exam 3
Food Calories: Calories are units of energy:
(cal) is the amount of energy that can raise the temperature of 1 gram (g) of water by 1 degree celcius.
With enzyme
an enzyme speeds the chemical reaction by lowering the activation energy barrier.
when does entropy increase?
every time energy is converted from one form to another entropy increases.
conservation of energy principle
explains that it is not possible to destroy or create energy. energy can only be converted from one form to another.
Passive transport of one type of molecule
The membrane is permeable to these dye molecules, which diffuse down the concentration gradient. At equilibrium, the molecules are still restless, but the rate of transport is equal in both directions.
What is chemical energy?
The molecules of food, gasoline, and other fuels have a form of potential energy called chemical energy: arises from the arrangement of atoms and can be released by a chemical reaction.
how does the electron transport drive atp synthase?
The proton gradient produced by proton pumping during the electron transport chain is used to synthesize ATP. Protons flow down their concentration gradient into the matrix through the membrane protein ATP synthase, causing it to spin (like a water wheel) and catalyze conversion of ADP to ATP
Active Transport example
The transport protein (purple) has a binding site that accepts only a certain solute. Using energy from ATP, the protein pumps the solute against its concentration gradient.
Enzyme Activity Example
1. With its active site empty, lactase can accept a molecule of its substrate. (substrate -lactose-) 2. Substrate binds to the enzyme at the active site. (->h2o) 3. the enzyme catalyzes the chemical reaction, converting substrate to product. 4. the products are released, and lactase can accept another molecule of substrate.
calvin cycle 3
1. an enzyme adds each co2 to a five-carbon sugar called RuBP. The resulting molecule breaks into two three-carbon molecules. 2. using energy from atp and nadph produced by the light reactions, enzymes convert each three-carbon molecule to the three-carbon sugar G3P. 3. For every three molecules of co2 that enter the cycle, the net output is one g3p sugars continue in the cycle. 4. using energy from atp, enzymes rearrange the remaining g3p sugars to regenerate RuBP.
energy conversions during a dive
1. on the platform the diver has more potential energy 2. Diving connects potential energy to kinetic energy 3. In the water, the diver has less potential energy 4. Climbing the steps converts kinetic energy of muscle movement to potential energy.
ATP drives several cellular processes:
1. the production of a cell's large molecules from smaller molecular building blocks (anabolism), 2. muscle cell contraction for movement, 3. enables the transport of ions in nerve cells.
ATP yield during Cellular Respiration
32 atp
photosynthesis formula
6CO2 + 6H2O + sunlight ---> C6 H12 O6 + 6O2
Enzymes
A living organism contains a vast collection of chemicals and countless chemical reactions constantly change the organism's molecular makeup. The total of all the chemical reactions is an organism is called metabolism. Most metabolic reactions occur with the help of enzymes: -proteins that speed up chemical reactions without being consumed by those reactions. All living cells contain thousands of different enzymes, each promoting a different chemical reaction.
conservations of energy: power plant example
A power plant, for example, does not make energy; it merely converts it from one form (energy stored in coal) to a more convenient form (such as electricity).
Without enzyme
A reactant molecule must overcome the activation energy barrier before a chemical reaction can break the molecule into products
Enzyme 3
After the products are released from the active site, the enzyme can accept another molecule of substrate In fact, the ability to function repeatedly is a key characteristic of enzymes Like lactase, many enzymes are named for their substrates, with an -ase ending
what happens when heat is released?
Although releasing heat does not destroy energy, it does make it more difficult to harness for useful work
Enzyme Activity
An enzyme is very selective in the reaction it catalyzes. this selectivity is based on the enzyme's ability to recognize a certain reactant molecule, which is called the enzyme's substrate. A region of the enzyme called the active site has a shape and chemistry that fits the substrate molecule. The active site is typically a pocket or groove on the surface of the enzyme.
cellular respiration formula
C6H12O2 + 6O2 ------> 6CO2 + 6H20 + Energy (ATP)
What is rich in chemical energy?
Carbohydrates, fats, and even gasoline have structures that make them especially rich in chemical energy.
The ATP Cycle
Cells spend ATP continuously. Fortunately, it is a renewable resource. ATP can be restored by adding a phosphate group back to ADP. The chemical energy that cellular respiration harvests from sugars and other organic fuels is put to work regenerating a cell's supply of ATP. Cellular work spends ATP, which is recycled when ADP and phosphate are combined using energy released by cellular respiration. Thus, energy from processes that yield energy is transferred to processes that consume energy, such as muscle contraction.
How do enzymes enable metabolism to occur?
Enzymes enable metabolism to occur by reducing the amount of activation energy required to break the bonds of reactant molecules. It does so by binding to reactant molecules and putting them under physical or chemical stress, making it easier to break their bonds and start a reaction.
ATP power
For ATP power, it is release of the phosphate at the tip of the triphosphate tail that makes energy available to working cells. What remains is ADP, adenosine diphosphate (two phosphate groups, instead of three).
Activation Energy
For a chemical reaction to begin, chemical bonds in the reactant molecules must be broken. This process requires that the molecules absorb energy from their surroundings. For most chemical reactions, a cell has to spend a little energy to make more. The energy that must be invested to start a reaction is called activation energy because it activated the reactants and trigger the chemical reaction.
Energy Conversions in a car
Fuel rich in chemical energy: Octane (from gasoline) + oxygen. Combustion goes through the car, heat energy comes off the car, kinetic energy of movement leaves the car. Waste products in chemical energy: carbon dioxide+water
Energy conversion in a cell: energy conversions in a cell
Glucose+ Oxygen: Cellular Respiration goes through, heat energy and atp come out. Waster products poor in chemical energy: carbon dioxide+water
what is heat?
Heat is energy in its most disordered, chaotic form; the energy of aimless molecular movement.
Food Calories
In living organisms, of course, food is not used to boil water but instead used to fuel the activities of life.
Cellular Transport
It is the movement of substances across the cel membrane either into our out of the cell. Sometimes things just move through the phospholipid bilayer. Other times, substances need the assistance of a protein to cross the cell membrane.
how photosystems harvest light energy 2
Most pigments release heat energy as their light-excited electrons fall back to their ground state: that's why a surface with a lot of pigment, such as a black driveway, gets so hot on a sunny day But some pigments emit light as well as heat after absorbing photons
The Structure of ATP:
The abbreviation of ATP stands for adenosine triphosphate. ATP consists of an organic molecule called adenosine plus a tail of three phosphate groups. The triphosphate tail is the "business" end of ATP, the part that provides energy for cellular work. Each phosphate group is negatively charged. Negative repel each other. The crowding of negative charges in the triphosphate tail contributes to the potential energy of ATP.
Plant turgor
Turgor is necessary for plants to retain their upright posture and the extended state of their leaves. Watering a wilted plant will make it regain its turgor.
Phosphate Transfer
When ATP drives work in cells by being converted to ADP, the released phosphate groups do just fly off into space. ATP energizes other molecules in cells by transferring phosphate groups to those molecules. When a target molecule accepts the third phosphate group, it becomes energized and can then perform work in the cell.
entropy
a measure of the amount of disorder, or randomness, in a system
Heat
a type of kinetic energy contained in the random motion of atoms and molecules.
what do all energy conversions generate
all energy conversions generate some heat.
solutions
animal cells: isotonic=normal, hypotonic=lysing/explode, hypertonic solution= shriveled plant cells: isotonic=flaccid(wilts), hypertonic solution= turgid(normal), hypertonic=shriveled
conservation of energy: what is the chemical energy of food converted to?
chemical energy from food is converted to kinetic energy, the energy of motion.
why are leaves green?
chlorophyll and other pigments in chloroplasts reflect or transmit green light while absorbing other colors.
stomata
co2 enters the lead through stomata (tiny pores). 02 exits through these as well.
Calories are tiny unites of energy, so using them to describe the fuel content of foods is not practical:
instead, it is conventional to use kilocalories(kcal), nites of 1000 calories. 1 kilocalorie=1000 calories.
exocytosis
large molecules such as proteins are much too big to fit through the membrane. their traffic into and out of the cell depends on the ability of the cell to package large molecules inside sacs called vesicles. This process is called exocytosis. ex: when you cry, cells in your tears glands use exocytosis to export the salty tears.
osmosis example
left: lower concentration of solute (hypotonic) right: higher concentration of solute (hypertonic) osmosis reduces the difference in sugar concentrations and changes the volumes of two solutions. equal concentrations of solute (isotonic)
conservation of energy
life depends on countless similar conversions of energy from one form to another.
conservation of energy: what are some forms of energy used to do?
some forms of energy are used to perform work, such as moving an object against and opposing force. ex. lifting a barbell against the force of gravity
stroma, thylakoids
stroma= thick fluid in the chloroplasts inner membrane. thylakoids= membranous sacs in stroma. thylakoid STACKS= GRANA.
conservation of energy: energy is defined as
the capacity to cause change
ATP and Cellular Work:
the carbohydrates, fats, and other fuel molecules we obtain from food cannot be used directly as fuel for our cells. Instead, the chemical energy released by the breakdown of organic molecules during cellular respiration is used to generate molecules of ATP. This ATP then powers cellular work. ATP acts like an energy shuttle, storing energy obtained from food and then releasing it as needed at a later time. Such energy transformations are essential for all life on Earth.
the link between glycolysis and the citric acid cycle
the conversion of pyruvic acid to acetyl coa
diver example entropy:
the energy conversions during the climb up the ladder and the dive from the platform increased entropy as the diver emitted heat to the surroundings. to climb up the steps again for another dive, the diver must use additional stored food energy. this conversion will also create heat and therefore increase entropy.
diver example
the friction between the diver's body and its surroundings generated heat in the air and then in the water when the diver hits it.
conservation of energy: what is kinetic energy stored as?
the kinetic energy of muscle movement is stored as potential energy, the energy of an object has because of its location or structure: ex. the energy contained by water behind a dam or by a compressed spring are examples of potential energy
Active Transport: Pumps
•Active transport allows cells to maintain internal concentrations of small solutes that differ from environmental concentrations •For example, compared with its surroundings, an animal nerve cell has a much higher concentration of potassium ions and a much lower concentration of sodium ions •The plasma membrane helps maintain these differences by pumping sodium out of the cell and potassium into the cell •This particular case of active transport (called the sodium-potassium pump) is vital to the nervous system of most animals
energy flow
•All life requires energy •In almost all ecosystems on Earth, this energy originates with the sun •During photosynthesis, plants convert the energy of sunlight to the chemical energy of sugars and other organic molecules •Humans and other animals depend on this conversion for our food and more •From an animal's point of view, photosynthesis is primarily about providing food
cellular respiration
•Both animals and plants use the organic products of photosynthesis as sources of energy •A chemical process called cellular respiration uses O2 to convert the energy stored in the chemical bonds of sugars to another source of chemical energy called ATP •Cells expend ATP for almost all their work •In both plants and animals, the production of ATP during cellular respiration occurs mainly in the organelles called mitochondria
membrane function
•Cells must regulate the flow of materials to and from the environment •The plasma membrane consists of a double layer of fat (a phospholipid bilayer) with embedded proteins •One of the most important functions of the plasma membrane is the regulation of transport in and out of the cell •A steady traffic of small molecules moves across this membrane in both directions •All biological membranes are selectively permeable - that is, they only allow certain molecules to pass
cellular respiration 4
•Cellular respiration is the main way that chemical energy is harvested from food and converted to ATP energy •Cellular respiration is an aerobic process, which is just another way of saying that it requires oxygen •Putting all this together, we can now define cellular respiration as the aerobic harvesting of chemical energy from organic fuel molecules
enzyme inhibitors
•Certain molecules can inhibit a metabolic reaction by binding to an enzyme and disrupting its function •Some of these enzyme inhibitors are substrate imposters that plug up the active site •Other inhibitors bind to the enzyme at a site remote from the active site, but the binding changes the enzyme's shape •In each case, an inhibitor disrupts the enzyme by altering its shape - a clear example of the link between structure and function
cellular respiration 2
•Chemicals, in contrast to energy, are recycled vThe waste products of cellular respiration (CO2, H2O) are the very same ingredients used as inputs for photosynthesis •Plants store chemical energy via photosynthesis and then harvest this energy via cellular respiration •Plants usually make more organic molecules than they need for fuel -This photosynthetic surplus can be stored (as starch in potatoes, for example)
chloroplasts pigments 2
•Chlorophyll a, the pigment that participates directly in the light reactions, absorbs mainly blue-violet and red light •A very similar molecule, chlorophyll b, absorbs mainly blue and orange light •Chlorophyll b does not participate directly in the light reactions, but it conveys absorbed energy to chlorophyll a, which then puts the energy to work in the light reactions
carotenoids
•Chloroplasts also contain a family of yellow-orange pigments called carotenoids which absorb mainly blue-green light •Some carotenoids have a protective function: They dissipate excess light energy that would otherwise damage chlorophyll •Some carotenoids are human nutrients: -beta-carotene (a bright orange/red pigment found in pumpkins, sweet potatoes, and carrots) is converted to vitamin A in the body -lycopene (a bright red pigment found in tomatoes, watermelon, and red peppers) is an antioxidant that is being studied for potential anti-cancer properties
chloroplasts: sites of photosynthesis 2
•Chloroplasts are concentrated in the interior cells of leaves •CO2 enters a leaf, and O2 exits, by way of tiny pores called stomata (singular, stoma, meaning "mouth") •The CO2 that enters the leaf is the source of carbon for much of the body of the plant, including the sugars and starches that we eat •In addition to CO2, photosynthesis requires H2O, which is absorbed by the plant's roots and transported to the leaves, where veins carry it to the photosynthetic cells
carotenoids 2
•Colors of fall foliage are due partly to the yellow-orange light reflected from carotenoids •The decreasing temperatures in autumn cause a decrease in the levels of chlorophyll, allowing the colors of the longer-lasting carotenoids to be seen in all their fall glory
Passive Transport
•Diffusion of molecules across a membrane is an example of passive transport - passive because the cell does not expend any energy for the diffusion to happen •The plasma membrane is relatively impermeable to even some very small substances, such as most ions •In passive transport, a substance diffuses down its concentration gradient, from where the substance is more concentrated to where it is less concentrated -Ex: in our lungs there is more oxygen gas (O2) in the air than in the blood. Therefore, oxygen moves by passive transport from the air into the bloodstream
glycolysis
•During glycolysis, a six-carbon glucose molecule is broken in half, forming two three-carbon molecules vThis initial split requires an energy investment of two ATP molecules per glucose •The three-carbon molecules then donate high-energy electrons to NAD+, forming NADH •In addition to NADH, glycolysis also makes four ATP molecules vGlycolysis thus produces a net of two molecules of ATP per molecule of glucose •What remains of the fractured glucose at the end of glycolysis are two molecules of pyruvic acid that goes into the citric acid cycle
electron transport chain 3
•During the stepwise release of chemical energy in the electron transport chain, our cells make most of their ATP •It is actually oxygen at the end, that makes it all possible •By pulling electrons down the transport chain from fuel molecules, oxygen functions somewhat like gravity pulling objects downhill
the calvin cycle
•The Calvin cycle is the actual sugar-manufacturing machinery, responsible for making sugar from CO2 •This process is called a cycle because its starting material is regenerated
electron transport chain
•Each link in an electron transport chain is actually a molecule, usually a protein •In a series of reactions, each member of the chain transfers electrons •With each transfer, the electrons give up a small amount of energy that can then be used indirectly to generate ATP •The first molecule of the chain accepts electrons from NADH •Thus, NADH carries electrons from glucose and other fuel molecules and deposits them at the top of an electron transport chain
how the light reactions generate atp and nadph
•Energized electrons from the first photosystem pass down an electron transport chain to the second photosystem •The chloroplast uses the energy released by this electron "fall" to make ATP •The second photosystem transfers its light-excited electrons to NADP+, reducing it to NADPH
Fermentation
•Fermentation is the anaerobic harvest of food energy •Although you must breathe to stay alive, some of your cells can work for short periods without oxygen by utilizing fermentation •Under strenuous conditions, your muscles can spend ATP faster than your bloodstream can deliver O2 •This causes your muscle cells to work anaerobically •After functioning anaerobically for about 15 seconds, muscle cells will begin to generate ATP by the process of fermentation
fermentation 2
•Fermentation relies on glycolysis, the first stage of cellular respiration •Glycolysis does not require O2 but does produce two ATP molecules for each glucose molecule •This is not as efficient as the 32 or so ATP molecules each glucose molecule generates during cellular respiration, but it can energize muscles for a short burst of activity •However, in such situations your cells will have to consume more glucose fuel per second because so much less ATP per glucose molecule is generated under anaerobic conditions
water balance in animal cells 2
•For an animal to survive a hypotonic or hypertonic environment, the animal must have a way to balance the uptake and loss of water •The control of water balance is called osmoregulation -Ex: Humans can suffer consequences of osmoregulation failure: Dehydration (consumption of too little water) can cause fatigue and even death -Drinking too much water - called hyponatremia or "water intoxication" - can also cause death by overdiluting necessary ions
Active Transport
•In contrast to passive transport, active transport requires that a cell expend energy to move molecules across a membrane •Cellular energy (usually provided by ATP) is used to drive a transport protein that pumps a solute against the concentration gradient - that is, in the direction that is opposite the way it would naturally flow •Movement against a force, like rolling a boulder uphill against gravity, requires a considerable expenditure of energy
heterotrophs
•In contrast, humans and other animals are heterotrophs ("other-feeders"), organisms that cannot make organic molecules from inorganic ones •Therefore, we must eat organic material to get our nutrients and provide energy for life's processes
endocytosis
•In endocytosis, a cell takes material in via vesicles that bud inward -Ex: in a process called phagocytosis ("cellular eating"), a cell engulfs a particle and packages it within a food vacuole •Endocytosis can also be triggered by the binding of certain external molecules to specific receptor proteins built into the plasma membrane •This binding causes the local region of the membrane to form a vesicle that transports the specific substance into the cell •Cells of your immune system use endocytosis to engulf and destroy invading bacteria and viruses
enzyme inhibitors 2
•In some cases, the binding of an inhibitor is reversible •For example, if a cell is producing more of a certain product than it needs, that product may reversibly inhibit an enzyme required for its production •This feedback regulation keeps the cell from wasting resources that could be put to better use
light reactions
•In the light reactions, chlorophyll in the thylakoid membranes absorbs solar energy (the "photo" part of photosynthesis) •This is then converted to the chemical energy of ATP and NADPH •During the light reactions, water is split, providing a source of electrons and giving off O2 gas as a by-product
photosystems
•In the thylakoid membrane, chlorophyll molecules are organized with other molecules into photosystems •Each photosystem has a cluster of a few hundred pigment molecules, including chlorophylls a and b and some carotenoids •This cluster of pigment molecules functions as a light-gathering antenna •When a photon strikes one of the pigment molecules, the energy jumps from molecule to molecule until it arrives at the reaction center of the photosystem
photosynthesis
•It is the ultimate source of energy for nearly every ecosystem on Earth •It is a process whereby plants, algae, and certain bacteria transform light energy into chemical energy, using CO2 and H2O as starting materials and releasing O2 as a by-product •The chemical energy produced via photosynthesis is stored in the bonds of sugar molecules
photons
•Light behaves as discrete packets of energy called photons •A photon is a fixed quantity of light energy •The shorter the wavelength of light, the greater the energy of a photon vThis is why short-wavelength light, such as ultraviolet light and X-rays, can be damaging •Photons at these wavelengths carry enough energy to damage proteins and DNA, potentially leading to cancerous mutations
chloroplasts: sites of photosynthesis 3
•Like a mitochondrion, a chloroplast has a double-membrane envelope •The chloroplast's inner membrane encloses a compartment filled with stroma, a thick fluid •Suspended in the stroma are interconnected membranous sacs called thylakoids •The thylakoids are concentrated in stacks called grana (singular, granum) •The structure of a chloroplast aids its function by providing a large surface area for the reactions of photosynthesis
Photosynthesis: a two stage process
•Like many energy-producing processes within cells, photosynthesis is a multistep chemical pathway, with each step in the path producing products that are used as reactants in the next step •There are two overall stages of photosynthesis: 1.Light reactions 2.Calvin cycle
enzyme inhibitors 3
•Many beneficial drugs work by inhibiting enzymes: -Penicillin blocks the active site of an enzyme that bacteria use in making cell walls -Ibuprofen inhibits an enzyme involved in sending pain signals •Many cancer drugs inhibit enzymes that promote cell division •Many toxins and poisons also work as inhibitors: -Nerve gases (a form of chemical warfare) irreversibly bind to the active site of an enzyme vital to transmitting nerve impulses, leading to rapid paralysis and death -Many pesticides are toxic to insects because they inhibit this same enzyme
Passive Transport: Diffusion across membranes
•Molecules are restless. They constantly vibrate and wander randomly •One result of this motion is diffusion, the movement of molecules spreading out evenly into the available space •The overall diffusion of molecules is usually directional, from a region where the molecules are more concentrated to a region where they are less concentrated: -Ex: spraying perfume results in the molecules moving out of the bottle (high concentration) and dispersing into the room (low concentration)
producers and consumers
•Most ecosystems depend entirely on photosynthesis for food •For this reason, biologists refer to plants and other autotrophs as producers •Heterotrophs, in contrast, are consumers, because they obtain their food by eating plants or by eating animals that have eaten plants •We animals and other heterotrophs depend on autotrophs for organic fuel and for the raw organic materials we need to build our cells and tissues
the conversion of energy in fuel (food molecules) to a form that cells can use directly
•Most often, the fuel molecule used by cells is C6H12O6, a simple sugar (monosaccharide) •This equation summarizes the transformation of glucose during cellular respiration:
photoautptrophs
•Organisms that generate their own organic matter from inorganic ingredients are called autotrophs •Plants and other organisms that do this by photosynthesis are called photoautotrophs and are the producers for most ecosystems •Not only do photoautotrophs feed us, they also clothe us (as the source of cotton fibers), house us (wood), and provide energy for warmth, light, and transportation (biofuels)
fermentation in microorganisms
•Our muscles cannot rely on lactic acid fermentation for very long •However, the two ATP molecules produced per glucose molecule during fermentation is enough to sustain many other microorganisms •We have domesticated such microbes to transform milk into cheese, sour cream, and yogurt •These foods owe their sharp or sour flavor mainly to lactic acid •The food industry also uses fermentation to produce soy sauce from soybeans, to pickle cucumbers, olives, and cabbage, and to produce meat products like sausage, pepperoni, and salami
chloroplasts: sites of photosynthesis
•Photosynthesis in plants and algae occurs within light-absorbing organelles called chloroplasts •All green parts of a plant have chloroplasts and thus can carry out photosynthesis •In most plants, however, the leaves have the most chloroplasts •Their green color is from chlorophyll, a pigment (light-absorbing molecule) in the chloroplasts that plays a central role in converting solar energy to chemical energy
autotrophs
•Plants and other autotrophs ("self-feeders") are organisms that make all their own organic matter (including carbohydrates, lipids, proteins, and nucleic acids) from nutrients that are entirely inorganic (CO2 from the air, and H2O and minerals from the soil) •Autotrophs make their own food; they don't need to eat to gain energy to power their cellular processes
water balance in plant cells
•Problems of water balance are somewhat different for cells that have rigid cell walls, such as those from plants, fungi, many prokaryotes, and some protists: -A plant cell immersed in an isotonic solution is flaccid (floppy), and the plant wilts -In contrast, a plant cell is turgid (very firm) and healthiest in a hypotonic environment, with a net inflow of water -However, in a hypertonic environment, a plant cell is no better off than an animal cell. As a plant cell loses water, it shrivels, and its plasma membrane pulls away from the cell wall •Therefore a hypertonic environment usually kills the cell •Thus, plant cells thrive in a hypotonic environment, whereas animal cells thrive in an isotonic one
cellular respiration 3
•Respiration on the organismal level should not be confused with cellular respiration, though they are similar •Cellular respiration requires a cell to exchange two gases (CO2, O2) with its surroundings •Respiration, or breathing, results in the exchange of these same gases between your blood and the outside air •O2 is present in the air you inhale, and CO2 in your bloodstream diffuses and exits your body when you exhale
fermentation 3
•Since there is no O2 in glycolysis to accept the electrons from NADH; the NAD+ is regenerated when NADH transfers the electrons it removed from food to pyruvic acid •The addition of electrons to pyruvic acid produces a waste product called lactic acid •The lactic acid by-product is eventually transported to the liver, where liver cells convert it back to pyruvic acid •Exercise physiologists have long speculated about the role that lactic acid plays in muscle fatigue
facilitated diffusion
•Substances that do not cross membranes spontaneously - or otherwise cross very slowly - can be transported via proteins that act as corridors for specific molecules •This assisted transport is called facilitated diffusion -Ex: water molecules can move through the plasma membrane of some cells via transport proteins -other specific transport proteins move glucose across cell membranes 50,000 times faster than diffusion •Even at this rate, facilitated diffusion is a type of passive transport because it does not require the cell to expend energy
electron transport chain 6
•Such a difference in concentration stores potential energy, similar to the way water can be stored behind a dam •There is a tendency for hydrogen ions to gush back to where they are less concentrated, just as there is a tendency for water to flow downhill •The inner membrane temporarily "dams" hydrogen ions
the nature of sunlight
•Sunlight is a type of energy called radiation or electromagnetic energy •Electromagnetic energy travels through space as rhythmic waves, like the ripples made by a pebble dropped into a pond •The distance between the crests of two adjacent waves is called a wavelength •The full range of radiation, from the very short wavelengths of gamma rays to the very long wavelengths of radio signals, is called the electromagnetic spectrum •Visible light is the fraction of the spectrum that our eyes see as different colors
calvin cycle
•The Calvin cycle uses the products of the light reactions to power the production of sugar from CO2 •The enzymes that drive the Calvin cycle are dissolved in the stroma •ATP generated by the light reactions provides the energy for sugar synthesis •The NADPH produced by the light reactions provides the high-energy electrons that drive the synthesis of glucose from CO2 •Thus, the Calvin cycle indirectly depends on light to produce sugar because it requires the supply of ATP and NADPH produced by the light reactions
cellular respiration 5
•The Citric acid cycle (also called the Krebs cycle) completes the breakdown of glucose all the way to CO2, which is then released as a waste product •The enzymes for the Citric acid cycle are dissolved in the fluid within mitochondria •Glycolysis and the citric acid cycle generate a small amount of ATP directly •They generate much more ATP indirectly, via reactions that transfer electrons from fuel molecules to a molecule called NAD+ (nicotinamide adenine dinucleotide) that cells make from niacin, a B vitamin
Photosynthesis
•The chemical ingredients for photosynthesis are CO2, a gas that passes from the air into a plant via tiny pores, and H2O, which is absorbed from the soil by the plant's roots •Inside leaf cells, organelles called chloroplasts use light energy to rearrange the atoms of these ingredients to produce sugars - most importantly glucose (C6H12O6) - and other organic molecules •A by-product of photosynthesis is O2 that is released through pores into the atmosphere
citric acid cycle
•The citric acid cycle finishes extracting the energy of sugar by dismantling the acetic acid molecules all the way down to CO2 •Acetic acid joins a four-carbon acceptor molecule to form a six-carbon product called citric acid (for which the cycle is named) •The citric acid cycle harvests energy from the fuel, some of which is used to produce ATP directly •The cycle captures much more energy in the form of NADH and a second, closely related electron carrier called FADH2 •Because glycolysis splits glucose in two, the citric acid cycle occurs twice for each glucose molecule that fuels a cell
Osmosis and Water Balance
•The diffusion of water across a selectively permeable membrane is called osmosis •A solute is a substance that is dissolved in a liquid solvent, and the resulting mixture is called a solution •Water will diffuse across the plasma membrane along its concentration gradient from an area of higher water concentration (hypotonic solution) to one of lower water concentration (hypertonic solution) •This reduces the difference in solute concentrations and changes the volumes of the two solutions
cellular respiration 6
•The electron transfer forms a molecule called NADH that acts as a shuttle carrying electrons through the cell •The third stage of cellular respiration is electron transport: -electrons captured from food by the NADH formed in the first two stages are stripped of their energy, a little bit at a time, until they are finally combined with oxygen to form water •The proteins and other molecules that make up electron transport chains are embedded within the inner membrane of the mitochondria •The transport of electrons from NADH to oxygen releases the energy your cells use to make most of their ATP
electron transport chain 2
•The electrons cascade down the chain, from molecule to molecule, like an electron bucket brigade •The molecule at the bottom of the chain finally "drops" the electrons to oxygen •At the same time, oxygen picks up hydrogen, forming water •The overall effect of all this transfer of electrons during cellular respiration is a "downward" trip for electrons from glucose to NADH to an electron transport chain to oxygen
carbon fixation
•The initial incorporation of carbon from CO2 into organic compounds is called carbon fixation •This process has important implications for global climate, because the removal of carbon from the air and its incorporation into plant material can help reduce the concentration of CO2 in the atmosphere •Deforestation removes photosynthetic plant life, thereby reducing the ability of the biosphere to absorb carbon •This increases the effect of the gases that contribute to global climate change
Stages of Cellular Respiration
•The many chemical reactions that make up cellular respiration can be grouped into three main stages: 1.Glycolysis 2.Citric acid cycle 3.Electron transport •During glycolysis, a molecule of glucose is split into two molecules of a compound called pyruvic acid •The enzymes for glycolysis are located in the cytoplasm
electron transport chain 5
•The molecules of electron transport chains are built into the inner membranes of mitochondria •Because these membranes are highly folded, their large surface area can accommodate thousands of copies of the electron transport chain •Each chain acts as a chemical pump that uses the energy released by the "fall" of electrons to move hydrogen ions (H+) across the inner mitochondrial membrane •This pumping causes ions to become more concentrated on one side of the membrane than on the other
an overview of photosynthesis
•The opposite of cellular respiration occurs in photosynthesis: -electrons are boosted "uphill" and added to CO2 to produce sugar -hydrogen is moved along with the electrons being transferred from water to CO2 •This transfer of hydrogen requires the chloroplast to split water molecules into hydrogen and oxygen -The hydrogen is transferred along with electrons to CO2 to form sugar -The oxygen escapes through stomata in leaves into the atmosphere as O2, a waste product of photosynthesis
cellular respiration 7
•The overall equation for cellular respiration shows that the atoms of the reactant molecules glucose and oxygen are rearranged to form the products carbon dioxide and water •The main function of cellular respiration is to generate ATP for cellular work •The process can produce around 32 ATP molecules for each glucose molecule consumed
photosystems reaction center
•The reaction center consists of chlorophyll a molecules that sit next to another molecule called a primary electron acceptor •This primary electron acceptor traps the light-excited electron from the chlorophyll a in the reaction center •Another team of molecules built into the thylakoid membrane then uses that trapped energy to make ATP and NADPH
chloroplasts pigments
•The selective absorption of light by leaves explains why they appear green to us •Light of that color is poorly absorbed by chloroplasts and is thus reflected or transmitted toward the observer •Energy cannot be destroyed, so the absorbed energy must be converted to other forms •Chloroplasts contain several different pigments that absorb light of different wavelengths
water balance in animal cells
•The survival of a cell depends on its ability to balance water uptake and loss •When an animal cell is immersed in an isotonic solution, the cell's volume remains constant because the cell gains water at the same rate that it loses water •However in a hypotonic solution, which has a lower solute concentration than the cell, the cell would gain water, swell, and possibly burst (lyse) due to osmosis •A hypertonic environment is also harsh on an animal cell; the cell shrivels from water loss
the conversion of pyruvic acid to acetyle coA
•The two molecules of pyruvic acid from glycolysis, are not quite ready for the citric acid cycle (CAC) •The pyruvic acid must be converted to a form the CAC can use •Through several reactions, the pyruvic acid is converted to acetic acid and attached to a molecule called coenzyme A (CoA) forming acetyl CoA •The CoA escorts the acetic acid into the first reaction of the CAC •The CoA is then stripped and recycled
light reactions in the thylakoids membrane
•The two photosystems and the electron transport chain that connects them transfer electrons from H2O to NADP+, producing NADPH •The mechanism of ATP production during the light reactions is very similar to the mechanism we saw in cellular respiration: -In both cases, an electron transport chain pumps hydrogen ions (H+) across a membrane -In both cases, ATP synthases use the energy stored by the H+ gradient to make ATP
electron transport chain 4
•This role as a final electron acceptor is how the oxygen we breathe functions in our cells and why we cannot survive more than a few minutes without it •Viewed this way, drowning is deadly because it deprives cells of the final "electron grabbers" (oxygen) needed to drive cellular respiration
how photosystems harvest light energy
•When a pigment molecule absorbs a photon, one of the pigment's electrons gains energy •This electron is now said to be "excited" •The excited state is highly unstable, so an excited electron usually loses its excess energy and falls back to its ground state almost immediately
Enzyme Activity 2
•When a substrate slips into this docking station, the active site changes shape slightly to embrace the substrate and catalyze the reaction •This interaction is called induced fit because the entry of the substrate induces the enzyme to change shape slightly, making the fit between substrate and active site snugger
the nature of sunlight 2
•When sunlight shines on a pigmented material, certain wavelengths (colors) of the visible light are absorbed and disappear from the light that is reflected by the material •For example, we see a pair of jeans as blue because pigments in the fabric absorb the other colors, leaving only light in the blue part of the spectrum to be reflected from the fabric to our eyes •In the 1800s, botanists (biologists who study plants) discovered that only certain wavelengths of light are used by plants
osmosis and water balance 2
•When the solute concentrations are the same on both sides of a membrane, water molecules will move at the same rate in both directions, so there will be no net change in solute concentration •Solutions of equal solute concentration are said to be isotonic -Ex: many marine animals, such as sea stars and crabs, are isotonic to seawater, so that overall they neither gain nor lose water from the environment. -In hospitals, intravenous (IV) fluids administered to patients must be isotonic to blood cells to avoid harm
calvin cycle 2
•With each turn of the cycle, there are chemical inputs and outputs: -The inputs are CO2 from the air as well as ATP and NADPH produced by the light reactions -Using carbon from CO2, energy from ATP, and high-energy electrons from NADPH, the Calvin cycle constructs an energy-rich sugar molecule called glyceraldehyde 3-phosphate (G3P) •The plant cell can then use G3P as the raw material to make glucose and other organic compounds (ex: cellulose and starch) that it needs
fermentation in yeast
•Yeast, a microscopic fungus, is capable of both cellular respiration and fermentation •When kept in an anaerobic environment, yeast cells ferment sugars and other foods to stay alive •As they do, the yeast produce ethyl alcohol as a waste product instead of lactic acid •This alcoholic fermentation also releases CO2 •For thousands of years, people have put yeast to work producing alcoholic beverages such as beer and wine •The CO2 bubbles from fermenting yeast also cause bread dough to rise
atp synthase
•Your mitochondria have structures that act like turbines •Each of these miniature machines, called an ATP synthase, is constructed from proteins built into the inner mitochondrial membrane, adjacent to the proteins of the electron transport chains •The H+ concentrated on one side of the mitochondrial membrane rushes back "downhill" through an ATP synthase •This action spins a component of the ATP synthase, just as water turns the turbines in a dam •The rotation activates parts of the synthase molecule that attach phosphate groups to ADP molecules to generate ATP
