Chap 7 For Bio Final
PART A - Understanding the parts of the graph Which variable is the independent variable--the variable that was controlled by the researchers? Is the independent variable on the x-axis or the y-axis? -
incubation time; on the x-axis
PART E - Reading the graph What concentration of radioactive glucose did the researchers find in the red blood cells of a 15-day-old guinea pig after an incubation time of 30 minutes? -
85 mM
Why is a transport protein needed to move water molecules rapidly and in large quantities across a membrane?
A transport protein is needed to move water molecules rapidly and in large quantities across a membrane because since water is a hydrophilic molecule, it will take much longer to permeate the lipid bilayer, relative to hydrophobic molecules such as CO2. Water is a polar molecule, so it cannot pass very rapidly through the hydrophobic region in the middle of a phospholipid bilayer.
7.5 -Which process yields more ATP, fermentation or anaerobic respiration piration? Explain. -
Anaerobic respiration process yields more ATP because the 2 ATP produced by substrate-level phosphorylation is the total energy yield of fermentation.
What is the research method for freeze-freeze fracture?
Application: A cell membrane can be split into its two layers, revealing the structure of the membrane's interior. Technique: A cell is frozen and fractured with a knife. The fracture plane often follows the hydrophobic interior of a membrane, splitting the phospholipid bilayer into two separated layers. Each membrane protein goes wholly with one of the layers. Results: SEM's show membrane proteins (the "bumps") in the two layers, demonstrating that proteins are embedded in the phospholipid bilayer.
What does it mean to accept or reject a model that is proposed?
Because models are hypotheses, replacing one model of membrane structure with another does not imply that the original model was worthless. The acceptance or rejection of a model depends on how well it fits observations and explains experimental results. New findings may make a model obsolete; even then, it may not be totally scrapped, but revised to incorporate the new observations. The fluid mosaic model is continually being refined. For example, group of proteins are often found associated in long-lasting, specialized patches, where they carry out common functions. The lipids themselves appear to form defined regions as well. Also, the membrane may be much more packed with proteins than imagined in the classic fluid mosaic model-compare the updated model with the original model (7.5 vs 7.3).
PART F - Interpreting the graph Identify the trend common to both the 15-day-old and 1-month-old guinea pigs' red blood cells. -
Both experienced the most rapid uptake of glucose at the beginning of the experiment.
In absence of O2 as in question 1, what do you think would happen if you decreased the pH of the intermembrane space of the mitochondrion? Explain your answer. -
Decreasing pH would mean increasing of H+. This would establish a proton gradient even without the function of the electron transport chain, and we would expect ATP synthase to function and synthesize ATP.
The soil immediately around hot springs is much warmer than that in neighboring regions. Two closely related species of native grasses are found, one in the warmer region and one in the cooler region. if you analyzed their membrane lipid compositions, what would you expect to find?
I would expect them to have unsaturated fatty acids(double bonds) which allow for kinks - in their membrane lipid compositions. The grasses living in the cooler region would be expected to have more unsaturated fatty acids in their membranes because those fatty acids remain fluid at lower temperatures. The grasses living immediately adjacent to the hotspring would be expected to have more saturated fatty acids, which would allow the fatty acids to "stack" more closely, making the membranes less fluid and therefore helping them to stay intact at higher temperatures. (Cholesterol could not be used to moderate the effects of temperature on membrane fluidity because it is not found within plant cell membranes. - ( Haha, wow such an obvious mistake on my part, only animals contain cholesterol, always learning, excellent.
What is intercellular joining? (Figure 7.10e)
Membrane proteins of adjacent cells may hook up together in various kinds of junctions such as gap junctions (I remember this) or tight junctions. This type of binding is more long-lasting than that shown in (d).
What are the characteristics of biological membranes?
Membranes are not static sheets of molecules locked rigidly in place. A membrane is held together primarily by hydrophobic interactions, which are much weaker than covalent bonds. Most of the lipids and some of the proteins can shift laterally - that is, in the plane of membrane, like partygoers elbowing their way through a crowded room. It is quite rare, however, for a molecule to flip-flop transversely across the membrane, switching from one phospholipid layer to the other; to do so, the hydrophilic part of the molecule must cross the hydrophobic interior of the membrane.
During step 6 in figure 7.9, which molecule acts as the oxidizing agent? The reducing agent? -
NAD+ acts as oxidizing agent and 3 phosphate, which thus acts as the reducing agent.
How are membrane proteins held in place to the plasma membrane?
On the cytoplasmic side of the plasma membrane, some membrane proteins are held in place by attachment to the cytoskeleton. And on the extracellular side, certain membrane proteins are attached to the fibers of the extracellular matrix (integrins are one type of integral protein). These attachments combine to give animal cells a stronger framework than the plasma membrane alone could provide.
Membranes must be fluid to function properly (as you learned in concept 5.1) how does the operation of the electron transport chain support that assertion? -
One of the components of the electron transport chain, ubiquinone, must be able to diffuse within the membrane. It could not do so if the membrane were locked rigidly into place.
How does the hydrophobic interior of the membrane impede the direct passage of ions and polar molecules, which are hydrophilic, through the membrane.
Polar molecules such as glucose and other sugars pass only slowly through a lipid bilayer, and even water, an extremely small polar molecule, does not cross very rapidly. A charged atom or molecule and its surrounding shell of water find the hydrophobic interior of the membrane even more difficult to penetrate. Furthermore, the lipid bilayer is even more difficult to penetrate. Furthermore, the lipid bilayer is only one aspect of the gate-keeper system responsible for the selective permeability of a cell. Proteins built into the membrane play key roles in regulating transport.
consider the NADH formed during glycolysis. What is the final receptor for it's electrons during fermentation? What is the final acceptor for it's electrons during aerobic respiration? -
Pyruvate is the final receptor during lactic acid fermentation, and acetadehyde during alcohol fermentation. Oxygen during aerobic respiration.
How do the transport proteins called "channel proteins" function?
Some transport proteins, called channel proteins, function by having a hydrophilic channel that certain molecules or atomic ions use as a tunnel through the membrane. For example, the passage of water molecules through the membrane in certain cells is greatly facilitated by channel proteins known as aquaporins.
Where does the word "mosaic" fit into the aspect of the fluid mosaic model?
Somewhat like a tile mosaic, a membrane is a collage of different proteins, often clustered together in groups, embedded in the fluid matrix of the lipid bilayer. More than 50 kinds of proteins have been found so far in the plasma membrane of red blood cells for example. Phospholipids form the main fabric of the membrane, but proteins determine most of the membrane's functions. Different types of cells contain different sets of membrane proteins, and the various membranes within each cell have a unique collection of proteins.
How do the molecules switch from one phospholipid layer to the other?
The lateral movement of phospholipids within the membrane is rapid. Adjacent phospholipids switch positions about 10^7 times per second. A phospholipid can travel the length of many bacterial cells in 1 second. Proteins are much larger than lipids and move more slowly, but some membrane proteins do drift. And some membrane proteins seem to move in a highly directed manner, perhaps driven along cytoskeletal fibers by motor proteins connected to the membrane protein's cytoplasmic regions. However, many other membrane proteins seem to be held immobile by their attachment to the cytoskeleton or to the extracellular matrix.
What is the most abundant lipid in most membranes?
The most abundant lipid in most membranes are phospholipids. The ability of phospholipids to form membranes is inherent in their molecular structure. A phospholipid is an amphipathic molecule, meaning that it has both a hydrophilic region and a hydrophobic region.
7.3 -What molecular products indicate the complete oxidation of glucose during cellular respiration. -
The release of six molecules of CO2 represents the complete oxidation of glucose.
How do integral proteins pump substances across the membrane?
They can do this because they can hydrolyze ATP as an energy source.
What are some examples of variations in the cell membrane lipid compositions of species?
Variations in the cell membrane lipid compositions of many species appear to be evolutionary adaptations that maintain the appropriate membrane fluidity under specific environmental conditions. For instance, fishes that live in extreme cold have membranes with a high proportion of unsaturated hydrocarbon tails, enabling their membranes to remain fluid. At the other extreme, some bacteria and archaea thrive at temperatures greater than 90 C (194 F) in thermal hot springs and geysers. Their membranes include unusual lipids that may prevent excessive fluidity at such high temperatures.
Do the carbohydrates on the extracellular side of the plasma membrane vary from species to species?
Yes the carbohydrates on the extracellular side of the plasma membrane vary from species to species, among individuals of the same species, and even from one cell type to another in a single individual (Jesus christ). The diversity of the molecules and their location on the cell's surface enable membrane carbohydrates to function as markers that distinguish one cell from another. For example, the four human blood types designated A, B, AB, and O reflect variation in the carbohydrate part of glycoproteins on the surface of red blood cells.
What are carrier proteins and what is their function?
Carrier proteins are transport proteins that hold onto their passengers and change shape in a way that shuttles them across the membrane. A transport protein is specific for the substance it translocates (moves), allowing only a certain substance (or a small group of related substances) to cross the membrane. For example, a specific carrier protein in the plasma membrane of red blood cells transports glucose across the membrane 50,000 times faster than glucose can pass through on its own. (Wow... amazingly fast..). This "glucose transporter" is so selective that it even rejects fructose, a structural isomer of glucose. ( I wonder if we could manipulate this glucose transporter in order to accept fructose. I wonder what the consequences would be.) Would it be possible to engineer the glucose transporter to perhaps transport glucose across the membrane 100,000 or 1,000,000 times faster than glucose can pass on its own, in order to enhance the speed and power of our Olympic athletes.
Are cell membranes permeable to polar molecules and ions?
Cell membranes ARE permeable to specific ions and a variety of polar molecules. These hydrophilic substances can avoid contact with the lipid bilayer by passing through transport proteins that span the membrane.
A red blood cell has been placed into three different solutions. One solution is isotonic to the cell, one solution is hypotonic to the cell, and one solution is hypertonic to the cell. Determine which type of solution is in each beaker based on the cell's reaction. -
ISOTONIC: normal HYPOTONIC: slightly diluted (almost normal) HYPERTONIC: concentrated (deformed) (For a cell in an isotonic solution, water flows into the cell to the same extent that it flows out of the cell. If a cell is in a hypotonic solution, water flows into the cell, which causes it to swell and potentially burst. For a cell in a hypertonic solution, water flows out of the cell, which causes it to shrink.)
Why do enzymes sometimes work in teams? (Figure 7.10b - Some functions of membrane proteins)
In some cases, several enzymes in a membrane are organized as a team that carries out sequential steps of a metabolic pathway.
What effect would an absence of O2 have on the process shown in figure 7.14 -
Oxidation phosphorylation would entirely stop result in no ATP production by this process. If there is no O2 to pull electron down to electron chain, H+ would not be pumped into the mitochondrion inter-membrane space and chemiosmosis would not occur.
Is glucose uptake into cells affected by age? Glucose, an important energy source for animals, is transported into cells by facilitated diffusion using protein carriers. In this exercise, you will interpret a graph from an experiment in which researchers incubated guinea pig red blood cells in a 300 mM (millimolar) radioactive glucose solution at pH 7.4 at 25°C. Every 10 or 15 minutes, they removed a sample of cells from the solution and measured the concentration of radioactive glucose inside those cells. Cells came from either a 15-day-old guinea pig or a 1-month-old guinea pig. The graph at left shows the data from the experiment. -
Part A - Part H
What are peripheral proteins?
Peripheral proteins lie on the membrane of cells. They are not embedded in the lipid bilayer at all; they are appendages loosely bound to the surface of the membrane, often to exposed parts of integral proteins.
A semipermeable membrane is placed between the following solutions. Which solution will decrease in volume? -
Solution A: 1.4% (m/v) starch (The water molecules actually move in both directions, but they move to a greater extent toward Solution B because it has a higher solute concentration than Solution A. The net movement of water molecules causes Solution A to decrease in volume and Solution B to increase in volume)
How does membrane sidedness arise?
The asymmetrical arrangement of proteins, lipids and their associated carbohydrates in the plasma membrane is determined as the membrane is being built by the ER and Golgi apparatus.
How is the biological membrane an example of a supramolecular structure?
The biological membrane is an exquisite example of a supramolecular structure (many molecules ordered into a higher level of organization) with emergent properties beyond those individual molecules One of the most important of those emergent properties is the ability to regulate transport across cellular boundaries, a function essential to the cell's existence. The fluid mosiac model helps explain how membranes regulate the cell's molecular traffic.
A glucose-fed yeast cell is moved from an aerobic environment to an anaerobic one. How would its rate of glucose consumption change if ATP were to be generated at the same rate? -
The cell would have to consume glucose at a rate about 16 times the consumption rate in the aerobic environment.
compare the structure of a fat with that of a carbohydrate. What features of their structures make fat a much better fuel? -
The fat is much more reduced, and it has lots of ---Ch2--- bonds in with electrons are equally shared. Carbohydrate bonds are already somewhat oxidized,, as some of them are bound to oxygen.
7.4 -Briefly explain the mechanism by which ATP synthase produces ATP. List three location in which ATP synthases are found. -
The flow of H+ through the ATP synthase complex causes the rotor and attached rod to rotate, exposing catalytic sites in the knob portion that produce ATP from ADP and Pi. ATP synthase are found in the inner mitochondrial membrane, the plasma membrane of prokaryotes, and membrane within chloroplast.
Aquaporins exclude passage of hydronium ions. Recent research on fat metabolism has shown that some aquaporins allow passage of glycerol, a three carbon alcohol, as well as H2O. Since H3O+ is much closer in size to water than is glycerol, what do you suppose is the basis of this selectivity?
The hydronium ion is charged, while glycerol is not. Charge is probably more significant than size as a basis for exclusion by the aquaporin channel. (Interesting how they said probably, it means this is not conclusive. But why would charge be more significant than size? What is so special about charge that makes it more difficult for a hydronium to pass through aquaporins that allow the passage of water?)
PART H- Evaluating hypotheses Which of the following hypotheses is a reasonable explanation for the data represented in the graph? -
The red blood cells of older guinea pigs have fewer glucose transporter proteins than the red blood cells of younger guinea pigs.
PART D What do the blue dots represent? -
the concentration of radioactive glucose found in a 1-month-old guinea pig's red blood cells after different incubation times
Why are proteins on the surface of a cell important in the medical field?
Proteins on the surface of a cell are important in the medical field because some proteins can help outside agents invade the cell. For example, cell-surface proteins help the human immunodeficiency virus (HIV) infect immune system cells, leading to the acquired immune deficiency syndrome (AIDS). Learning about the proteins that HIV binds to on immune cells has been central to developing a treatment for HIV infection.
A semipermeable membrane is placed between the following solutions. Which solution will increase in volume? -
Solution D: 12.4% (m/v) NaCl (The water molecules actually move in both directions, but they move to a greater extent toward Solution D because it has a higher solute concentration than Solution C. This net movement of water molecules causes Solution D to increase in volume and Solution C to decrease in volume)
How do glycoproteins serve as ID tags in cell to cell recognition? (Figure 7.10d)
Some glycoproteins serve as ID tags that are specifically recognized by membrane proteins of other cells. This type of cell to cell binding is usually short-lived relative to what is in Fig 7.10e.
7.6 - Describe how the catabolic pathways of glycolysis and the critic acid cycle intersect with anabolic pathways in the metabolism. -
The ATP produced by catabolic pathways is used to drive anabolic pathways. Also, many of the intermediates of glycolysis and the critic acid cycle are used in the biosynthesis of a cell's molecules.
under what circumstances might your body synthesize fat molecules? -
When you eat food more than you are suppose to, your body stores them in fat for later use.
Potato slices that are immersed in fresh water for several hours become stiff and hard. Similar slices left in a 0.2 M salt solution become limp and soft. From this we can deduce that the cells of the potato slices are -
hypertonic to fresh water but hypotonic to the salt solution.
Under what circumstances does membrane transport always require energy? -
whenever a solute needs to be moved from low concentration to high concentration through a phospholipid bilayer membrane
What does the term "glyco" refer to?
It refers to the presence of carbohydrates.
Because ions carry a charge (positive or negative), their transport across a membrane is governed not only by concentration gradients across the membrane but also by differences in charge across the membrane (also referred to as membrane potential). Together, the concentration (chemical) gradient and the charge difference (electrical gradient) across the plasma membrane make up the electrochemical gradient. Consider the plasma membrane of an animal cell that contains a sodium-potassium pump as well as two non-gated (always open) ion channels: a Na+ channel and a K+ channel. The effect of the sodium-potassium pump on the concentrations of Na+ and K+ as well as the distribution of charge across the plasma membrane is indicated in the figure below. Which of the following statements correctly describe(s) the driving forces for diffusion of Na+ and K+ ions through their respective channels? Select all that apply. -
-The diffusion of Na+ ions into the cell is facilitated by the Na+ concentration gradient across the plasma membrane -The diffusion of K+ ions out of the cell is impeded by the electrical gradient across the plasma membrane. -The electrochemical gradient is larger for Na+ than for K+. (The concentration gradient of Na+ ions across the membrane (higher Na+ concentration outside) facilitates the diffusion of Na+ into the cell. At the same time, the electrical gradient across the membrane (excess positive charge outside) drives Na+ into the cell. The concentration gradient of K+ ions across the membrane (higher K+ concentration inside) facilitates the diffusion of K+ out of the cell. However, the electrical gradient across the membrane (excess positive charge outside) impedes the diffusion of K+ out of the cell. The electrochemical gradient for an ion is the sum of the concentration (chemical) gradient and the electrical gradient (charge difference) across the membrane. For Na+ ions, diffusion through the Na+ channel is driven by both the concentration gradient and the electrical gradient. But for K+ ions, the electrical gradient opposes the concentration gradient. Therefore, the electrochemical gradient for Na+ is greater than the electrochemical gradient for K+.)
Some solutes are able to pass directly through the lipid bilayer of a plasma membrane, whereas other solutes require a transport protein or other mechanism to cross between the inside and the outside of a cell. The fact that the plasma membrane is permeable to some solutes but not others is what is referred to as selective permeability. Which of the following molecules can cross the lipid bilayer of a membrane directly, without a transport protein or other mechanism? Select all that apply. -
-oxygen -water -carbon dioxide -lipids (Some solutes pass readily through the lipid bilayer of a cell membrane, whereas others pass through much more slowly, or not at all. Small nonpolar (hydrophobic) molecules, such as dissolved gases (O2, CO2, N2) and small lipids, can pass directly through the membrane. They do so by interacting directly with the hydrophobic interior of the lipid bilayer. Very small polar molecules such as water and glycerol can pass directly through the membrane, but much more slowly than small nonpolar molecules. The mechanism that permits small polar molecules to cross the hydrophobic interior of the lipid bilayer is not completely understood, but it must involve the molecules squeezing between the hydrophobic tails of the lipids that make up the bilayer. Polar molecules such as glucose and sucrose have very limited permeability. Large molecules such as proteins cannot pass through the lipid bilayer. Ions and charged molecules of any size are essentially impermeable to the lipid bilayer because they are much more soluble in water than in the interior of the membrane.)
All molecules have energy that causes thermal motion. One result of thermal motion is diffusion: the tendency of substances to spread out evenly in the available space. Although the motion of each individual molecule is random, there can be directional motion of an entire population of molecules. Consider a chamber containing two different types of dye molecules, purple and orange. The chamber is divided into two compartments (A and B) by a membrane that is permeable to both types of dye. Initially (left image), the concentration of the orange dye is greater on side A, and the concentration of the purple dye is greater on side B. With time, the dye molecules diffuse to a final, equilibrium state (right image) where they are evenly distributed throughout the chamber. -
1. Orange dye moves independently of purple dye. ALWAYS 2. Concentration gradients exist that drive diffusion of both dyes ONLY BEFORE EQUILIBRIUM 3. There is a net movement of orange dye from side A to side B. ONLY BEFORE EQUILIBRIUM 4. Purple dye moves only from side B to side A. NEVER 5. There is no net movement of purple dye ONLY AT EQUILIBRIUM (Each dye molecule and the water molecules that surround it are in constant motion due to their thermal energy. Any individual molecule's motion is random because of the frequent collisions among all of the molecules. If a concentration gradient exists for a population of molecules, the motion of the individual molecules in that population will result in a net (directional) movement from higher to lower concentration. For example, in the initial condition, there is a concentration gradient for the orange dye. As a result, the orange dye molecules diffuse down the concentration gradient, with net movement from side A to side B. Once diffusion has eliminated the concentration gradient and equilibrium is reached, net movement stops, but the random motion of each molecule continues (as indicated by the red arrows in the image below).)
Describe how signal transduction works. (Figure 7.10c)
A membrane protein (receptor) may have a binding site a specific shape that fits the shape of a chemical messenger, such as a hormone. The external messenger (signaling molecule) may cause the protein to change shape, allowing it to relay the message to the inside of the cell, usually by binding to a cytoplasmic protein.
How do changes in the temperature affect biological membranes?
A membrane remains fluid as temperature decreases until finally the phospholipids settle into a closely packed arrangement and the membrane solidifies, much as bacon grease forms lard when it cools. The temperature at which a membrane solidifies depends on the types of lipids it is made of. The membrane remains fluid to a lower temperature if it is rich in phospholipids with unsaturated hydrocarbon tails (ah that is right!). This is because of kinks in the tails where the double bonds are located. Unsaturated hydrocarbon tails cannot pack together as closely as saturated hydrocarbon tails, and this makes the membrane more fluid.
Part A - Reviewing phospholipid structure -
A phospholipid has a "head" made up of a glycerol molecule attached to a single PHOSPHATE GROUP, which is attached to another small molecule. 2. Phospholipids vary in the small molecules attached to the phosphate group. The phospholipid shown in the figure has a CHOLINE GROUP attached to phosphate. 3. Because the phosphate group and its attachments are either charged or polar, the phospholipid head is HYDROPHILIC, which means it has an affinity for water. 4. A phospholipid also has two "tails" made up of two FATTY ACID molecules, which consist of a carboxyl group with a long hydrocarbon chain attached. 5. Because the C-H bonds in the fatty acid tails are relatively nonpolar, the phospholipid tails are HYDROPHOBIC, which means they are excluded from water.
Compare and contrast aerobic and anaerobic respiration. -
Both respiration includes glycolysis, the critic acid cycle, and oxidative phosphorylation. In aerobic respiration the final electron receptor is molecular oxygen, in anaerobic respiration, the final electron receptor is different substance.
What if the following redox reaction occurred, which compound would be oxidized? which reduced? -
C4H6O5 would be oxidized and NAD+ would be reduced.
Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly? -
CO2
What processes in your cells produced the CO2 that you exhale? -
CO2 is released from the pyruvate that is the end product of glycolysis and CO2 is also released during the critic cycle.
A red blood cell placed in a hypertonic solution will shrink in a process called crenation. A red blood cell placed in a hypotonic solution will swell and potentially burst in a process called hemolysis. To prevent crenation or hemolysis, a cell must be placed in an isotonic solution such as 0.9% (m/v) NaCl or 5.0% (m/v) glucose. This does not mean that a cell has a 5.0% (m/v) glucose concentration; it just means that 5.0% (m/v) glucose will exert the same osmotic pressure as the solution inside the cell, which contains several different solutes. A red blood cell is placed into each of the following solutions. Indicate whether crenation, hemolysis, or neither will occur. Solution A: 3.21% (m/v) NaCl Solution B: 1.65% (m/v) glucose Solution C: distilled H2O Solution D: 6.97% (m/v) glucose Solution E: 5.0% (m/v) glucose and 0.9%(m/v) NaCl -
CRENATION: A, D, and E HEMOLYSIS: B and C NEITHER: (This activity shows why it is very important to use solutions that are isotonic to body fluids in intravenous solutions (IVs). If an IV solution were hypertonic to the body fluids, cells in the body would shrink. If an IV solution were hypotonic to the body fluids, cells in the body would swell)
Give me an example of the steady traffic of small molecules and ions moving across the plasma membrane in both directions.
Consider the chemical exchanges between a muscle cell and the extracellular fluid that bathes it. Sugars, amino acids, and other nutrients enter the cell, and metabolic waste products leave it. The cell takes in O2 for use in cellular respiration and expels CO2. Also, the cell regulates its concentrations of inorganic ions, such as Na+, K+, Ca2+, and CI-, by shuttling them one way or the other across the plasma membrane. In spite of heavy traffic through them, cell membranes are selectively permeable, and substances do not cross the barrier indiscriminately. The cell is able to take up some small molecules and ions and exclude others. Also, substances that move through the membrane do so at different rates.
(Figure 7.11 - Impact) How can we block HIV entry into cells as a treatment for HIV infections?
Despite multiple exposures to HIV, a small number of people do not develop AIDS and show no evidence of HIV-infected cells. Comparing their genes with genes of infected individuals, researchers discovered that resistant individuals have an unusual form of a gene that codes for an immune cell-surface protein called CCR5. Further work showed that HIV binds to a main protein receptor (CD4) on an immune cell, but most types of HIV also need to bind to CCR5 as a "co-receptor" to actually infect the cell. An absence of a CCR5 on the cells of resistant individuals, due to the gene alteration, prevents the virus from entering the cells.
Phospholipids form the main fabric of the plasma membrane. One feature of phospholipids is that when they are placed in an aqueous solution, they will self-assemble into a double layer (bilayer) that resembles the bilayer of the plasma membrane. This self-assembly occurs because phospholipids are hydrophilic at one end (the phospholipid head) and hydrophobic at the other end (the phospholipid tails). -
EF- A) hydrophilic Cytoplasm- B) hydrophilic PM- C) grey on top, yellow on bottom PM- D) grey on bottom, yellow on top outside MP- E) hydrophilic middle MP- F) hydrophobic outside MP- G)hydrophilic (Phospholipids make up the main fabric of the plasma membrane. In the plasma membrane, the phospholipids are found in a bilayer. The hydrophilic heads are exposed to the aqueous environments of the cytoplasm and extracellular fluid, and the hydrophobic tails are sandwiched within, sheltered from these aqueous environments. Other elements of the plasma membrane conform to the hydrophilic and hydrophobic regions established by the phospholipids. For example, membrane proteins have hydrophilic and hydrophobic regions that are found among the hydrophilic and hydrophobic portions of the plasma membrane, respectively. Cholesterol is a hydrophobic molecule and is found among the hydrophobic tails, which you can see in the figure below)
Sort the phrases into the appropriate bins depending on whether they describe exocytosis, endocytosis, or both. -
EXOCYTOSIS: -Increases the surface area of the plasma membrane. -Requires fusion of vesicles with the plasma membrane. -Secretes large molecules out of the cell ENDOCYTOSIS: -Decreases the surface area of the plasma membrane. -Forms vesicles from inward folding of the plasma membrane. BOTH: -Requires cellular energy. -Transported substances physically cross the plasma membrane. (In exocytosis, substances are transported to the plasma membrane in vesicles derived from the endomembrane system. These vesicles fuse with the plasma membrane, releasing the enclosed substances outside the cell. In endocytosis, substances are taken into the cell by folding in of the plasma membrane and pinching off of the membrane to form a vesicle. Notice that in both exocytosis and endocytosis, the transported substances never actually cross the plasma membrane as they leave or enter the cell.)
Figure 7.7 - Inquiry: Do membrane proteins move?
Experiment: Larry Frye and Michael Edidin, at Johns Hopkins University, labeled the plasma membrane proteins of a mouse cell and a human cell with two different markers and fused the cells. Using a microscope, they observed the markers on the hybrid cell. Results: The hybrid cell had mixed proteins after 1 hour - (Is this not cross species genetics - mouses and humans?). Conclusion: The mixing of the mouse and human membrane proteins indicates that at least some membrane proteins move sideways within the plane of the plasma membrane.
What happened when researchers first used electron microscopes to study cells in the 1950's, that revealed two problems with the "sandwich" model that Davson and Danielli proposed?
First inspection of a variety of membranes revealed that membranes with different functions differ in structure and chemical composition. A second, more serious problem became apparent once membrane proteins were better characterized. Unlike proteins dissolved in cytosol, membrane proteins were not very soluble in water because they were amphipathic. If such proteins were layered on the surface of the membrane their hydrophobic parts would be in aqueous surroundings.
If this drug is successful in providing individuals with HIV resistance, what are the social implications? (My thoughts)
First of all it would be amazing for all the individuals in the world, knowing that their partners do not have HIV. I also wonder if HIV will mutate even more and become even more deadly. HIV could learn how to get around the CCR5 disabling and somehow get into the cell through other means. If this drug is successful and HIV is eliminated from the world, I think it would be wonderful for our world, knowing that this deadly virus no longer existed. The discoverers will win a Nobel Prize. Will it make people more promiscuous leading to greater spread of other diseases? I am not sure. I wonder how we can accurately measure how many individuals in the population have a certain disease. I think the only way we can eradicate all these diseases is to tract every single individual at birth with devices that can find their location, the state of the their health, and the total environment. We will need more and more sensors.
What did Hugh Davson and James Danielli suggest in 1935 about biological membranes?
In 1935 these 2 men suggested that the membrane might be coated on both sides with hydrophilic proteins. They proposed a sandwich model: A phospholipid bilayer between two layers of proteins.
In an experiment involving planar bilayers, a solution of table salt (sodium and chloride ions in water) is added on the left side of the membrane while pure water is added on the right side. After 30 minutes the researchers test for the presence of ions on each side of the membrane. The right side tests negative for ions. What can you conclude? -
Ions cannot cross planar bilayers.
What is cell-cell recognition?
It is a cell's ability to distinguish one type of neighboring cell from another, it is crucial to the functioning of an organism. It is important, for example, in the sorting of cells into tissues and organs in an animal embryo. It is also the basis for the rejection of foreign cells by the immune system, an important line of defense in vertebrate animals. (Pathogenic bateria, Graft vs Host Disease [Transplanting a heart from a donor into an individual needs to match on what criteria?], - It was evolved to work for us, but these mechanisms are now preventing us to use embryonic stem cells and other technologies - Fking interesting]. Cells recognize other cells by binding to molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane.
What is selective permeability?
It is a property of biological membranes that allows them to regulate the passage of substances across them. One of the earliest episodes in the evolution may have been the formation of a membrane that enclosed a solution different from the surrounding solution, while still permitting the uptake of nutrients and elimination of waste products. The ability of a cell to discriminate in its chemical exchanges with its environment is fundamental to life, and it is the plasma membrane and its component molecules that make this selectively possible.
What does amphipathic?
It means having both a hydrophilic region and a hydrophobic region.
How long are membrane carbohydrates?
Membrane carbohydrates are usually short, branched chains of fewer than 15 sugar units. Some are covalently bonded to lipids, forming molecules called glycolipids. However, most are covalently bonded to proteins, which are thereby glycoproteins.
Why must membranes be fluid in order to work properly?
Membranes are usually about as fluid as salad oil. When a membrane solidifies, its permeability changes, and enzymatic proteins in the membrane may become inactive if their activity requires them to be able to move within the membrane. However membranes that are too fluid cannot support protein function either. Therefore, extreme environments pose a challenge for life, resulting in evolutionary adaptations that include differences in membrane lipid composition.
How do membrane proteins attach to the cytoskeleton and ECM?
Microfilaments or other elements of the cytoskeleton may be noncovalently bound to membrane proteins, a function that helps maintain cell shape and stabilizes the location of certain membrane proteins. Proteins that can bind to ECM molecules can coordinate extracellular and intracellular changes.
7.1 -Difference between Oxidative Phosphorylation and substrate-level phosphorylation. -
Most of the ATP produced in cellular respiration comes from oxidative phosphorylation, in which the energy released from redox reaction in an electron transport chain is used to produce ATP. IN SUBSTRATE- level Phosphorylation, and enzyme directly transfers a phosphate group to ADP from an intermediate substrate.
Name the molecules that conserve most of the energy from the critic acid cycle's redox reaction. How is this energy converted to a form that can be used to make ATP? -
NADH and FADH2, they will donate electrons to the electron transport chain.
A critical feature of the plasma membrane is that it is selectively permeable. This allows the plasma membrane to regulate transport across cellular boundaries--a function essential to any cell's existence. How does phospholipid structure prevent certain molecules from crossing the plasma membrane freely? -
NONPOLAR: Hydrophobic Can cross easily No transport protein required POLAR: Hydrophilic Have difficulty in crossing the hydrophobic part Transport protein required to cross efficiently IONS: Hydrophilic Have difficulty in crossing the hydrophobic part Transport protein required to cross efficiently (The structure of the plasma membrane makes it selectively permeable, enabling it to regulate the transport of substances into and out of the cell. Small, nonpolar molecules are hydrophobic, so they can easily cross the phospholipid bilayer of the plasma membrane. Polar molecules and ions are hydrophilic, so they cannot very easily cross the hydrophobic portion of the plasma membrane (formed by the phospholipid tails). Water is an unusual molecule because, despite the fact that it is polar, it is small enough to pass directly through the hydrophobic interior of the lipid bilayer, albeit slowly. Polar molecules and ions generally cross the plasma membrane with the help of transport proteins. For example, water crosses the bilayer rapidly via transport proteins called aquaporins)
What type of molecules have an easier time crossing the lipid bilayer, nonpolar or polar molecules?
Nonpolar molecules have an easier time permeating the lipid bilayer because onpolar molecules, such as hydrocarbons, carbon dioxide, and oxygen, are hydrophobic and can therefore dissolve in the lipid bilayer of the membrane and cross it easily, without the aid of membrane proteins.
Two molecules that can cross a lipid bilayer without help from membrane proteins are O2 and CO2. What property allows this to occur?
O2 and CO2 are both nonpolar molecules, therefore they can easily pass through the hydrophobic interior of a membrane. However, the hydrophobic interior of the membrane impedes the direct passage of ions and polar molecules, which are hydrophilic, through the membrane.
The majority of solutes that diffuse across the plasma membrane cannot move directly through the lipid bilayer. The passive movement of such solutes (down their concentration gradients without the input of cellular energy) requires the presence of specific transport proteins, either channels or carrier proteins. Diffusion through a transport protein in the plasma membrane is called facilitated diffusion. Sort the phrases into the appropriate bins depending on whether they are true only for channels, true only for carrier proteins, or true for both channels and carriers. -
ONLY CHANNELS: ~allow water molecules and small ions to flow quickly across the membrane ~Provide a continuous path across the membrane ONLY CARRIERS: ~undergo a change in shape to transport solutes across the membrane ~ transport primarily small polar organic molecules BOTH CHANNELS AND CARRIERS: ~ are integral membrane proteins ~ transport solutes down a concentration gradient or electrochemical gradient ~ provide a hydrophilic path across the membrane (Carrier proteins and channels are both transport proteins involved in facilitated diffusion, the passive transport of solutes across a membrane down their concentration or electrochemical gradient. As integral membrane proteins, both carriers and channels protect polar or charged solutes from coming into contact with the hydrophobic interior of the lipid bilayer. Furthermore, all transport proteins are specific for the solutes they transport, owing to the specificity of the interactions between the solute and the transport protein. Channels are protein-lined pores across the membrane. A channel may be open at all times (non-gated), or may be gated such that the channel opens and closes under specific conditions. Channels transport inorganic ions or water. Diagram showing a channel protein embedded in the membrane that allows yellow balls to travel through a channel from the outside of the cell to the inside. In contrast, carrier proteins do not have a pore. Binding of the transported solute to the carrier protein on one side of the membrane induces a conformational change in the protein that exposes the solute binding site to the opposite side of the membrane, where the solute is released. Carriers transport small polar solutes such as sugars and amino acids.)
Why does knowing about how certain individuals in the population have an unusual form of a gene that codes for an immune cell-surface protein called CCR5, important to us?
Researchers have been searching for drugs to block cell-surface receptors involved in HIV infection. The main receptor protein, CD4, performs many important functions for cells, so interfering with it could cause dangerous side effects. Discovery of the CCR5 co-receptors provided a safer target for development of drugs that mask CCR5 and block HIV entry. One such drug, maraviroc (brand name Selzentry), was approved for treatment of HIV infection in 2007.
When did scientists begin building molecular models of the membrane?
Scientists began building molecular models of the membrane decades before membranes were first seen with the electron microscope (in the 1950's). In 1915, membranes isolated from red blood cells were chemically analyzed and found to be composed of lipids and proteins. Ten years later, two Dutch scientists reasoned that cell membranes must be phospholipid bilayers. Such a double layer of molecules could exist as a stable boundary between two aqueous compartments because the molecular arrangement shelters the hydrophobic tails of the phospholipids from water while exposing the hydrophilic heads to the water.
All cells contain ion pumps that use the energy of ATP hydrolysis to pump ions across the plasma membrane. These pumps create an electrochemical gradient across the plasma membrane that is used to power other processes at the plasma membrane, including some transport processes. In animal cells, the main ion pump is the sodium-potassium pump. Complete the diagram below using the following steps. -
Sodium-Potassium Pump: A) 3 Na+ (up) 2 K+ (down) Outside Cell (B and C): B) [Na+] high [K+] low C) excess + charge Inside Cell (D and E): D) [Na+] low [K+] high E) excess - charge (Active transport by the sodium-potassium pump follows this cycle. 1. Three Na+ ions from the cytosol bind to the pump. 2. The binding of Na+ stimulates the phosphorylation of the pump protein by ATP. 3. Phosphorylation causes a conformational change in the pump that moves the three Na+ ions against their concentration gradient and releases them outside the cell. 4. The release of the Na+ ions permits two K+ ions from outside the cell to bind to the pump, and the phosphate group is released. 5. Release of the phosphate group causes another conformational change in the pump. 6. The conformational change in the pump moves the two K+ ions against their concentration gradient and releases them into the cytosol. A diagram showing six steps of active transport in the sodium-potassium pump. Each numbered step corresponds to the text above. The net result is that the concentration of Na+ is higher outside the cell and the concentration of K+ is higher inside the cell. In addition, one more positive charge has been transported out of the cell than into the cell, leaving the outside of the cell with an excess positive charge and the inside with an excess negative charge. Thus, the sodium-potassium pump creates both chemical gradients and charge differences across the plasma membrane. The function of the sodium-potassium pump in animal cells (and the proton pump in bacteria and plant cells) is essential to many cell functions. It prevents chemical and electrical gradients across the plasma membrane from reaching equilibrium (at which point the cell would be dead) and powers many types of active transport across the plasma membrane)
Name and describe the two ways in which ATP is made during cellular respiration. During what stages in the process does each type occur? -
Substrate- level phosphorylation, which occurs during glycolysis and critic cycle, which involves direct transfer of phosphate group to ADP by an enzyme. Oxidative phosphorylation occurs during the third stage of cellular respiration. In this process the synthesis of ATP from ADP and inorganic phosphate is powered by the redox reaction of the electron transport chain.
What would you predict about CCR5 that would allow HIV to bind to it? How could a drug molecule interfere with this binding?
The CCR5 acts as a helper, like someone on the inside (a bad guy on the inside) that lets the rest of the bad guys in. If we can disable this bad guy it could save many lives and allow individuals to become HIV resistant. I believe a drug molecule could interfere with this binding by either acting as a competitive inhibitor, by blocking the site of connection for the virus. Or it could act as a noncompetitive inhibitor - which is a substance that reduces the activity of the enzyme by binding to the enzyme's (protein) shape so that the active site can no longer effectively catalyze the conversion of a substrate to a product. Need to do additional research to see if my educated guessing stands true. I wonder if this drug has gotten to clinical trials yet.
Give me some more examples of variations in the cell membrane lipid compositions of species.
The ability to change the lipid composition of cell membranes in response to changing temperatures has evolved in organisms that live where temperatures vary. In many plants that tolerate extreme cold, such as winter wheat, the percentage of unsaturated phospholipids increases in autumn, an adjustment that keeps the membranes from solidifying during the winter. Certain bacteria and archaea can also change the proportion of unsaturated phospholipids in their cell membranes, depending on the temperature at which they are growing. Overall natural selection has apparently favored organisms whose mix of membrane lipids ensures an appropriate level of membrane fluidity for their environment.
7.2 -What is the source of energy for the formation of ATP and NADH in glycolysis. -
The oxidation of three-carbon sugar glyceraldehyde 3-phosphate yields energy. In this oxidation, electrons and H+ are transferred to NAD+, forming NADH, and a Phosphate group is attached to the oxidized substrate. ATP id than formed by substrate-level-phosphorylation when this phosphate group is transferred to ADP.
What does the selective permeability of a membrane depend on?
The selective permeability of a membrane depends on both the discriminating barrier of the lipid bilayer and the specific transport proteins built into the membrane. But what establishes the direction of traffic across a membrane? At a given time, what determines whether a particular substance will enter the cell or leave the cell? And what mechanisms actually drive molecules across membranes. (More questions than answers - awesome.)
What is the effect of the steroid cholesterol on membranes?
The steroid cholesterol, which is wedged between phospholipid molecules in the plasma membranes of animal cells, has different effects on membrane fluidity at different temperatures. At relatively high temperatures at 37 C, the body temperature of humans, for example, cholesterol makes the membrane less fluid by restraining phospholipid movement. However, because cholesterol also hinders the close packing of phospholipids, it lowers the temperature required for the membrane to solidify. Thus, cholesterol can be thought of as a "fluidity buffer" for the membrane, resisting changes in membrane fluidity that can be caused by changes in temperature.
What happens when to the transport vesicle that transports glycoproteins, glycolipids, and secretory proteins (purple spheres), when it hits the plasma membrane?
The transport vesicle fuses with the plasma membrane. As the vesicle fuses with the plasma membrane, the outside face of the vesicle becomes continuous with the inside (cytoplasmic) face of the plasma membrane. This releases the secretory proteins from the cell, a process called exocytosis, and positions the carbohydrates of membrane glycoproteins and glycolipids on the outside (extracellular) face of the plasma membrane.
What are the differences between the inside and outside faces of membranes?
The two lipid layers may differ in specific lipid composition, and each protein has directional orientation in the membrane.
PART G What is the main difference between the trends for the 15-day-old and 1-month-old guinea pigs' red blood cells? -
The younger guinea pig's cells took up more glucose than the older guinea pig's cells at all incubation times.
What did S. J. Singer and G. Nicolson propose in 1972 after the "sandwich" model was shown to be wrong thanks to the advent of electron microscopes?
These two men proposed in 1972 that membrane proteins reside in the phospholipid bilayer with their hydrophilic regions protruding. This molecular arrangement would maximize contact of hydrophilic regions of proteins and phospholipids with water in the cytosol and extracellular fluid, while providing their hydrophobic parts with a non-aqueous environment.
What are integral proteins?
They are proteins that exist on membranes. They penetrate the hydrophobic interior of lipid bilayer. The majority are transmembrane proteins, which span the membrane. Other integral proteins extend only partway into the hydrophobic interior. The hydrophobic regions of an integral protein consists of one or more stretches of nonpolar amino acids, usually coiled into alpha helices. The hydrophilic parts of the molecule are exposed to the aqueous solutions on either side of the membrane. Some proteins also have a hydrophilic channel through their center that allows passage of hydrophilic substances (Interesting, I remember this from lecture!)
What is the function of aquaporins?
This channel protein, aquaporin, allows entry of up to 3 billion (3 * 10^9) water molecules per second, passing single file through its central channel which fits ten at a time. (******** thats a lot of molecules - I wonder how much that is in cups?) Without aquaporins, only a tiny fraction of these water molecules would pass through the same area of the cell membrane in a second, so the channel protein brings about a tremendous increase in rate. (Engineering human cells to have no aquaporins, so they would die immediately, due to not have nutrients - evil thought - but holy pits if we remove aquaporins in cancer cells or even pathogenic bacterial cells, perhaps we could slowly kill them overtime, because they don't have enough nutrients.) I believe we could perhaps add more aquaporins to cancer and pathogenic cells in order to flood them with water, causing them to explode, or die due too much liquid - I wonder if that is even possible.
What is the fluid mosaic model?
This is the currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids.
What is the method for preparing cells for electron microscopy called and how was it important in demonstrating visually that proteins are indeed embedded in the phospholipid bilayer of the membrane?
This method is called freeze-fracture. Freeze fracture splits a membrane along the middle of bilayer, somewhat like pulling apart a chunky peanut butter sandwich. When the membrane layers are viewed in the electron microscope, the interior of the bilayer appears cobble stoned, with protein particles interspersed in a smooth matrix, in agreement with the fluid mosaic model. Some proteins remain attached to one layer or the other, like the peanut chunks in the sandwich.
In many animal cells, the uptake of glucose into the cell occurs by a cotransport mechanism, in which glucose is cotransported with Na+ ions. Complete the diagram below using the following steps. -
[Na+] high - A): [glucose] low Glucose-Sodium contransporter - B): glucose (down) and Na+ (down) [Na+] low - C): [glucose] high 1. Na+ moves DOWN its electrochemical gradient 2. Glucose moves AGAINST its concentration gradient (In cotransport, the energy required to move one solute against its concentration or electrochemical gradient is provided by an ion moving into the cell down its electrochemical gradient. The ion that moves into the cell down its gradient is usually the same ion that is pumped out of the cell by an active transport pump: for example, Na+ in animal cells using the sodium-potassium pump, or H+ in plants and prokaryotes using the proton pump. In the case of the glucose-sodium cotransporter in animals, Na+ moves back into the cell down its electrochemical gradient, providing the energy for glucose to move into the cell against its concentration gradient. The energy for glucose transport into the cell is supplied indirectly by the sodium-potassium pump's hydrolysis of ATP, and directly by the Na+ electrochemical gradient created by the pump.)
Which of the following means of transport would most likely be used for moving a medium-sized molecule (like a monosaccharide or an amino acid) from a low concentration on the outside of a cell to a high concentration on the inside of a cell? -
active transport through a "pump" protein
PART B Which variable is the dependent variable--the variable that depended on the treatment and was measured by the researchers? Is the dependent variable on the x-axis or the y-axis? -
concentration of radioactive glucose; on the y-axis
Glucose diffuses slowly through artificial phospholipid bilayers. The cells lining the small intestine, however, rapidly move large quantities of glucose from the glucose-rich food into their glucose-poor cytoplasm. Using this information, which transport mechanism is most probably functioning in the intestinal cells? -
facilitated diffusion
PART C What do the red dots represent? -
the concentration of radioactive glucose found in a 15-day-old guinea pig's red blood cells after different incubation times
