of another natural example of genes flowing between multicellular kingdoms. Pierce emphasized that this green slug goes far beyond animals such as corals that host live-in microbes that share the bounties of their photosynthesis. Most of those hosts tuck in the partner cells whole in crevices or pockets among host cells. Pierce's slug, however, takes just parts of cells, the little green photosynthetic organelles called chloroplasts, from the algae it eats. The slug's highly branched gut network engulfs these stolen bits and holds them inside slug cells. Some related slugs also engulf chloroplasts but E. chlorotica alone preserves the organelles in working order for a whole slug lifetime of nearly a year. The slug readily sucks the innards out of algal filaments whenever they're available, but in good light, multiple meals aren't essential. Scientists have shown that once a young slug has slurped its first chloroplast meal from one of its few favored species of Vaucheria algae, the slug does not have to eat again for the rest of its life. All it has to do is sunbathe.

Chloroplasts

These organelles are responsible for converting the energy from the sun into chemical energy, usually in the form of glucose, through the elaborate process of photosynthesis. Chloroplasts are green because they contain large amounts of the green pigment chlorophyll bound to proteins embedded in internal stacks of membranes called thylakoids. Sunlight is captured by chlorophyll molecules and transferred throughout the thylakoid membranes to give off energy. This energy is used to strip carbon from carbon dioxide in the air to make sugar. Generally in any given plant, only some of the cells will contain chloroplasts. The chloroplast was also a free living bacterial cell once long ago, but its genome is much larger than that of a mitochondrion.

Barringer Crater

This crater is about 50,000 years old and is located in Arizona.

Nuclear Membranes

This membrane is found in only eukaryotic cells—because only eukaryotic cells have nuclei, right?—and is composed of a double bilayer. This means it has four total layers of phospholipids making up two distinct bilayers. The outer bilayer interacts with the cytoplasm and is physically connected to the rough endoplasmic reticulum (RER). In reality, you can think of the RER as an extension of the outer nuclear bilayer. This close membrane connectivity allows messenger RNA (mRNA) to move directly from the DNA in the nucleus to the ribosomes of the RER without ever coming in contact with the relatively harsh environment of the cytoplasm. The inner nuclear bilayer is studded with proteins that interact with the contents of the nucleus, especially DNA. Filaments called lamins connect the chromosomes to the inner membrane proteins and help the nucleus keep its shape. The space between the two bilayers is called the perinuclear space. Transcription factors, mRNA, and a few other little guys move across both bilayers and the perinuclear space through large channels called nuclear pores. The most fascinating aspect of these pores is that they can dilate and constrict to allow or block larger molecules' access across the nuclear membrane, much like the pupil in your eye gets larger or smaller to allow more or less light to reach the retina. Crazy stuff. Lastly, as the cell prepares for reproduction, proteins in the cytoplasm dissolve the nuclear membrane so that the duplicated DNA (something we will dive into a little later) can be separated to opposite sides of the cell. You read correctly; the nuclear membrane dissolves itself. After cell division, new nuclear membranes are formed in both of the "daughter" cells and resume their vital functions in protecting the DNA and providing communication between the nucleus and the rest of the cell. Nuclei of animal cells actually move around; they do this through cytoskeletal elements like microtubules and actin.

More on the Plasma Membrane

This structure keeps the contents of a cell separate from the environment surrounding it. In addition to phospholipids, the plasma membrane has cholesterol molecules and proteins that allow the membrane to function properly. Cholesterol molecules are primarily affect the rigidity of the plasma membrane. At lower temperatures, when the membrane would like nothing more than to freeze in place, cholesterol helps the membrane loosen up. At higher temperatures, though, cholesterol raises the melting point of the membrane, preventing it from smooshing into a mushy paste. Proteins embedded in the membrane play important roles in helping the cell transport materials in and out and communicate with its environment, including with other cells. There are two main types of membrane proteins: Those that transverse the membrane, called integral proteins Those that are stuck on the inside or outside of the membrane, called peripheral proteins Integral proteins are often involved in the transport of materials, while peripheral proteins generally function in cellular communication. All of these membrane components—lipids, cholesterol molecules, and proteins—can move laterally, or side-to-side, through the membrane, causing biologists to consider it as a kind of fluid. However, since the membrane is made up of a number of different components, it can also be considered a kind of mosaic. Yes, like a piece of art. These two ideas come together in what is known as the "Fluid-Mosaic Model" of the plasma membrane. Biologists have also recently learned that the plasma membrane and the cytoskeleton interact very closely with one another. Because the phospholipid bilayer is somewhat fluid, proteins embedded in the membrane could easily move around willy-nilly. To prevent this from happening, the cytoskeleton attaches to the membrane proteins and anchors them in place. Those guys aren't going anywhere. The interior of the phospholipid bilayer is hydrophobic, so only very small, neutrally charged molecules—such as oxygen (O2), carbon dioxide (CO2), and water (H2O)—can pass freely through the membrane. Everything else must pass through a transmembrane protein, meaning the cell has general control over what gets in and what gets out. The transmembrane protein can be thought of as the security guard at the door of the Sublime with Rome concert. He steals your plastic bottles and confiscates your food in the event that you get a little frisky and start chucking items at other concertgoers or, heaven forbid, at Rome because you still have pent-up aggression over Bradley's death, despite the fact that it was 15+ years ago. Poor Rome. Sorry, where were we again? In short, the plasma membrane plays the very same roles for a cell as your skin, eyes, ears, mouth, and nose play for your body. The phospholipids provide protection to the cell, while membrane proteins allow it to "eat," "drink," and "breathe," as well as "feel," "see," and "hear," the outside environment. Without the membrane proteins, a cell would lose all of its senses at once and would be as defenseless as a tree house in a tornado. We wouldn't want that, now would we? The plasma membrane is a very important part of the cell indeed. Your plasma membrane is the place where your cells meet all foreign material, including pathogens. Because of this fact, it's also the place where the cells of your immune system communicate with other cells.

Trehalose

Trehalose is a sugar consisting of two molecules of glucose. It is also known as mycose or tremalose. Some bacteria, fungi, plants and invertebrate animals synthesize it as a source of energy, and to survive freezing and lack of water. Organisms ranging from bacteria, yeast, fungi, insects, invertebrates, and lower and higher plants have enzymes that can make trehalose.[7] In nature, trehalose can be found in plants, and microorganisms. In animals, trehalose is prevalent in shrimp, and also in insects, including grasshoppers, locusts, butterflies, and bees, in which trehalose serves as blood-sugar. Trehalose is then broken down into glucose by the catabolic enzyme trehalase for use. Trehalose is the major carbohydrate energy storage molecule used by insects for flight. One possible reason for this is that the glycosidic linkage of trehalose, when acted upon by an insect trehalase, releases two molecules of glucose, which is required for the rapid energy requirements of flight. This is double the efficiency of glucose release from the storage polymer starch, for which cleavage of one glycosidic linkage releases only one glucose molecule. In plants, trehalose is seen in sunflower seeds, moonwort, Selaginella plants,[11] and sea algae. Within the fungi, it is prevalent in some mushrooms, such as shiitake (Lentinula edodes), oyster, king oyster, and golden needle.

Vesicles

Vesicles are small spheres of phospholipids made by the Golgi bodies and are responsible for transporting proteins, lipids, and steroids to various places throughout the cell, especially to the plasma membrane. The interior conditions of a vesicle are similar to the conditions of the surrounding cytosol, so transported proteins and lipids are not damaged en route to their destinations. Smart, those cells. Helpful tip: now that you know what lys- means, it will be easy to remember that lysosomes are made by Golgi bodies to break things up, and vesicles are made by Golgi bodies to move things around. Nice.

Membrane Transport

What you must understand if you want to comprehend membrane transport are the concepts of concentration gradients and diffusion. To start, let's look at an example you are likely to be familiar with. Imagine you are sitting in the corner of a stuffy room reading a snazzy lesson about cells on Shmoop. Now imagine that someone in the opposite corner of the room is getting ready for a big date, and he is spritzing on some cologne. Even if there are no air currents in the room, eventually you will be able to smell the cologne all the way in your corner. Ickfest. The reason you will be able to smell the spritz—try it out if you don't believe us—has to do with the concept of a concentration gradient. When the cologne is sprayed, the cologne molecules are highly concentrated on one side of the room. Without getting into all of the gory physics, the smelly molecules will immediately begin to disperse, or diffuse, into areas of the room where there is a lower, or zero, concentration of cologne. Eventually, the molecules will be diffused evenly throughout the room, all the way over into the opposite corner where you are sitting. The main idea is that molecules naturally move from areas of high concentration to low concentration. In other words, molecules move down their concentration gradient in the process of diffusion. Now, let's apply these concepts of concentration gradients and diffusion to the membranes of cells. Recall that big molecules and charged ions cannot simply cross the plasma membrane, even though some small molecules and noncharged ions can cross freely. The membrane feature of allowing some things to cross while keeping others out is called semi-permeability. All membranes are semipermeable. Molecules that freely cross cell membranes do so through the process of simple diffusion. That is, they move from a high concentration outside the cell to a lower concentration inside the cell, or vice versa. Carbon dioxide (CO2) and oxygen (O2) are both molecules that can move across cell membranes through simple diffusion. When you breathe in oxygen, the red blood cells in your lungs have a low concentration of oxygen and a high concentration of carbon dioxide inside. When the fresh oxygen molecules in your lungs come into contact with your red blood cells, they diffuse rapidly across your red blood cell membranes into the cells, or down their concentration gradient. At the same time, carbon dioxide molecules diffuse rapidly out of the red blood cells, down their concentration gradient, and into your lungs. When water molecules move freely across a cell membrane, the process is called osmosis, which is just a special type of simple diffusion. The diffusion is so simple that it'd be like balancing a biology book on your head and instantly learning all of the material. You can see where that would be handy, right? Osmosis is incredibly important to sustaining life. We generally consider water as a solvent, or the medium in which other things are dissolved (there we go again with the use of sol-). So understanding which direction water will move across a cell membrane in a given situation can be a bit tricky. To help you out, we have devised a short exercise you can work through as you consider a situation involving osmosis across a cell membrane. You can thank us later. First, what are the solutes? That is, what are the things dissolved in the water? Second, can these solutes move freely across the cell membrane? If solute molecules cannot move freely across the membrane, is there a higher concentration of solutes inside the cell than outside? If so, then water will move via osmosis into the cell, so the concentration of solutes is equal on both sides of the membrane. Keep in mind that you can decrease concentration bydecreasing the number of solute molecules in a given area.increasing the number of solvent molecules, usually water, in a given area. Because the solutes cannot move across the membrane, the water molecules must. If not, then water will move via osmosis out of the cell, so the concentration of solutes is equal on both sides of the membrane.If solute molecules can move freely across the cell membrane, the movement of water by osmosis is not as important, because the solute molecules themselves will diffuse across the membrane to create an equal concentration on both sides. Why should you care about osmosis? One relevant example should convince you that the process is essential to keeping you alive. Let's look at red blood cells again. These important cells are suspended in a fluid called blood plasma. Blood plasma is composed of water and solutes, including salts. The cytoplasm of your red blood cells is also composed of water and solutes, including salts. By the way, salts are solutes that cannot freely cross the cell membrane. Let's say the concentration of salts in the plasma is higher than the concentration of salts in your red blood cells. Using the exercise above, predict which direction the water molecules will move. We'll give you a moment. Time's up! If you predicted correctly, you said that water molecules would move out of the red blood cells and into the blood plasma by osmosis. When this occurs, red blood cells shrivel up and become unable to carry oxygen or carbon dioxide. Definitely not good. Now let's say that the concentration of salts is higher in the cytoplasm than in the blood plasma. Which direction will water molecules move? We'll give you another moment (this time without the theme music). If you predicted correctly, you said that water molecules would move from the blood plasma into the red blood cells by way of osmosis. The result? The red blood cells would swell and eventually burst, or lyse. Again, this does not sound like too much fun. Since our red blood cells, under normal conditions, are not shriveled and do not regularly burst, what does this say about the concentration of solutes, especially salts, in the blood plasma compared to the concentration of solutes in the cytoplasm of our red blood cells? If you are starting to grasp the concepts of diffusion, concentration gradients, and osmosis, you would say that the concentration of salts in the plasma is equal to the concentration of salts in the cytoplasm of red blood cells (again, under normal conditions). This statement is correct. With this background in osmosis, you are ready to tackle one of the more confusing concepts regarding movement of materials across cell membranes: the concept of tonicity. Simply put, tonicity is a term that describes the concentration of solutes on both sides of a cell membrane. Because it describes two concentrations, whenever you describe the tonicity of a solution on one side of a cell membrane—like, say, the tonicity of the cytoplasm of a red blood cell—you are also describing the tonicity of the solution on the other side—the tonicity of the blood plasma. To describe the tonicity of solutions, we add a prefix to the word "tonic" to say whether the concentration of solutes on one side of a membrane is high, low, or equal to the concentration of solutes on the other side. These prefixes are: Hyper- (high) Hypo- (low) Iso- (equal) To solidify this concept, let's look at the red blood cell example again. In the first situation, we said that the concentration of solutes, or salts, in the cytoplasm of the red blood cells was lower than the concentration of solutes in the blood plasma. In terms of tonicity, we could simply say the cytoplasm of the red blood cells was hypotonic to the blood plasma. Much tidier, right? Under normal conditions, when red blood cells are not shriveled or bursting, what is the tonicity of the red blood cell cytoplasm relative to the blood plasma? Yep, isotonic. But what about the molecules that are so freakin' big and/or charged that they cannot simply diffuse across cell membranes? How do they get into and out of cells and organelles? In situations where simple diffusion across the membrane is not possible, membrane channel proteins play an important role. When the concentration of big molecules is higher outside the cell than inside, and if the right proteins exist in the membrane, these big molecules can move down their concentration gradient through channel proteins into the cell. This process of diffusion through a membrane protein is called facilitated diffusion, and it can occur in either direction, into or out of a cell, depending on where the concentration of molecules is higher. In addition to facilitated diffusion, cells are able to move big and/or charged molecules through membrane proteins against, or up, the molecules' concentration gradients. Impressive. Because doing this goes against the natural flow of molecules down their concentration gradients, cells must put energy into the process, generally in the form of ATP. Who knew ATP was so darn useful? For this reason, the movement of molecules up their concentration gradient is called active transport. One example of active transport you should now be familiar with occurs in the mitochondria, where protons (hydrogen ions, H+) are actively pumped against their concentration gradient from the matrix into the intermembrane space. On the other hand, the movement of molecules down their concentration gradient across a membrane is called passive transport. To recap, types ofpassive transport include: Diffusion Osmosis Facilitated diffusion The movement of protons from the intermembrane space back into the matrix through ATP synthase is an example of passive transport. However, this type of passive transport is coupled, or connected, to the active transport that occurred just before this to pump protons into the intermembrane space. In fact, the whole purpose of pumping protons into the intermembrane space in the first place is to create a concentration gradient down which protons can flow back into the matrix through ATP synthase to make ATP. In the end, it is clear that the transport of materials across cell membranes is a critically important function of those membranes. Without such transport, cells and the organisms they comprise would quickly die. And we would not want that, seeing as we are part of that group of organisms. Cystic fibrosis is a genetic disease that is fundamentally about a disorder in membrane transport. The protein affected is called the Cystic Fibrosis Transmembrane Conductance Regulator.

Is cellular respiration a type of cell "breathing"?

When we talk about cellular respiration, we are not talking about a cell exchanging gases with its environment. Cellular respiration is a term that refers to the process by which glucose and other large carbon-based molecules are converted into ATP in the mitochondria. Be careful not to confuse whole-organism respiration, or breathing, with cellular respiration, which is basically ATP production.

Widmanstätten pattern

Widmanstätten patterns, also known as Thomson structures, are figures of long nickel-iron crystals, found in the octahedrite iron meteorites and some pallasites. They consist of a fine interleaving of kamacite and taenite bands or ribbons called lamellae. The Widmanstätten structures form due to the growth of new phases within the grain boundaries of the parent metals, generally increasing the hardness and brittleness of the metal. The structures form due to the precipitation of a single crystal-phase into two separate phases. Caused by a material cooling very slowly from a molten state and having been inside a fairly large object.

Window tax

Window tax was a property tax based on the number of windows in a house. It was a significant social, cultural, and architectural force in England, France, Ireland and Scotland during the 18th and 19th centuries. To avoid the tax some houses from the period can be seen to have bricked-up window-spaces (ready to be glazed or reglazed at a later date). In England and Wales it was introduced in 1696 and was repealed in 1851, 155 years after first being introduced. France (established 1798, repealed 1926) and Scotland both had window taxes for similar reasons. The reason it was implemented is that they thought rich people would have more windows. What ended up happening is that everyone closed up their windows because screw taxes.

Yayoi culture

Yayoi culture, (c. 300 BCE-c. 250 CE), prehistoric culture of Japan, subsequent to the Jōmon culture. Named after the district in Tokyo where its artifacts were first found in 1884, the culture arose on the southern Japanese island of Kyushu and spread northeastward toward the Kantō Plain. The Yayoi people mastered bronze and iron casting. They wove hemp and lived in village communities of thatched-roofed, raised-floor houses. They employed a method of wet paddy rice cultivation, of Chinese origin, and continued the hunting and shell-gathering economy of the Jōmon culture.

Do any human cells have flagella? If so, which ones?

Yes. Human sperm cells have flagella.

Do organisms like bacteria or tardigrades sleep? Or something equivalent to sleep?

Yes. Plants, too, will stop photosynthesis after eight to twelve hours depending on species and latitude, and instead their metabolism switches to the same as animals have: Use O2, produce CO2. Bacteria can become periodically dormant; during that time they don't undergo cell division and their metabolism slows. However it is important to note that particularly for Bacteria that make spores, this is a direct survival strategy because in that state, they are more likely to survive any adverse conditions. I don't know anything particular about tardigrade sleep but Caenorhabditis elegans - a thread worm that is extremely popular in biological research - does sleep, too. It has slightly over 40 300 neurons in total and we know what every single one does, but it also periodically reduces its overall activity and rests - sleep for all intents and purposes. Perchance to dream? Who knows.

How is it possible to have high voltage and low current? It seems to contradict the relationship between current and voltage in E=IR

You're confusing "high voltage" with "high voltage loss". Ohm's Law governs the loss of voltage across a resistance for a given current passing through it. Since the current is low, the voltage loss is correspondingly low. Relating to high voltage power transmission lines.

Iridium anomaly

Yucatan Meteor linked to high amounts of iridium in clay. Iridium is found in meteorites in much higher abundance than in the Earth's crust The term iridium anomaly commonly refers to an unusual abundance of the chemical element iridium in a layer of rock strata at the Cretaceous-Paleogene (K-Pg) boundary. The unusually high concentration of a rare metal like iridium is often taken as evidence for an extraterrestrial impact event. Iridium is a very rare element in the Earth's crust, but is found in anomalously high concentrations (around 100 times greater than normal) in a thin worldwide layer of clay marking the boundary between the Cretaceous and Paleogene periods, 66 million years ago. This boundary is marked by a major extinction event, including that of the dinosaurs along with about 70% of all other species. The clay layer also contains small grains of shocked quartz and, in some places, small weathered glass beads thought to be tektites.[1] A team consisting of the physicist Luis Alvarez, his son, geologist Walter Alvarez, and chemists Frank Asaro and Helen Vaughn Michel were the first to link the extinction to an extraterrestrial impact event based on the observation that iridium is much more abundant in meteorites than it is on Earth.[2] This theory was later substantiated by other evidence, including the eventual discovery of the impact crater, known as Chicxulub, on the Yucatan Peninsula in Mexico.

buzzard

a large predatory bird, similar to a vulture, that feeds mainly on carrion a large hawklike bird of prey with broad wings and a rounded tail, typically seen soaring in wide circles.

harpy

a predatory person or nagging woman A harpy is a mean, foul-tempered woman. You might quietly refer to your cranky math teacher as a harpy.

tweed

a rough-surfaced woolen cloth, typically of mixed flecked colors, originally produced in Scotland.

Planetesimal

a small body from which a planet originated in the early stages of development of the solar system (solar nebula) eventually forming protoplanets. Comets and asteroids are remnants of planetesimals

Cinder

a small piece of partly burned coal or wood that has stopped giving off flames but still has combustible matter in it.

bezoar

a small stony concretion that may form in the stomachs of certain animals, especially ruminants, and which was once used as an antidote for various ailments. image is of a trichobezoar Trichobezoars is composed of patient's own hair and is rare in children. The condition is usually associated with mentally retarded children and may be caused by a variety of conditions, including anxiety, depression, and family stress.

Mudflat

a stretch of muddy land left uncovered at low tide.

grifter

a swindler, dishonest gambler, or the like A grifter is a con artist: someone who swindles people out of money through fraud.

Carbonaceous chondrite

a type of meteorite containing many tiny glass spheres (chondrules) of rocky or metallic material stuck together by carbon-rich material Carbonaceous chondrites are primitive and undifferentiated meteorites that formed in oxygen-rich regions of the early solar system so that most of the metal is not found in its free form but as silicates, oxides, or sulfides.

misdirection

a wrong direction, guidance, or instruction to hide something else. Hiding the truth; a wrong instruction

when did flowering plants first appear?

about 125 million years ago Angiosperms ("seed in a vessel") produce a flower containing male and/or female reproductive structures. Fossil evidence indicates that flowering plants first appeared in the Lower Cretaceous, about 125 million years ago, and were rapidly diversifying by the Middle Cretaceous, about 100 million years ago.

glade

an open space in a forest a tract of land with few or no trees in the middle of a wooded area

two major kinds of prokaryotes

bacteria and archea As you may have read earlier in this unit, biologists now estimate that each human being carries nearly 20 times more bacterial, or prokaryotic, cells in his or her body than human, or eukaryotic, cells. If that statistic overwhelms you, rest assured that most of these bacteria are trying to help you, not hurt you. There are four main structures shared by all prokaryotic cells, bacterial or archaean: The plasma membrane Cytoplasm Ribosomes Genetic material (DNA and RNA) Some prokaryotic cells also have other structures like the cell wall, pili (singular "pillus"), and flagella (singular "flagellum"). Each of these structures and cellular components plays a critical role in the growth, survival, and reproduction of prokaryotic cells.

exploits

brilliant or heroic acts or deeds; adventures a software tool designed to take advantage of a flaw in a computer system, typically for malicious purposes such as installing malware.

how does an enzyme speed up a reaction?

by lowering the activation energy Catalysts lower the activation energy for reactions. The lower the activation energy for a reaction, the faster the rate. Thus enzymes speed up reactions by lowering activation energy. Many enzymes change shape when substrates bind. Enzymes are like the fast-forward button on your DVR remote. They buzz about 24/7 and involve themselves in chemical reactions, yet they always have these two properties: - They don't change the thermodynamic properties of the reaction. - They aren't consumed or modified in the reaction. We can study enzymes in the context of activation energy. Many biochemical reactions need a little input of energy to jump-start a thermodynamically favorable reaction. The activation energy is the amount of energy needed for the reaction to go forward and get over its activation barrier. ATP (adenosine triphosphate), the cell's energy molecule, needs a little help to get over its activation barrier. Otherwise, ATP might donate its terminal (read: end) phosphate group prematurely, resulting in an untimely release of energy. That would be bad—very bad. The cell makes sure that a reaction occurs when and where it wants by controlling the availability and abundance of enzymes. The need to reach the activation energy can be compared to when a roller coaster needs to be "pulled" up the track and to the top of the hill before it can go rolling down at exhilarating speeds. Until the coaster makes it over the hump, it won't be able to proceed down the other side. It's helpful to look at chemical reactions using an energy diagram (see below). Enzymes lower the activation energy of desired reactions and kick-start them to get those reactions rolling. Enzymes are usually extremely specific, meaning that one enzyme only catalyzes one type of biochemical reaction. How is the specificity of an enzyme determined? Their pickiness comes from the enzyme's active site, a unique binding site that only a particular substrate will recognize and be able to fit inside. The active site isn't changed after an enzyme catalyzes a reaction, so a new substrate can still fit in the site when the old substrate has gone away. Because enzymes are proteins, they can be a bit fragile. Like all proteins, an enzyme is only as good as its structure. Things like temperature, pH, or salt content can take a properly folded enzyme and turn it into garbage. A protein that isn't neatly folded can't do its job. This is called denaturation, and it spells disaster for any enzyme. At high temperatures, for example, the shape of an enzyme can change, and if that happens, it's likely that the active site will look different. The substrate won't fit into the new site, meaning the enzyme is pretty much useless. Ever wonder why apple slices turn brown? Apples brown because of a family of enzymes called PPO (polyphenol oxidase, if you must know). These enzymes catalyze a reaction between the oxygen in the air and the iron-containing compounds in apples. The result? Enzymatic browning.

Elam

conflicted with Mesopotamia but also had close cultural ties; stole treasure from Mesopotamia to Susa (their capital) Proto-Elamite civilization grew up east of the Tigris and Euphrates alluvial plains; it was a combination of the lowlands and the immediate highland areas to the north and east. At least three proto-Elamite states merged to form Elam Elam was an long-lasting ancient civilization just to the east of Mesopotamia, in what is now southwest Iran. Elam was centered in the far west and southwest of what is now modern-day Iran, stretching from the lowlands of what is now Khuzestan and Ilam Province as well as a small part of southern Iraq.. 2700 - 539 BC

one-off

done, made, or happening only once and not repeated.

hyperkinetic

frenetic; hyperactive uncontrolled bodily movement; spasm

Reduction (Chemistry)

gain electrons Reduction is a chemical reaction that involves the gaining of electrons by one of the atoms involved in the reaction between two chemicals. The term refers to the element that accepts electrons, as the oxidation state of the element that gains electrons is lowered.

Lakes of Titan

he lakes of Titan, Saturn's largest moon, are bodies of liquid ethane and methane that have been detected by the Cassini-Huygens space probe, and had been suspected long before.[2] The large ones are known as maria (seas) and the small ones as lacūs (lakes). During a Cassini flyby in late February 2007, radar and camera observations revealed several large features in the north polar region interpreted as large expanses of liquid methane and/or ethane, including one, Ligeia Mare, with an area of 126,000 km^2 (48,649 sq. mi.) ( (slightly larger than Lake Michigan-Huron, the largest freshwater lake on Earth), and another, Kraken Mare, that would later prove to be three times that size. A flyby of Titan's southern polar regions in October 2007 revealed similar, though far smaller, lakelike features. Radar measurements made in July 2009 and January 2010 indicate that Ontario Lacus is extremely shallow, with an average depth of 0.4-3.2 m (1'4"-10.5'), and a maximum depth of 2.9-7.4 m (9.5'-24'4").[16] It may thus resemble a terrestrial mudflat. In contrast, the northern hemisphere's Ligeia Mare has depths of 170 m (557'9"). The exact blend of hydrocarbons in the lakes is unknown. According to a computer model, 3/4 of an average polar lake is ethane, with 10 percent methane, 7 percent propane and smaller amounts of hydrogen cyanide, butane, nitrogen and argon.[21] Benzene is expected to fall like snow and quickly dissolve into the lakes, although the lakes may become saturated just as the Dead Sea on Earth is packed with salt. The excess benzene would then build up in a mud-like sludge on the shores and on the lake floors before eventually being eroded by ethane rain, forming a complex cave-riddled landscape.[22] Salt-like compounds composed of ammonia and acetylene are also predicted to form. No waves were initially detected by Cassini as the northern lakes emerged from winter darkness (calculations indicate wind speeds of less than 1 meter per second (2.2 MPH) should whip up detectable waves in Titan's ethane lakes but none were observed). This may be either due to low seasonal winds or solidification of hydrocarbons. Cyclones driven by evaporation and involving rain as well as gale-force winds of up to 20 meters per second (72 km/h [45 MPH]) are expected to form over the large northern seas only (Kraken Mare, Ligeia Mare, Punga Mare) in northern summer during 2017, lasting up to ten days.

ferritin

iron storage protein found in the liver, spleen, and red bone marrow Ferritin is a universal intracellular protein that stores iron and releases it in a controlled fashion. The protein is produced by almost all living organisms, including archaea, bacteria, algae, higher plants, and animals. In humans, it acts as a buffer against iron deficiency and iron overload.

tDCS (transcranial direct current stimulation)

is a form of neurostimulation which uses constant, low current delivered to the brain area of interest via electrodes on the scalp. It was originally developed to help patients with brain injuries such as strokes Essentially nudges neurons and increases their chance of firing. Lowers the action potential, maybe?

potassium-40 dating

is a radiometric dating method used in geochronology and archaeology. It is based on measurement of the product of the radioactive decay of an isotope of potassium (K) into argon (Ar). Can also use Ca and Ar for dating purposes. Potassium-40 is a rare example of an isotope that undergoes both types of beta decay. In about 89.28% of events, it decays to calcium-40 (40Ca) with emission of a beta particle (β−, an electron) with a maximum energy of 1.31 MeV and an antineutrino. In about 10.72% of events, it decays to argon-40 (40Ar) by electron capture (EC), with the emission of a neutrino and then a 1.460 MeV gamma ray.

Phoenicians

located on eastern Mediterranean coast; invented the alphabet which used sounds rather than symbols like cuneiform Phoenicia was an ancient civilization in Canaan which covered most of the western, coastal part of the fertile Crescent. Several major Phoenician cities were built on the coastline of the Mediterranean. It was an enterprising maritime trading culture that spread across the Mediterranean from 1550 BCE to 300 BCE. Probably the ancestor of the Western phonetic alphabet. Purple as the color of royalty (1) Navigation by the stars (Possibly circumnavigating Africa) Keels in the middle of a ship's hull for stability. Coating ship planks with bitumen tar for waterproofing

oxidation

loss of electrons

meso-

middle, mid

self-deprecating

modest about or critical of oneself, especially humorously so belittling or undervaluing oneself; excessively modest

Bipolar flows

narrow columns of high-speed gas ejected by a protostar in two opposite directions Bipolar flows are a phenomenon associated with young stars still embedded in their parent molecular clouds. There are two kinds of flows - jets and molecular outflows. The first represent high-speed stellar wind gas, ejected into two narrow streams. The second are broader cones of more slowly moving cloud gas.

He was never going to let me live it down.

never let you forget something

Eukaryotic Plasma Membrane

phospholipid bilayer with proteins and cholesterol embedded in it Phospholipids line up next to each other because part of the molecule is attracted to water (the "phospho" part), and the other part is repelled by water (the "lipid" part). Because the lipid part is repelled by water, it cannot be left out in the open, so another layer of phosopholipids will line up next to the first layer, with the "lipid" parts facing each other at the line where the two layers meet. At the same time, the "phospho" parts face outward toward the water on both sides of the line. As more and more "lines" of phospholipids are added adjacently to the first line, but in the same plane, a phospholipid bilayer is born! All prokaryotic cells have a phospholipid bilayer, or sometimes multiple bilayers, called the plasma membrane. This structure marks the boundary between the inside and outside of the cell, even though it is found on the inside of the prokaryotic cell wall. The cytoplasm and other prokaryotic cellular contents are found inside the plasma membrane. All eukaryotic cells have a plasma membrane, too. They also sport additional phospholipid membranes surrounding internal structures like the nucleus, the mitochondria, and the chloroplasts. Each of these internal membranes plays a vital and unique role in the growth, survival, and development of the cell.

Dinoflagellates

plant-like protist that causes red tide Group of protists that form "blooms", can be toxic. make up phytoplankton and can be bioluminescent. They generally have two flagella, half are heterotrophic and the other half are photosynthetic, many species are luminescent The dinoflagellates are protists constituting the phylum Dinoflagellata. Usually considered algae, dinoflagellates are mostly marine plankton, but they also are common in freshwater habitats. Their populations are distributed depending on sea surface temperature, salinity, or depth

reacquaint

refamiliarize To reacquaint is to get to know someone again, or to become familiar with something once more. If you move back to Boston after several years in Tokyo, you might have to reacquaint yourself with the subway system.

commiserating

showing sorrow or pity for express or feel sympathy or pity; sympathize

oology

study of eggs the branch of zoology that studies eggs (especially birds' eggs and their size, shape, coloration, and number)

inlay

substance embedded in another, contrasting material decorate the surface of by inserting wood, stone, and metal

paranoic

suffering from or relating to paranoia. showing unjustified suspicion and mistrust of other people.

c'est la vie

that's life, such is life

pedagogy

the art of teaching the method and practice of teaching, especially as an academic subject or theoretical concept.

proteolysis

the breakdown of proteins or peptides into amino acids by the action of enzymes (protease)

uncompressed density

the density a planet would have if its gravity did not compress it The uncompressed density of a terrestrial planet is the average density its materials would have at zero pressure. A greater uncompressed density indicates greater metal content.

Signal-to-noise ratio (SNR)

the level of a signal relative to a background of noise Signal-to-noise ratio (abbreviated SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in decibels. A ratio higher than 1:1 (greater than 0 dB) indicates more signal than noise.

outgassing

the release of gases from a planet's interior If planets formed and were later melted by radioactive decay, gases released from the planets interior would form an atmosphere.

Condensation sequence

the sequence in which different materials condense from the solar nebula at increasing distances from the sun

the jury is still out on ___________

used when you are saying that something is still not certain a decision has not yet been reached on a controversial subject.

Radio galaxy

very bright, often giant, elliptical galaxy that emits as much or more energy in the form of radio wavelengths as it does wavelengths of visible light The radio emission from radio-loud active galaxies is synchrotron emission, as inferred from its very smooth, broad-band nature and strong polarization. This implies that the radio-emitting plasma contains, at least, electrons with relativistic speeds (Lorentz factors of ~10^4) and magnetic fields. Since the plasma must be neutral, it must also contain either protons or positrons. There is no way of determining the particle content directly from observations of synchrotron radiation. Moreover, there is no way to determine the energy densities in particles and magnetic fields from observation: the same synchrotron emissivity may be a result of a few electrons and a strong field, or a weak field and many electrons, or something in between. It is possible to determine a minimum energy condition which is the minimum energy density that a region with a given emissivity can have, but for many years there was no particular reason to believe that the true energies were anywhere near the minimum energies.[2]