Cell Membrane, Cell Transport, Origins of Life
Spontaneous generation
old theory that believed in the formation of living organisms from non-living matter.
When temperatures rise, the cholesterol...
prevents rips in the membrane from occurring by holding the phospholipids together.
When temperatures lower, the cholesterol...
prevents the membrane from freezing solid, by acting as a spacer between the phospholipid molecules.
SA:V =
6S^2/S^3 S is a side length.
Computer Models
A computer program which attempts to simulate the behavior of a particular system.
Model
A representation of an idea, an object, a process or a system that is used to describe and explain phenomena.
Electron Microscopes
Because electron microscopes have a much higher resolution than light microscopes, the invention of the electron microscope in the 1930's led to greater understanding of cell structures such as the cell membrane.
Bulk Transport in Cells
Because the membrane is "fluid" cells can transport of many molecules into ("endo") or out of ("exo") the cell at once.
Why are cubes used to model the relationship between surface area and volume?
Because the relationship is the same in both cubes and cells.
Structure of Urea
C double bonded to an O and single bonded to two NH2
Types of Scientific Models
Mathematical Models, Computer Models, Physical Models, Images, Analogies
Which organelle in freshwater protist like amoeba, prevents the cell from exploding by actively pumping water that enters in via osmosis out of the cell?
contractile vacuole
Osmoregulation
control of the water balance of a living organism.
Singer-Nicholson model
current model of membrane structure that incorporates a fluid mosaic structure in a discontinuous lipid bilayer.
Facilitated diffusion
diffusion through a membrane that requires proteins.
If you soak your hands in dishwater, you may notice that your skin absorbs water and swells into wrinkles. This is because your skin cells are _______________ to the _______________ dishwater.
hypertonic...hypotonic
You decide to buy a new fish for your freshwater aquarium. When you introduce the fish into its new tank, the fish swells up and dies. You later learn that it was a fish from the ocean. Based on what you know of tonicity, the most likely explanation is that the unfortunate fish went from a(n) __________ solution into a(n) __________ soution.
isotonic..hypotonic
Which organ(s) regulates osmolarity in human bodies?
kidneys
Micelles
lipid molecules orient with polar (hydrophilic) head toward water and nonpolar (hydrophobic) tails away from water
micelle
lipid molecules that arrange themselves in a spherical form in aqueous solutions
The fluidity of membranes allows...
materials to be taken into cells by endocytosis or released by exocytosis.
Semi-permeable membrane
membrane that allows some substances to diffuse through but not others. Transport pumps proteins in the plasma membrane that use ATP to move substances across the membrane. Vesicles a bubble-like membranous structure that stores and transports cellular products.
Diffusion
passive movement of particles from a region of higher concentration to a region of lower concentration.
Osmosis
passive movement of water molecules from a region of lower solute concentration to a region of higher solute concentration.
In diffusion, the phospholipid bilayer must be...
permeable to the particle.
Exocytosis
the process in which the cell releases materials to the outside by discharging them as membrane-bounded vesicles that pass through the cell membrane.
Spallanzani
used broth to disprove spontaneous generation
Adaptations of cells that maximize the SA: volume ratio: List Examples of Long Extensions of the Cell Membrane
- Dendritic cell of mammal immune system. - Neuron cell of a chordate nervous system. - Epidermis cell forming a root hair in a plant.
Surface Area To Volume Ratio Graph
A large cell has less SA:V ratio. A small cell has more SA:V ratio.
Vesicle
A membrane bound sac that contains materials involved in transport of the cell.
Calculate the percent change in mass of each tissue sample.
% change = ((final-initial)/initial)*100 - the pieces of tissue will not all be the same mass as the were at the beginning of the experiment - the change in mass indicates whether the tissue has gained or lost water - using percent change allows you to compare the relative changes in mass, since the initial samples were likely not all the identical starting mass
Polymer
"many parts" A large molecule composed of many monomer subunits.
Monomer
"one part" The single building block unit of a polymer.
Why did ideas of spontaneous generation persist for thousands of years?
- Early philosophers and scientists were basing their ideas on what they could observe at the time, like in this 16th century depiction of spontaneous generation of honey bees from a dead ox. - Technological tools had not yet advanced to the point of being able to observe cells arising from other cells. - Human tendency to take cues for thought and behavior from others rather than exercise our own independent judgment. Everyone at the time thought spontaneous generation was accurate, so there was no reason or pressure to show that it wasn't. It's hard to speak out against an idea when a majority support it. - Spontaneous generation was consistent with the other widely held cultural and religious beliefs of the time. "Scientists" of the time were often affiliated and advocates of religious doctrine.
Earth History Timeline
- Formation of Earth - Chemical Evidence of Life - Visible Evidence of Life - Biomarkers of Life - Great Oxygenation Event - Origin of Eukaryotic Cells - Origin of Chloroplasts - First Animals - First Land Plants - Early Mammals - Dinosaur Extinction - Humans
Discuss implications of all cells being formed from preexisting cells.
- Implication #1: We can trace the origin of all the cells in our body back to the first cell; the zygote produced by the fertilization of a sperm and egg. - Implication #2: The origins of all cells can be traced back through billions of years of evolution to "LUCA" the last universal common ancestor of all life on Earth. -Implication #3: There must have been a first cell that arose from non-living material.
Examples of Endocytosis
- Macrophages (a type of white blood cell) can engulf pathogens when fighting infection. - Single celled organism like amoeba can engulf other organisms as a food source. - Additionally, endocytosis was an important step in the Theory of Endosymbiosis, which lead to the origin of eukaryotic cells.
Protein Pumps
- Molecule to be transported enters the pump - Energy from ATP is used to change the shape of the protein - Molecule can now pass to the opposite side of the membrane
Adaptations of cells that maximize the SA: volume ratio: List Examples of Thin Flattened Shape
- Red blood cell - Type 1 pneumocyte in alveoli - Epithelial cell forming a capillary tube
Examples of Exocytosis
- Secretion of neurotransmitter at synaptic terminus. - Secretion of hormones from endocrine glands, such as insulin and glucagon from the pancreas - Secretion of digestive juices from exocrine glands in the mouth, stomach, and pancreas. - Secretion of blood plasma proteins such as fibrinogen from the liver. - Release of cortical granules from egg cell during fertilization, preventing polyspermy
Adaptations of cells that maximize the SA: volume ratio: List Examples of Bristle Like Extensions Called MIcrovilli
- Small intestine epithelial cell - Cell of the kidney proximal convoluted tubule - White blood cell
What does the fluidity of the membrane allow for?
- formation of vesicles - materials to be taken into cells by endocytosis or released by exocytosis - Pinching in of the cell membrane during animal cell cytokinesis
As a cell becomes too large...
...the surface area to volume ratio becomes too small.
The apparatus used for Miller-Urey's original experiment.
1. Boiled water evaporates and moves into the larger flask, where it combines with .... 2. ... methane, ammonia and hydrogen gases in a large flask. Sparks are fired between electrodes to simulate lightning. 3. A cooling condenser turns steam back into liquid water, which drips down... 4. ....into the trap, where organic molecules produced in the reactions also settle.
Some cells increase surface area to volume ratio by having:
1. Long cellular extensions that increase surface area without large increase in volume (e.g. nerve cells) 2. Thin, flat cell shapes that increase surface area without large increase in volume (e.g. red blood cells) 3. Extensions of the cell membrane that increase surface area without large increase in volume (e.g. microvilli on small intestine cells)
How can Osmolarity of a tissue be determined experimentally?
1. Mass samples of tissues. 2. Place samples of a tissue in solutions of known osmolarity 3. Let the samples sit for a set amount of time. 4. Re-mass the tissue samples.
Outline the four processes needed for the spontaneous origin of cells on Earth.
1. SYNTHESIS - The synthesis of simple organic molecules from inorganic compounds. 2. POLYMERIZATION - The assembly of these organic molecules into polymers. 3. SELF-REPLICATION - The formation of a polymer that can self replicate (enabling inheritance). 4. PACKAGING - Packaging of molecules into membranes with an internal chemistry different from the surroundings.
Friedrich Wohler
1828 synthesized urea (organic) from ammonium cyanate (inorganic)
Analogies
A comparison between two things, typically on the basis of their structure and for the purpose of explanation or clarification
Amphipathic
A single molecule that contains both hydrophilic and hydrophobic parts.
Normal Saline Definition
A solution of water and salt ions that is isotonic to human blood. Because the solution is isotonic to body cells, the cells will not shrink or swell when exposed to the saline solution.
Insulin Receptor Protein
A type of receptor protein. Insulin is a hormone released by the pancreas when blood sugar levels are high. Insulin binds to the insulin receptor protein, which then causes the cell to open the typically closed glucose transport protein. This allows glucose to enter the cell from the blood.
Active Transport Examples in Plants: Phloem Sieve Tubes
Active transport is used to load organic compounds into phloem sieve tubes at the source, initiating transport of sugars around the plant body
Active Transport Examples in Plants: Roots
Active uptake of mineral ions in the roots causes absorption of water by osmosis.
Cadherins
Adhesian protein example. A type of transmembrane protein. In the presence of calcium-binds cells within tissues together.
Pneuma
Air
What does the plasmic membrane regulate?
All cells have an outer plasma membrane that regulates not only what enters the cell, but also how much of any given substance comes in.
Early Observations of the Cell Membrane
Although it could not be observed under the light microscope, early cell biologists quickly grasped that something must exist that effectively separates the inside of the cell from its external environment. They also realized that this structure would be more than a simple barrier since it obviously let some substances pass while it blocked others. Moreover, the rate at which it let materials pass often varied over time.
Adhesion Proteins
Anchors the cell membrane to the inner cytoskeleton or proteins outside the cell as well as to other cells. Can be integral or peripheral.
Describe the relationship between cell size and the SA:V ratio of the cell.
As a cell grows bigger, its internal volume enlarges and the cell membrane surface area expands. However, the volume increases more rapidly than does the surface area, and so the amount of surface area relative to the volume (SA:V) decreases. Small cells have lots of surface area relative to the total volume of the cell. As a cell gets bigger, there is less surface area relative to the total volume of the cell
Explain why cells are often limited in size by the SA:V ratio.
As a cell grows, eventually the surface area can no longer serve the requirements of the cell (nutrients in and waste out through the cell membrane). A decreasing surface area to volume ratio will stimulate cell division through mitosis or binary fission. By dividing, the size of the cell is reduced and kept within SA:V limits.
Why might fatty acids not make the best membranes?
At a molecular level, fatty acids are extremely dynamic, and are constantly entering and exiting the vesicle bilayer, as well as flipping between the inner and outer leaflet of the membrane.
What is membrane fluidity affected by?: Temperature
At higher temperatures, the membrane has more fluidity than at lower temperatures.
Why is it important to know the osmolarity of tissues?
Because tissues or organs used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis.
What did believers in vitalism predict?
Believers of vitalism predicted that molecules produced in living things require the "vital force" and therefore could not be synthesised from simple inorganic components.
Scientific Models
Explain observations, predict future observations, are realistic. Models are conceptual representations used to explain and predict phenomena. Models are developed to explain processes that may not be observable or when experimentation is not possible.
Finding Osmolarity from a graph
By plotting the percent change in mass of the tissue sample in the different solutions, the osmolarity of the tissue can be determined. The osmolarity of a tissue is the point at which there is no change in mass. On the graph, this is the osmolarity extrapolated from the point at which a best fit line through the points crosses the 0% change line. WHEN IT CROSSES X-AXIS; Y=0.
Examples of Facilitated Diffusions
CFTR Channel moves chloride ions out of the cell, Sodium (Na+) and potassium (K+) channels, small intestine.
Active Transport Examples in Plants: Auxin Efflux Pumps
Can set up concentration gradients of auxin in plants tissue, allowing plants to respond to the environment by tropisms.
Molecules out of Cell
Carbon dioxide gas Urea (waste from metabolism)
Why are cells small?
Cells are typically small because of the ratio of surface area to volume.
Glucose Channel Protein
Channel protein example. Glucose is too large and too hydrophilic to diffuse naturally through the phospholipid bi-layer. Glucose needs a channel protein in order to do this. Notice in the picture glucose is moving from a high to low concentration, so no energy is required.
Which cells is cholesterol found in and why?
Cholesterol tends to be found in high quantities in animal cells versus plant/fungi/bacteria. This is because animal cells don't have a cell wall to maintain their structure, but still need to be flexible (fluid). Cold blooded animals (who can't regulate body temperatures) tend to have more cholesterol than warm-blooded.
Explain the benefits of using cubes to model the surface area and volume of a cell.
Cubes can be manipulated, visualized and easily measured whereas cells are difficult to to manipulate and measure because of their microscopic size and variability in shape.
Isotonic
Describes a solution whose solute concentration is equal to the solute concentration inside a cell. There will be no NET water movement and the cell will remain the same size.
Examples of Diffusion
Diffusion of CO2 and O2 into and out of lung alveoli. Diffusion of CO2 and O2 into and out of eye cornea cells.
Receptor Proteins
Each type binds to a specific molecule found outside the cell (like a hormone) which triggers a change inside the cell, or a cell action. Can be integral/peripheral
Simple Time Scale of Earth
Earth forms, Water condenses/cools, Prebiotic chemistry emerges, "RNA World" forms, First DNA/Protein life forms, life diversifies
ATP Synthase
Enzyme Protein Example. An important enzyme that provides energy for the cell by synthesizing adenosine triphosphate (ATP) Works by adding a phosphate onto adenosine diphosphate (ADP) to create ATP. Located in the membranes of chloroplasts and mitochondria (used in both photosynthesis & respiration) and the cell membranes of some prokaryotes.
Jan Baptist van Helmont Historical Thinking About Spontaneous Generation
European chemist and physician. van Helmont (1579-1644) placed a dirty shirt in with some wheat and mice "appeared" 21 days later. According to van Helmont the sweat in the shirt was the active element which gave life to the inert matter.
Miller-Urey Experiment
Experiment that found that organic molecules can form in a strongly reducing atmosphere.
Outline why fatty acids were likely the primary component of the membrane of early cells.
Fatty acids spontaneously form micelles. Research in the Szostak lab has shown that at higher concentrations and under the appropriate pH conditions, fatty acids micelles can form vesicles, capturing fluids and dissolved molecules, Once formed, fatty acid vesicles are highly stable, and appear outwardly unchanging over the course of days or even months.
What was likely the primary component of early membranes? Why?
Fatty acids. Fatty acids are structurally much simpler than phospholipids and may have formed more readily in a prebiotic environment.
Membrane Fluidity
Fluidity refers to the viscous flow of phospholipids in the cell membrane and organelles of the endomembrane system.
Fluorescent Antibody Tagging
Fluorescent marker molecules were attached to membrane proteins (essentially "coloring" the proteins in the membrane so they could be seen). Two cells labeled with different membrane-bound fluorescent tags were fused Within 40 minutes the differently colored proteins were mixed throughout the membrane of the fused cell. Shows that membrane proteins can move around, they are not locked in place as would have been suggested by the Davson and Danielli model.
Why do we use cubes to model SA:V ratio?
For simplicity of the math. In real life cells are more like spheres, but the concept remains the same.
Freeze-etched Electron Micrographs:
Freeze etching is an electron microscopic preparation technique that was developed in the 1960's. The technique involves rapid freezing of cells and then fracturing them along lines of weakness, including through the center of membranes. Freeze etching suggested that proteins can span through the lipid bilayer, not just on top of it (as suggested by Davson and Danielli).
Louis Pasteur
French scientist that proved, among other things, that the emergent growth of bacteria in nutrient broths is due to biogenesis, not spontaneous generation.
Molecules into cell
Glucose and Oxygen Gas
Tissues will have different osmolarities because they:
Have different dissolved solutes (sugars, salts, proteins) May have been grown in different soils giving their tissues different contents May have been stored under different conditions May be more or less dehydrated May be different ages May be different tissue types
Hypertonic
Having a higher concentration of solute than another solution. More solutes outside the cell than inside; less water outside the cell than inside. Cell shrinks.
Hypotonic
Having a lower concentration of solute than another solution. Less solutes outside the cell than inside; more water outside the cell than inside. Cell grows.
Fluid Phase
High temperatures. Bilayer "melts"; movement is allowed.
Water always moves from a __________ to a __________ solution.
Hypertonic Hypotonic
Osmosis in Medicine
IV solutions and solutions used to keep organs alive during transplant must have the same osmolarity as the cytoplasm as the cells to prevent osmosis.
Deduction of the Artificial Urea Synthesis
If urea can be synthesized without a vital force, other organic compounds could be as well Processes in living organisms are governed by the same chemical and physical forces as in non-living matter
Evidence Against Davson and Danielli
Improvements in biochemical techniques allowed proteins to be extracted from membranes. The proteins were found to be: varied in size, unlike the type of protein that would form continuous layers on the outside of the membrane as Davson and Danielli had proposed. hydrophobic on at least part of their surface, unlike the completely hydrophilic proteins on the outside of the membrane as Davson and Danielli had proposed.
Francesco Redi
In 1668, Francesco Redi, an Italian scientist, designed an experiment to test spontaneous generation of maggots. Redi is credited with performing one of the first controlled experiments.
Lazzaro Spallanzani
In 1768, Lazzaro Spallanzani , an Italian priest and scientist, designed an experiment to test spontaneous generation of microbes. Spallanzani performed other experiments to discredit the idea of spontaneous generation, notably an experiment in which male frogs wore little shorts while mating... read more here! His work with frogs is immortalized in a marble statue found in Italy!
Artificial Urea Synthesis
In 1828, German chemist Friedrich Wohler synthesized urea artificially. Cyanic acid + ammonia -> urea
Endocytosis
In endocytosis, the cell activity transports molecules into the cell by engulfing them into vesicles formed from the cell membrane. The plasma membrane folds inward forming a cavity that fills with extracellular fluid, dissolved molecules, food particles, foreign matter, pathogens, or other substances. The plasma membrane folds back on itself until the ends of the in-folded membrane meet. This traps the fluid inside the vesicle. The vesicle is pinched off from the membrane as the ends of the in-folded membrane fuse together. The vesicle breaks away from the cell membrane and moves into the cytoplasm. The cell membrane has gotten smaller.
Cholesterol
In eukaryotes, a fat molecule called cholesterol modulates the membrane fluidity by making the membrane: Less fluid at warmer temperatures More fluid at lower temperatures Cholesterol does this by binding adjacent phospholipids together.
Exocytosis
In exocytosis, the cell activity transports molecules out of the cell into the extracellular space. - Vesicles containing molecules are transported from within the cell to the cell membrane. - The vesicle membrane attaches to the cell membrane. - Fusion of the vesicle membrane with the cell membrane releases the vesicle contents outside the -Cell membrane has grown larger. The molecules in vesicles are typically proteins made on bound ribosomes hat: Are secreted to the extracellular environment such as hormones or digestive enzymes Bound to the vesicle membrane and will become part of the cell membrane such as channels, pumps, or receptors.
Protocells
In his lab, Martin Hanczyc makes experimental blobs of chemicals that behave like living cells. His work demonstrates how cells may have had first occurred on Earth.
How is urea synthesized in the body?
In humans, the liver converts ammonia (NH3, toxic byproduct of protein metabolism) to urea which is excreted from the body via the kidneys.
Active Transport Examples: Proton Pump
In order for cells to perform photosynthesis and/or cellular respiration, protons (also known as H+ ions) must be pumped across the inner membranes of the mitochondria or chloroplast.
How did the Oparin-Haldane hypothesis come about?
In the 1920s, Alexander Oparin and J. B. S. Haldane independently proposed nearly identical hypotheses for how life originated on Earth. Their hypothesis is now called the Oparin-Haldane hypothesis.
Osmosis in the Body
In the KIDNEY nephron, the loop of Henle is surrounded by tissue fluid which has a high concentration of ions in it (hypertonic). This causes water to move out of the descending limb by osmosis. Water moves via osmosis from the SMALL and LARGE INTESTINE into the blood.
Molecules that can move through the phospholipid bilayer.
In the case of the cell membrane, permeable molecules are usually small, non-charged particles like oxygen and carbon dioxide
Active Transport Examples in Animal Physiology: Kidney
In the kidney, the proximal convoluted tubule selectively reabsorbs useful substances by active transport.
Active Transport Examples in Animal Physiology: Small Intestine
In the small intestine, glucose, amino acids, Na, Ca, and Fe ions are absorbed into the cells by active transport
Emergent Property
Individual parts, such as parts of the cell (not alive), are arranged into a structure (alive).
Normal Saline Uses
It is used as an eye wash, to flush wounds and intravenously to rehydrate patients. During organ transplant, while out of a body the organs are bathed in normal saline. The solution must have the same osmolarity as the cytoplasm of the cells to prevent cell death due to osmosis.
Explain why cells are often limited in size by the SA:V ratio. (Large cells)
Large cell has smaller SA:V ratio. Large volume requires many metabolic nutrients and waste to be transported through the cell membrane. However there is relatively less cell membrane for transporting materials into/out of the cell. Within the cell, molecules have larger distance to diffuse.
What is membrane fluidity affected by? Fatty Acid Length
Longer fatty acid tails allow for more interactions between phospholipids, leading to less fluidity.
Gel Phase
Low temperatures. Hydrocarbons are tightly packed.
Gorter and Grendel
Membranes are a lipid bilayer made of phospholipids with hydrophilic heads and hydrophobic tails. DEDUCED that the plasma membrane is a lipid bilayer made of phospholipids with hydrophilic heads and hydrophobic tails...Gorter and Grendel proposed a structure for the bilayer, with the polar hydrophilic heads facing outwards towards the aqueous environment and the hydrophobic tails facing inwards away from the aqueous surroundings on both sides of the membrane. Extracted phospholipids from the cell membrane of red blood cells Calculated that the surface area of the phospholipids when arranged in a monolayer was twice as large as the surface area of the intact red blood cell. Gorter and Grendel hypothesized that if the plasma membrane is a bilayer, then then its surface area should be half that occupied by all its lipids spread out in a monolayer. Their process: 1. They measured the total surface area of the plasma membrane of red blood cells under a microscope. 2. They extracted the lipids from the cells, spread the lipids as a monolayer, and then again measured the surface area of the lipids. 3. Comparison of these two measurements produced a cell:monolayer surface area ratio of approximately 1:2 for a number of different mammalian red cells, supporting their hypothesis.
Overton
Membranes are made up of lipids. Is regarded as a pioneer in the understanding of the structure and function of the cell membrane. Overton proposed a membrane model which stated that biological membranes are made up of lipids. Overton also concluded that the cell membrane is semipermeable, meaning some materials could pass through the membrane while others could not. Before this discovery it was believed that the membrane was impermeable to almost anything but water.
Membranes must be fluid to work properly!!!!!
Membranes must be fluid enough for the cell to move. Membranes need to be fluid enough for the required substances to move across them. Membranes if too fluid however, won't be able to regulate effectively what substances move in and out (think of holes or rips occurring in the membrane).
What proves the endosymbiotic theory?
Mitochondria and chloroplasts have circular, single stranded DNA.
Why are models used in science?
Models can simplify complex structures and processes. Models can change the scale of objects that are too big or too small to see at all. Models can change the rate of a phenomenon; slow it down or speed it up. Models can help us communicate by simplifying difficult concepts and/or making concepts more tangible. Scientists use models (e.g. computer models) to make and test predictions and to understand processes that are not visible or easily observed.
Physical Models
Models of structures that can be carried, touched, or held.
Facilitated Diffusion
Molecules move through a channel protein in the membrane. Used for small charged molecules (ions). Passive. High to low concentration.
What can monomers do? Examples.
Monomers may have been able to spontaneously form polymers on early Earth. Amino acids can spontaneously link together to form proteins. RNA nucleotides can link together when exposed to a catalyst found in clay or in water.
Examples of Facilitated Diffusion: Small Intestine
Monosaccharides like fructose and some other small hydrophilic molecules are absorbed by facilitated diffusion into the small intestine.
Explain the limitations of using cubes to model the surface area and volume of a cell.
Most cells are not cubic in shape.
What are the limitations of models?
No model can possibly explain every detail of a phenomena. While a model is a similar substitute for what it represents, it can only relate to some properties of the target, as some aspects of the target must be excluded from the model. Therefore, models are not copies: they are similar to what they represent, but they are not the same as what they represent. A good model must be able to represent as many characteristics of reality as possible, but also be as simple as possible. Like anything in science, models come under scrutiny and change over time. Models can only be as accurate as the current state of scientific knowledge about the phenomenon they describe. Models tested against experiments or data from observations may prove inadequate, in which case they may be modified or replaced by new models.
How life emerges from parts in a Eukaryotic Cell
Non-living parts come together. The individual parts are arranged into a structure. Emergent behavior results.
Hydrophobic
Nonpolar molecules that are incapable of forming bonds with water molecules; Repel the water molecules.
Peripheral Proteins
Not embedded- attached to one surface of the membrane. Attach only temporarily to the cell membrane. Sometimes attach to integral proteins.
Miller and Urey concluded that...
Organic molecules, including amino acids, can form from inorganic compounds* Organic molecules could have formed on prebiotic Earth.
Historical Models of the Cell Membrane in Order
Overton, Gorter and Grendel, Davson and Danielli, Singer and Nicolson
Diffusion of CO2 and O2 into and out of lung alveoli. Information and draw picture.
Oxygen and carbon dioxide move through Type 1 pneumocytes into the alveoli
Swan Neck Flasks
Pasteur made a series of flasks with long, twisted necks ("swan-neck" flasks), in which he sterilized broth by boiling it. The design allowed air inside the flasks to be exchanged with air from the outside, but prevented the introduction of any airborne microbes. Boiling the broth kills the microorganisms. The curve of the flask prevents outside air from entering the flask. No contamination occurs. When the neck of the flask is broken off, bacteria reach the sterile broth, and organism growth occurs.
Describe Pasteur's Experiment
Pasteur's experiment consisted of two parts. In the first part, the broth in the flask was boiled to sterilize it. When this broth was cooled, it remained free of microbial contamination. In the second part of the experiment, the flask was boiled and then the neck was broken off. The broth in this flask became contaminated with microbes.
What did the outcome of Pasteur's experiments show?
Pasteur's experiments (1859) provided evidence that spontaneous generation of cells and organisms does not now occur on Earth. If a life force was responsible for microbial growth within the sterilized flasks, it would have access to the broth, whereas the microorganisms would not. However, because the broth in the flask remained clear, Pasteur's experiment showed that air does not contain a "vital force" that creates life. Life could not spontaneously generate.
Why called a FLUID?
Phospholipid bilayer is flexible, allowing for cellular shape changes. Membrane lipids (and some proteins) can drift laterally within the membrane. Individual phospholipid molecules are not bonded to one another. Proteins drift more slowly than lipids. Some membrane proteins are tethered to the cytoskeleton and cannot move far.
How are phospholipids synthesized?
Phospholipids are synthesized by the smooth endoplasmic reticulum and transported as vesicles to the cell membrane.
What model was proposed by Gorter and Grendel in 1925?
Phospholipids can form bilayers because of their amphiphilic characteristic. The structure of the phospholipid molecule generally consists of two hydrophobic fatty acid "tails" and a hydrophilic "head" consisting of a phosphate group.
Fluidity
Phospholipids can move within the bilayer, making the membrane flexible or "fluid."*.
Why do phospholipids form bilayers in water?
Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules.
Images
Pictures or diagrams developed in an effort to represent something
Hydrophilic
Polar or ionic molecules that are capable of forming bonds with water molecules; Attract water molecules.
Polymerization
Polymerization is the process in which relatively small molecules, called monomers, combine chemically to produce a large chainlike molecule, called a polymer. Polymerization is an anabolic reaction, in which complex molecules form from simpler molecules by condensation reactions.
Channels
Pores through a protein with very narrow diameter. The diameter and chemical properties of the proteins ensure that only one type of particle can pass through. For example, a channel could move sodium ions or potassium ions, but not both.
History of Vitalism
Prior to 250 B.C., the Greek physician Erasistratus developed the idea of a "vital pneuma" carried by the arteries to the brain, where it was transformed into "animal spirits" responsible for movement and sensation. In the 2nd century, the physician Galen argued that pulmonary (lung) veins carries air to the heart where it was converted to vital spirits that was then sent to the rest of the body. 1500 years later the physician William Harvey did experiments that overthrew Galen's ideas, and showed that blood, not air circulates through the body. He still maintained blood to be a spiritual fluid, as he was unable to provide a mechanical explanation for body heat or energy. Throughout the nineteenth century, organic molecules (those made of carbon) became of great interest to chemists and the field of organic chemistry took off. Most chemists believed organic compounds could only be produced by living organisms, as a by product of the vital forces.
Urea
Produced in the liver. Waste product of protein digestion. Transported in the blood to the kidneys where it is filtered out as a component of urine.
Enzyme Proteins
Promote chemical reactions that synthesize or break apart biological molecules. Can be either integral or peripherial.
Evolution of Cells
Protocells, Prokaryotes, Eukaryotes
Sodium-Potassium Pump
Pump protein example Notice in this picture, both Na and K are moving against their concentration gradients (from low to high), which requires energy in the form of ATP.
How does RNA differ from DNA?
RNA contains the sugar ribose, while DNA contains the slightly different sugar deoxyribose RNA has the base uracil while DNA contains thymine. Unlike DNA, most RNA molecules are single-stranded and can adopt very complex three-dimensional structures.
Aristotle Historical Thinking About Spontaneous Generation
Read from the slideshow. Ancient Greek philosopher. Aristotle (384-322 BC) thought there were four elements and a fifth essence called "ether" that occurred only beyond the moon, in the heavens. He thought that the properties of living organisms were due to the mixture of these elements in each part of the body, plus an animating force he called "pneuma." (air)
Paracelsus Historical Thinking About Spontaneous Generation
Read from the slideshow. European chemist and physician. Paracelus (1493-1541) is considered to be the Founder of "toxicology" (science of poisons) and insisted the science be based on an observation of nature rather than relying on ancient texts.
Roles of Membrane Bound Proteins
Receptor Proteins Enzyme Proteins Adhesion Proteins Recognition Proteins Channel Proteins Pump Proteins
Major Histocompatibility Complex (MHC) Proteins
Recognition Protein example. These are proteins on the surface of cells that belong to a particular individual. These MHC proteins interact with immune system cells to identify which cells belong to body and which cells are foreign.
Summarize the Redi Experiment
Redi placed meat three different jars. One jar was left open; the other two were covered. Later, the open jar contained maggots, whereas the covered jars contained no maggots. He did note that maggots were found on the exterior surface of the cloth that covered the jar (attracted to the smell). Redi successfully demonstrated that the maggots came from fly eggs and were not spontaneously generated.
Osmosis in Plants
Root cells have a high concentration of solutes (are hypertonic) relative to the water in the soil. Since water moves from hypotonic to hypertonic solutions, water moves from the soil into the roots via osmosis. Plants have a high concentrations of solutes (hypertonic) in the phloem at the source. Since water moves from hypotonic to hypertonic solution, water will leave the xylem and enter the phloem osmosis. The resulting raised hydrostatic pressure causes the contents of the phloem to flow toward sinks.
Give the Surface Area, Volume and Surface Area:Volume Ratio for the following: 2 cm cube
SA - 24 cm^2 V - 8 cm^3 SA:V - 3:1
Give the Surface Area, Volume and Surface Area:Volume Ratio for the following: 3 cm cube
SA - 54 cm^2 V - 27 cm^3 SA:V - 2:1
Give the Surface Area, Volume and Surface Area:Volume Ratio for the following: 1 cm cube
SA - 6 cm^2 V - 1 cm^3 SA:V - 6:1
When placed in a hypotonic solution, samples will
Samples will gain mass when placed in a hypotonic solution (as water moves into the sample). Size increase.
When placed in a hypertonic solution, samples will
Samples will lose mass when placed in a hypertonic solution (as water moves out of the sample). Size decrease.
Recognition Proteins
Serve as identification tags on the surface of a cell. Often times these are glycoprotiens (proteins with an attached sugar molecule) Can be integral or peripheral.
Pump Proteins
Serve as pores/tunnels for large or hydrophilic molecules to be actively (energy required) transported into/out of the membrane All are integral
Channel Proteins
Serve as pores/tunnels for large or hydrophilic molecules to be passively (no energy required) transported into/out of the membrane All are integral
How are fatty acids similar to phospholipids?
Similar to phospholipids, fatty acids have a hydrophobic tail and hydrophilic head, and can thus form the same types of structures, such as vesicles, micelles, and bilayers.
How can particles move across membranes?
Simple diffusion, facilitated diffusion, osmosis, and active transport.
Explain why cells are often limited in size by the SA:V ratio. (Small cells)
Small cell has larger SA:V ratio. Small volume requires fewer metabolic nutrients and waste to be transported through the cell membrane. Relatively more cell membrane for transporting materials into/out of the cell. Molecules have shorter distance to diffuse within the cell.
Examples of Facilitated Diffusion: Sodium (Na+) and Potassium (K+) Channels
Sodium (Na+) and potassium (K+) channels in neuron cell membranes are used for facilitate diffusion during transmission of an action potential.
Active Transport Examples
Sodium Potassium Pump In plants: Proton Pump in Cellular Respiration and Photosynthesis, Auxin Efflux Pumps, Roots, Phloem Sieve Tubes. In animals: kidney, small intestine
Summarize the Spallanzani Experiment
Spallanzani put broth in a flask, sealed the flask so that way no air could get in, and boiled it. No organisms grew in that flask. This suggested that microbes were introduced into these flasks from the air. In response to Spallanzani's findings, others argued that life originates from a "life force" that was destroyed during Spallanzani's extended boiling.
Integral Proteins
Span the entire membrane (transmembrane proteins are examples) Permanently attached to the cell membrane.
Outline the activities occurring at the surface of the cell.
Surface Area A cell's surface area is determined by its cell membrane. The cell membrane regulates transport of molecules into and out of the cell. Oxygen gas and nutrient molecules must be absorbed and waste products must be eliminated through the cell membrane.
What is membrane fluidity affected by?
Temperature, Fatty Acid Length, Fatty Acid saturation, presence of cholesterol
Outline properties of RNA that would have allowed it play a role in the origin of cells
The "RNA World" hypothesis* proposes that RNA was the first genetic material. RNA has properties that would allow it to function in this manner: RNA can self-replicate, the third step of the Oparin-Haldane hypothesis. [reference] RNA can serve as a genetic code for protein synthesis between generations. RNA can act as a catalyst, speeding up the polymerization of amino acids to form proteins.
Examples of Facilitated Diffusion: CFTR Channel
The CFTR Channel moves chloride ions out of the cell. People with cystic fibrosis have a mutation that causes the CFTR channel to have the wrong shape and as a result the channel can not move the chloride ions. The ions build up in the cell. The consequences are huge.
RNA World Hypothesis
The RNA World Hypothesis is the idea that before living cells, the DNA genetic code, and the gene/protein cycle ever existed, chains of a chemical called RNA were forming naturally. Once formed, some of these RNA chains were able to function as enzymes, and were even able to evolve by making copies of themselves with slight, accidental modifications.
What does surface area dictate?
The amount of exchange across the cell membrane. The more surface area, the more exchange of nutrients and gases into the cell and wastes out of the cell through the cell membrane.
What does volume dictate?
The amount of materials that are needed or produced in the cytoplasm. The more volume, the more nutrients and gases that are needed inside the cell for metabolic reactions. The more volume, the more waste that is produced that must leave the cell.
Volume
The amount of space a 3D shape takes up. The volume of a cube is equal to the side length cubed. a^3
The Cell Theory
The cell is the basic unit of life. All living things are composed of cells. Cells come from preexisting cells.
Osmolarity
The concentration of solutes in a solution. The number of particles of solute per liter of solution. = moles of solute/liters of solvent
Diffusion of CO2 and O2 into and out of eye cornea cells. Information, how it can happen, and draw picture.
The cornea is the transparent front part of the eye that covers the iris and pupil. Because the cornea must be transparent (so light can pass through), the cornea does not have blood vessels. But, the cells of the cornea are alive and must receive oxygen and get rid of carbon dioxide waste. How can this happen? The cornea receives nutrients via diffusion from the tear fluid through the outside surface and the vitreous humour (eyeball juice) through the
ATP (adenosine triphosphate)
The energy molecule.
What did Miller and Urey test?
The first step of the Oparin-Haldane hypothesis; whether simple organic molecules can form from inorganic compounds.
Vitalism
The idea that living organisms possess a "life force" distinct from purely chemical or physical elements.
Surface Area
The total of all the faces that make up a 3D shape. Since cubes have 6 sides, the surface area is equal to six times the side length squared. 6a^2
Passive
The transport method does not require energy. Moves from high concentration to low concentration.
Mathematical Models
The use of mathematical language to describe the behavior of a system.
Davson and Danielli
The membrane includes globular protein molecules attached to each side of the lipid bilayer. Using the newly invented electron microscope that allowed for greater magnification of the membrane, Davson and Danielli observed that protein was on the outer edge because proteins show up dark under the electron microscope- with lipids showing up clear. Since they saw parallel dark lines with a clear region in between, Davson and Danielli deduced that the cell membrane had a phospholipid bilayer (the clear part) that was "sandwiched" between two layers of protein (the dark lines). Although structurally incorrect, the Davson-Danielli model increased understanding of cell membranes by including proteins in biological membranes.
Singer and Nicolson
The membrane is a fluid bilayer of lipids with embedded proteins. Membrane proteins are not uniform in shape and some are hydrophobic. Such proteins would not form a continuous layer on the outer surface of the membrane. Used electron microscope and freeze etching to prove Davson and Danielli wrong. OBSERVATION: evidence mounted which undermined the Davson-Danielli model of membrane structure, S. Jonathan Singer and Garth Nicolson (1972) proposed the fluid mosaic model of the cell membrane. DEDUCTION: the cell membrane is a mosaic of proteins embedded in the membrane, and the membrane being a fluid bilayer of lipids. The lipid bilayer suggestion agrees with previous models but the Singer-Nicolson model includes proteins as globular structures that can embedded in the layer rather than forming sheets on the membrane surface.
Views on Vitalism after Friedrich's Artificial Urea Synthesis?
The millennium-old belief of vitalism could not be overturned by just one experiment. Critics would point out that Wöhler's synthesis of urea was only a byproduct of the life process, as urea wasn't necessary for life. In the later half of the nineteenth century, organic chemistry became a scientific discipline and scientists started to doubt vitalism as a scientific theory. Vitalism explained everything without evidence and denied the acceptance of new evidence. Essentially it was decided that vitalism just wasn't science.
Active Transport
The movement of substances from areas low concentration to areas of high concentration through protein pumps. Against the gradient. Requires energy to happen (typically in the form of ATP).
Osmosis
The movement of water by diffusion across a membrane. Passive; doesn't require energy. Depends on the amount of solutes in solutions in relation to each other.
Diffusion
The net movement of molecules from areas of higher concentration to areas of lower concentration. Passive; requires no energy.
How Is the Structure of a Membrane Related to Its Function?
The phospholipid bilayer Is the fluid portion of the membrane A mosaic of proteins is embedded in the membrane Membranes are dynamic, ever-changing structuresHow Is the Structure of a Membrane Related to Its Function?
What is membrane fluidity affected by?: Presence of cholesterol.
The presence of cholesterol affects fluidity depending on the temperature. High temperature: cholesterol decreases fluidity. Low temperature: cholesterol increases fluidity.
What are processes in living organisms governed by?
The same chemical and physical forces as in non-living matter.
Spontaneous Generation
The theory, now discredited, that living organisms can routinely emerge from nonliving matter independently of other living matter.
Explain why phospholipids form bilayers in water, with reference to hydrophilic phosphate heads and two hydrophobic hydrocarbon tails.
There is water on either side of the cell membrane. Inside = cytoplasm Outside = extracellular fluid Phospholipids will arrange themselves as a bilayer so that the hydrophilic head associates with water inside and outside of the membrane and the hydrophobic tails face each other, within the membrane, away from the water.
When placed in an isotonic solution...
There will be zero change in mass when the sample is placed in an isotonic solution. Size stays the same.
Even though scientists cannot say for sure how life on Earth arose, what can they do?
They can formulate and test hypotheses about natural processes that could account for various intermediate steps.
A 0.9% NaCl solution is isotonic to red blood cells. Which of these describes the results if red blood cells are placed into a 9% solution of NaCl?
They will shrink.
What does it mean when the SA:V ratio becomes to small?
This means that the amount of surface area for exchange of materials through the cell (either nutrients in or waste out) is too little for the metabolic demands of the volume and the cell will not be able to function properly.
What must be done to tissues or organs to be used in medical procedures?
Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis.
Phospholipid Tail Structure
Two fatty acids (chains of hydrogen and carbon atoms, termed "hydrocarbon chain"). The fatty acid tails can be Phospholipid saturated, monounsaturated or polyunsaturated.
What is membrane fluidity affected by? Fatty Acid Saturation
Unsaturated fatty acids have one or more double bonds in the fatty acid tails. Double bonds lead to a "bend", pushing the adjacent phospholipids further apart. The increased spacing increases fluidity.
Active Transport Examples: Sodium Potassium Pump in Neurons
Use active transport to maintain the resting membrane potential in neurons. Without it you would die.
Outline the activities occurring in the volume of the cell.
Volume The internal regions of the cell are what constitute the cell's volume. Many metabolic reactions occur within the cell's volume. The metabolic reactions require gases and chemical nutrients and produce waste.
fatty acids
Were likely the components of early membranes.
Why do biologists now universally accept that cells only come from preexisting cells?
With improved observational tools and a focus on controlled experiments, we now know that cells only come from existing cells. Early Italian Compound Microscope (circa late 1600s) to the Early Ross Compound Microscope (circa 1831)
Oparin-Haldane hypothesis
a four step process that shows how life could arise on Earth
Concentration gradient
a gradient resulting from an unequal distribution of ions across the cell membrane.
The concentration of solutes in a red blood cell is about 2%. Sucrose cannot pass through the membrane, but water and urea can. Osmosis would cause red blood cells to shrink the most when immersed in which of the following solutions?
a hypertonic sucrose solution
Hypotonic
a less concentrated solution relative to another fluid.
Phospholipids
a lipid consisting of a glycerol bound to two fatty acids and a phosphate group.
Cholesterol
a lipid that prevents the membrane from becoming too and also prevents it from crystalizing.
Fluid mosaic model
a model conceived by S.J. Singer and Garth Nicolson in 1972 to describe the observed structural features of biological membranes.
Hypertonic
a more concentrated solution relative to another fluid.
Genetic code
a nearly universal sequence of nucleotides in DNA that determines the specific amino acid sequence in the synthesis of proteins.
Endosymbiotic theory
a theory that some eukaryotic organelles, such as mitochondria and chloroplasts, originated as free-living prokaryotes that invaded primitive eukaryotic cells.
Franceso Redi
disproved spontaneous generation. maggots/red meat. used scientific method
Bilayer
double layer
Protocells
droplets with membranes that maintained an internal chemistry different from that of their surroundings
If a cell has a lower solute concentration than the solution, the solution is __________ and the cell is __________. Net water movement?
hypertonic hypotonic Since water moves from hypotonic to hypertonic solutions NET water movement will be out of the cell and the cell will shrink. If too much water leaves the cell, it will die.A 0.9% NaCl solution is isotonic to red blood cells. Which of these describes the results if red blood cells are placed into a 9% solution of NaCl?
RNA world hypothesis
hypothesis that RNA was the first nucleic acid to evolve and that early life was based on RNA, rather than DNA or protein
If a cell has a higher solute concentration than the solution, the solution is __________ and the cell is __________. Net water movement?
hypotonic hypertonic Since water moves from hypotonic to hypertonic solutions NET water movement will be into the cell and the cell will swell. If too much water moves into the cell, it will burst.
Davson-Danielli model
model of the cell membrane in which the phospholipid bilayer is between two layers of protein.
Amphipathic
molecule that has hydrophobic and hydrophilic regions.
Hydrophilic
molecules that are attracted to water.
Hydrophobic
molecules that are not attracted to water but are attracted to each other.
Active transport
movement of substances across membranes using energy in the form of ATP.
Electron carriers
proteins arranged in chains on the membrane to allow the transfer of electrons from one carrier to another.
Integral proteins
proteins embedded in the phospholipid bilayer.
Transport pumps
proteins in the plasma membrane that release energy and use it to move substances across the membrane.
Hormone-binding sites
proteins on the outside of the membrane that allow specific hormones to bind.
Peripheral proteins
proteins on the surface of the plasma membrane.
Glycoproteins
proteins that contain oligosaccharide chains.
Fluidity
refers to the viscosity of a lipid bilayer of the membrane that allows it to change shape.
For facilitated diffusion, phospholipid bilayer must be...
studded with channel proteins to allow facilitated diffusion to occur.
Sterilization
technique used for the elimination of microbiological organisms to achieve a sterile microbial environment.
Vitalism
the belief in a life force outside the jurisdiction of physical and chemical laws
Endocytosis
the process in which the cell takes in materials from the outside by infolding of the membrane to form a vesicle.
Permeability
the rate of passive diffusion of molecules through the membrane, which depends on the electric charge, size, and polarity of the molecule.
Phospholipid bilayer
two layers of phospholipids arranged so that their hydrophobic tails are projecting inwards while their polar head groups are on the outside surfaces.
Secretion
when material is released from a cell.
