AP Biology Chapter 7

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* There are two classes of membrane transport proteins—carriers and channels. Both form continuous protein pathways across the lipid bilayer. Whereas transport by carriers can be either active or passive, solute flow through channel proteins is always passive.

Carrier molecules in the membrane and metabolic energy are required for A. Active transport. B. Facilitated diffusion, active transport, and osmosis. C. Facilitated diffusion and active transport. D. Osmosis. E. Facilitated diffusion.

A

What mechanisms do plants use to load sucrose produced by photosynthesis into specialized cells in the veins of leaves? A. An electrogenic pump, a proton pump, and a contransport protein B. An electrogenic pump and a contransport protein C. A proton pump D. A contransport protein E. An electrogenic pump

A

Hypotonic

A cell is in a hypotonic environment if that environment has fewer dissolved particles and more water. Water will move into the cell; if too much water moves it, bursting can occur.

Freeze-Fracture Method

A method of preparing cells for electron microscopy which has has visually demonstrated that proteins are indeed embedded in the phospholipid bilayer of the membrane. This technique helped prove Singer and Nicholson's theory correct. Freeze fracture splits a membrane along the middle of the phospholipid bilayer. When the membrane is then assessed, it is seen that the interior of the bilayer has proteins interspersed in a smooth matrix.

What is the ideal tonicity for a plant?********* Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells? A. The animal cell is in a hypertonic solution, and the plant cell is in a hypotonic solution. B. The animal cell is in a hypotonic solution, and the plant cell is in an isotonic solution. C. The animal cell is in an isotonic solution, and the plant cell is in a hypertonic solution. D. The animal cell is in a hypertonic solution, and the plant cell is in an isotonic solution. E. The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.

A plant wants to be in a hypotonic solution. This means that there are fewer dissolved particles and more water so water will move inside, helping the plant store water in its vacuole. E

Contransport

A single ATP powered pump that transports a specific solute can indirectly drive the active transport of other solutes, this is called cotransport.

Electrogenic Pump

A transport protein that generates voltage across a membrane, sodium potassium pump is main example. For animals. Causes voltage.

How does exocytosis work?

A transport vesilcle from the Golgi moves along microtubules of the cytoskeleton to the plasma membrane. When the vesicle and plasma membrane come in contact, the lipid molecules of the two bilayers rearrange themselves so that they fuse. The content of the vesicle then spill to the outside of the cell. Proteins made in ER then go to Golgi to be modified (via a vesicle). Subsequently, they go via vesicle towards the membrane and then get exported out of the cell when the membranes fuse. In addition to secreting molecules, exocytosis is used when making a plant wall as it delivers proteins and carbs from the Golgi to the extracellular matrix.

Sodium Potassium Pump

Active transport- exchanges Na+ for K+ across the plasma membrane. Pumps ions against concentration gradient. Sodium ions are high outside and low inside, while potassium ions are low outside and high inside. The pump translocates 3 sodium ions out for every 2 potassium ions pumped in. The pump already has a higher concentration of sodium outside but it keeps pumping it out. Vice versa with K.

Voltage

All cells have voltage across their membranes. Voltage refers to the electrical potential energy- a separation of opposite charges. The cytoplasm is negative in relation to extracellular fluid which is positive because of unequal distribution of cations and anions.

The surface of integral proteins are what?

Amphipathic

What gives animal cells a stronger framework than the plasma membrane would provide by itself?

Attachments of proteins on both the cytoplasmic side and the aqueous side-On the cytoplasmic side, some membrane proteins are held together by attachment to the cytoskeleton. On the extracellular side, certain membrane proteins are attached to fibers on the matrix.

Explain why cholesterol can be referred to as a "temperature buffer."

Because at relatively high temperatures such as body temperature, 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. Cholesterol can make a membrane less fluid by restricting phospholipid movement Cholesterol can make a membrane more fluid by disrupting the close packing of phospholipids.

Why does water move quickly through the membrane?

Because it travels through aquaporins.

Why do processes like endocytosis/exocytosis even occur?

Because the bulk transport is too big and needs help from a vesicle.

Cytolysis

Bursting of a cell due to too much water coming in. Hypotonic solution.

The movement of potassium into an animal cell requires A. High cellular concentrations of potassium. B. Low cellular concentrations of sodium. C. An energy source such as ATP or a proton gradient. D. A cotransport protein. E. A gradient of protons across the plasma membrane.

C

Which of the following characterizes the sodium-potassium pump? A. Sodium ions are pumped out of a cell against their gradient and potassium ions are pumped into a cell against their gradient. B. Potassium ions are pumped into a cell against their gradient. C. Sodium ions are pumped out of a cell against their gradient, potassium ions are pumped into a cell against their gradient, and the pump protein undergoes a conformational change. D. Sodium ions are pumped out of a cell against their gradient. E. The pump protein undergoes a conformational change.

C

Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a salt solution become limp and soft. From this we can deduce that the cells of the celery stalks are a. hypotonic to both fresh water and the salt solution. b. hypertonic to both fresh water and the salt solution. c. hypertonic to fresh water but hypotonic to the salt solution. d. hypotonic to fresh water but hypertonic to the salt solution. e. isotonic with fresh water but hypotonic to the salt solution.

C The solution (water is hypotonic) so the cell is hypertonic as water moves in.

Plasmolysis

Cell shriveling and dying due to a lack of water- hypertonic.

What is the difference between channel proteins and carrier proteins?

Channel proteins have a hydrophilic channel so that water or other small molecules can get into the membrane. Carrier proteins undergo a change in shape that translocates the solute binding site across the membrane. Unlike channel proteins which only transport substances through membranes passively, carrier proteins can transport ions and molecules either passively through facilitated diffusion, or via secondary active transport.

Electrochemical Gradient

Combination of the chemical force and the electric force on the ion's movement. The inside of the cell (cytosol) is negative whereas the outside is positive. Anions are to go out of the cell and cations are to come in in order to balance everything . An ion does not just go down its concentration gradient, it goes down its electrochemical gradient.

In most cells, there are electrochemical gradients of many ions across the plasma membrane even though there are usually only one or two electrogenic pumps present in the membrane. The gradients of the other ions are most likely accounted for by

Cotransport Proteins

The sodium-potassium pump in animal cells requires cytoplasmic ATP to pump ions across the plasma membrane. When the proteins of the pump are first synthesized in the rough ER, what side of the ER membrane will the ATP binding site be on?

Cytoplasmic side of ER

The membrane activity most nearly opposite to exocytosis is a. plasmolysis. b. osmosis. c. facilitated diffusion. d. phagocytosis. e. active transport.

D

The selective permeability of biological membranes is dependent on which of the following? a. the type of transport proteins that are present in the membrane b. the lipid bilayer being permeable to primarily small, nonpolar molecules c. the types of carbohydrates on the surface of the membrane d. A and B only e. A, B, and C

D

a large amount of distilled water was transferred directly into one of his veins. What will be the most probable result of this transfusion? a. It will have no unfavorable effect as long as the water is free of viruses and bacteria. b. It will have serious, perhaps fatal, consequences because there will be too much fluid for the heart to pump c. It will have serious, perhaps fatal, consequences because the red blood cells will be hypotonic relative to the body fluids and the cells will shrivel. d. It will have serious, perhaps fatal, consequences because the red blood cells will be hypertonic relative to the body fluids and the cells will burst. e. It will have no serious effect because the kidneys would quickly eliminate the excess water.

D

An organism with a cell wall would have the most difficulty doing which process? a. diffusion b. osmosis c. active transport d. phagocytosis e. exocytosis

D, plants don't do phagocytosis because

Cholesterol enters cells via A. Phagocytosis. B. Pinocytosis. C. Osmosis. D. Exocytosis. E. Receptor-mediated endocytosis.

E

What membrane-surface molecules are thought to be most important as cells recognize each other? a. phospholipids b. integral proteins c. peripheral proteins d. cholesterol e. glycoproteins

E

Pinocytosis

Form of endocytosis. Means "cellular drinking." A cell "gulps" drops of fluid into tiny vesicles. The cell doesn't need the fluid but needs the molecules dissolved in the liquid.

Phagocytosis

Form of endocytosis. Means "cellular eating." A cell engulfs a particle by wrapping pseudopodia (temporary projection) around it and packaging it within a vesicle/vacuole. The particle is then digested by the cell after the vacuole fuses with a lysosome containing hydrolytic enzymes.

Selective Permeability

Fundamental characteristic of plasma membrane which refers to its ability to allow some substances in more easily than others, thereby controlling traffic into and out of the cell.

What are functions of the glycolipids and glycoproteins?

Glycoproteins help stabilize and maintain shape for the cell membrane. Glycolipids serve as markers for cell to cell communication and to provide energy.

Flaccid

If the plant's environment is isotonic, there is no net tendency for water, so the plant cell is considered flaccid, or limp.

Isotonic

In an animal cell (no wall), a cell immersed in an isotonic solution will have no net movement of water across the membrane. Water does indeed flow across the membrane, but it goes both ways.

Secondary Active Transport

In secondary active transport, one species of solute moves along its electrochemical gradient, allowing a different species to move against its own electrochemical gradient. This movement is in contrast to primary active transport, in which all solutes are moved against their concentration gradients, fueled by ATP. symporter- one going against gradient and other going with but in same direction Antiport-opposite directions Both use ATP Both types of cotransporter

What is one of the ways that the membranes of winter wheat are able to remain fluid when it is extremely cold?

Increasing percentage of unsaturated fats

What are the two major types of membrane proteins?

Integral proteins and peripheral proteins.

Proton Pump

Main electrogenic pump for plants which transports hydrogen ions out of the cell. Intentionally build up protons or H+ on outside of cell by pumping them out against their gradient. Same as Sodium Potassium Pump, except it only goes out.

Diffusion (passive)

Movement of molecules of any substance so that they spread out evenly into the available space

Discuss the permeability of the plasma membrane in regard to polarity

Nonpolar (hydrophobic) molecules such as hydrocarbons and oxygen can get in and out of a cell rapidly because they dissolve in the nonpolar bilayer. However, the hydrophobic core of the membrane impedes the direct passing of polar molecules, which are hydrophilic. Polar molecules such as glucose and water pass very slowly, hence the need for aid from proteins. (transport). An ion runs into the problem of not being able to pass with ease as well.

Peripheral proteins

Not embedded in the bilayer, they are appendages loosely bounded to surface, often exposed to integral proteins. Can rest on top of integral protein. A hormone might be a peripheral protein-it'll attach to the cell, do its job and then leave. Since it is on the peripheral, it easily goes away.

Osmoregulation

Organisms without cell walls must have special adaptations for the control of water balance. For example, the paramecium lives in ponds, an environment which is hypotonic to the cell, therefore the cell wants to intake water. However, to combat the chance of bursting, the paramecium has a membrane much less permeable to water than most, consequently slowing the intake of water. This only slows however, what stops it from bursting is the contractile vacuole which forces water out rapidly.

The original model for the bilayer structure of cell membranes, which was prepared in the 1920s, was based on what?

The idea that phospholipids are amphipathic, hence the diagram separating the tails and the heads.

The lateral mobility (fluidity) of lipids and proteins in membranes is a consequence of what?

The noncovalent bonds between the lipid and protein components & weak hydrophobic interactions

What determines most of the membrane's functions?

The proteins embedded in the bilayer.

Which factors affect the rate of osmotic movement of water?

The rate of osmosis increases with increasing differences between two solutions separated by a selectively permeable membrane.

What would happen if contractile vacuoles stopped working?

The reason paramecia have those vacuoles is to pump excess water out of their little one-celled bodies. Water continually enters their bodies because there is a higher concentration of substances inside them than outside. The water doesn't naturally go back outside in the same way that it comes in; the cell wall is like a one-way street; it lets water in, but not out. So, to keep the pressure constant inside, the contractile vacuoles pump out the extra water. So, if they didn't have those vacuoles it would not be able to get rid of the water rushing in from the salty solution so it would burst.

Fluid Mosaic Model

This term describes the setup of the plasma membrane- the membrane is a fluid like substance which is selectively permeable with a plethora of proteins embedded throughout the bilayer of phospholipids. Such a double layer of molecules exists as a stable boundary between two aqueous compartments due to the hydrophobic tails and the hydrophilic heads.

True or False: During plasmolysis the organelles of a plant cell clump together.

True

Aquaporin

Type of channel protein (transport protein) that helps channel water into the membrane.

Active Transport

Way of moving molecules against the concentration gradient with the assistance of ATP.

6 major functions performed by proteins of the plasma membrane

a) transport proteins-(type of integral protein) - channel proteins and carrier proteins: channel proteins help transport substances across the bilayer. A protein might provide a hydrophilic channel across the membrane. carrier proteins help get a molecule from outside the cell by protecting the substance so it can be taken in safely. Unlike channel proteins, carrier proteins can go against the concentration gradient. b) enzymatic proteins- a protein built into the membrane may be an enzyme with its active site exposed to the solution. Enzymatic proteins catalyze reactions. c) signal proteins- may have a binding site with a specific shape that fits the shape of the chemical messenger, such as a hormone. The external messenger (signaling molecule) may case a shape change in the protein. d) cell-cell recognition proteins- serve as identification tags that can be recognized by other proteins e) intercellular joining- membrane proteins of adjacent cells might join together to form junctions f) attachment to cytoskeleton and extra cellular matrix- microfilaments or other parts of the cytoskeleton might be noncovalently bound to membrane proteins, function that helps maintain cell shape and stabilizes location of certain proteins.

What were the problems with the Sandwich Model of the lipid bilayer?

1) This model assumes that all bilayers are the same. Membranes have different amount of proteins, different location of proteins. The plasma membrane for example is 7-8 nm thick whereas the membrane of a mitocondria is 6 nm thick and looks like a row of beads. Mitochondrial membranes also have a higher percentage of proteins and different kinds of lipids. In short, membrane function differs as a result of the different structures present. 2) A second, more serious problem was protein placement. Unlike proteins dissolved in the cytosol, membrane proteins are not very soluble in water, because they are amphipathic. If the sandwich model was right and such proteins were layered on the surface of the membrane, their hydrophobic regions would be exposed to water.

Describe step by step how the Sodium Potassium Pump works

1) cytoplasmic NA+ binds to the pump (a protein), the affinity for NA+ is high when the pump is in this shape. 2) NA +binding stimulates the phosphorylation (adding of a phosphate group) via ATP. Now there is a "P" by the pump. 3) Phosphorylation causes the pump to change shape, decreasing affinity for NA+ which leads NA+to be exported out of the cell. 4) the new shape has a high affinity for K+ which triggers the release of the P. 5) Loss of P makes the pump go back to its original shape, thus releasing K+ into the cell, thus restarting the cycle.

Hypertonic

A cell is in a hypertonic environment if that environment has more dissolved particles than water. Water will be moving out of the cell in order to balance the many dissolved particles and lack of water. This can cause the cell to lose too much water, shrivel, and die.

How does an ion diffuse?

An ion does not simply diffuse down its concentration gradient but diffuses down its electrochemical gradient. For example, there is a higher concentration of Na+ outside a resting nerve cell than inside. When the neuron is stimulated, a gated channel opens and Na+ diffuse into the cell down their electrochemical gradient. The diffusion of Na+ is driven by their concentration gradient and by the attraction of cations to the negative side of the membrane.

Antiporter

Antiporter is an exchanger which means that sodium is going down the gradient and this fuels taking the calcium ions outside of the cell, against its concentration gradient. Cotransporter-same direction, antiporter-opposite direction. Sodium potassium pump is not an antiporter because in an antiporter, one thing is going against and other is going with. Although s-p pump meets the requirement of opposite directions, since both substances are going against the gradient, it isn't an antiporter. Not a cotransporter either because K and NA are going against their gradients.

Some regions of the plasma membrane, called lipid rafts, have a higher concentration of cholesterol molecules. At higher temperatures, these regions _____.

Are less fluid than surrounding membrane so that we don't become a liquid. At lower temperatures, cholesterol helps the plasma membrane remain fluid, here it's opposite. Cholesterol can make a membrane less fluid by restricting phospholipid movement Cholesterol can make a membrane more fluid by disrupting the close packing of phospholipids. As distance between phospholipids increase (due to presence of cholesterol) fluidity increases-you want this in the cold. High temp-fluidity decrease because of cholesterol low temp-fluidity increase because of it

How does the proton pump relate to cotransport?

As the hydrogen + ions are transported out of the cell in order to store energy. When these H+ try to get away from one another, energy can be captured. This allows nature to store energy on one side. ATP is used. As this proton pump is doing its job, it can indirectly drive the transport of another solute. This is cotransport. A substance that has pumped across the membrane (the H+ ions going inside) can do work as it comes back outside, just like water pumped up a hill doing work as it comes back down. The cotransporter which is another transport protein, separate from the pump couples the downhill movement of the H+ (downhill because its going into the cell- concentration of high to low) with the uphill movement of sucrose molecules so that the cell can get the sugar it needs to carry out cellular respiration. Sucrose can now get into the cell but can only do this if it travels with a hydrogen ion. The hydrogen ion benefits from this as it uses the contransporter to easily diffuse.

After a membrane freezes and then thaws, it often becomes leaky to solutes. The most reasonable explanation for this is that A. Transport proteins become nonfunctional during freezing. B. The integrity of the lipid bilayer is broken when the membrane freezes. C. The lipid bilayer loses its fluidity when it freezes. D. The solubility of most solutes in the cytoplasm decreases on freezing. E. Aquaporins can no longer function after freezing.

B

An animal cell lacking oligosaccharides on the external surface of its plasma membrane would likely be impaired in which function? a. transporting ions against an electrochemical gradient b. cell-cell recognition c. maintaining fluidity of the phospholipid bilayer d. attaching to the cytoskeleton e. establishing the diffusion barrier to charged molecules

B

The main difference(s) between facilitated diffusion and active transport is (are) A. Facilitated diffusion does not rely on cellular energy and active transport does. B. Facilitated diffusion moves substances down their concentration gradient and active transport moves them against their gradient, facilitated transport does not rely on cellular energy and active transport does, and facilitated transport uses channel or carrier proteins and active transport does not. C. Facilitated diffusion uses channel or carrier proteins and active transport does not. D. Facilitated diffusion moves substances down their concentration gradient and active transport moves them against their gradient and does not rely on cellular energy and active transport does.

B

Why is a combination of saturated and unsaturated fats very important?

Because if we were all saturated, we would be too rigid (saturated fats are solid at room temperature) but if we were all unsaturated, then we'd have too much liquid as unsaturated fats are liquid at room temperature. Animals in the cold have more unsaturated fats because saturated fats would solidify in such cold weather. (saturated fats-rigidity). A membrane remains fluid as temperature decreases until finally the the phospholipids settle into a closely packed arrangement and solidify. The temperature at which a membrane solidifies depends on the type of lipids it is made out of. The membrane remains fluid to a lower temperature if it has a lot of phospholipids with unsaturated hydrocarbon tails. This is because unsaturated tails cannot pack as closely together, thus leaving it a liquid for longer.

Why must membranes be fluid in order to work properly?

Because when a membrane solidifies, its permeability changes and enzymatic proteins may not work properly anymore. For example, enzymatic proteins may become inactive if they need to be able to move freely around but the membrane has already solidified. The lipid composition of cell membranes can change as an adjustment to weather. For instance, in many plants that tolerate cold, unsaturated fats will increase so they do not solidify. (unsaturated are liquid).

All of the following are functions of integral membrane proteins except A. Cytoskeleton attachment. B. Active transport. C. Protein synthesis. D. Cell adhesion. E. Hormone reception.

C

If a membrane protein in an animal cell is involved in the cotransport of glucose and sodium ions into the cell, which of the following is most likely not true? a. The sodium ions are moving down their electrochemical gradient. b. Glucose is entering the cell against its concentration gradient. c. Sodium ions can move down their electrochemical gradient through the cotransporter whether or not glucose is present outside the cell. d. The higher sodium ion concentration outside the cell is the result of an electrogenic pump. e. A substance that blocked sodium ions from binding to the cotransport protein would also block the transport of glucose.

C

In addition to exporting materials from the cytoplasm of the cell, the process of exocytosis is also important in A. Maintaining the osmotic balance between the cytoplasm and the cell exterior. B. The increase in the size of cells. C. The production of cell walls by plant cells. D. The production of cell walls by plant cells, the increase in the size of cells, and maintaining the osmotic balance between the cytoplasm and the cell exterior E. The production of cell walls by plant cells and the increase in the size of cells.

C

What kinds of molecules pass through a cell membrane most easily? A. Ionic B. Large polar C. Small and hydrophobic D. Large and hydrophobic E. Monosaccharides such as glucose

C, nonpolar get in quickly, hydrophobic=nonpolar

What type of protein assists in active transport by helping them flow down the gradient?

Carrier, not channel. This makes sense because channel proteins merely allow particles to go through by opening up as opposed to carrier which can actually move the molecule/s.

When is the cell wall of no advantage?

Cell walls help stop water from causing the cell to lyse, but it's no use when the solution is hypertonic, or has more dissolved particles. Here water will move out of the cell, something which can cause plasmolysis, in both types of cells.

What effect does cholesterol have on the cell membrane?

Cholesterol lowers membrane fluidity at normal temperatures by reducing phosholipid movement. At low temperatures, it hinders solidification by disrupting the regular packing of phospholipids. *enables the membrane to stay fluid more easily when cell temperature drops.*

Discuss cholesterol in regard to receptor mediated endocytosis.

Cholesterol travels in the blood in particles called low density lipoproteins. Low density lipoproteins act as ligands by binding to low density lipoprotein receptors and getting into the cell. If someone has familial hypercholesterolemia, the low density lipoproteins are missing or defective so cholesterol can't get into the cell correctly. Instead, cholesterol accumulates in the blood where it contributes to early atherosclerosis, the buildup of lipid deposits within blood vessels-the vessels then bulge inward thereby narrowing the vessel and impeding blood flow.

The sodium-potassium pump is called an electrogenic pump because it A. Pumps hydrogen ions out of the cell. B. Is used to drive the transport of other molecules against a concentration gradient. C. Ionizes sodium and potassium atoms. D. Contributes to the membrane potential. E. Pumps equal quantities of Na+ and K+ across the membrane.

D

Passive Transport

Diffusion of a substance across a membrane with no ATP required.

Of the following functions, which is most important for the glycoproteins and glycolipids of animal cell membranes? a. facilitated diffusion of molecules down their concentration gradients b. active transport of molecules against their concentration gradients c. maintaining the integrity of a fluid mosaic membrane d. maintaining membrane fluidity at low temperatures e. a cell's ability to distinguish one type of neighboring cell from another

E

The difference between pinocytosis and receptor-mediated endocytosis is that A. Pinocytosis requires cellular energy, but receptor-mediated endocytosis does not. B. Pinocytosis increases the surface area of the plasma membrane whereas receptor-mediated endocytosis decreases the plasma membrane surface area. C. Pinocytosis can concentrate substances from the extracellular fluid, but receptor-mediated endocytosis cannot. D. Pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity. E. Pinocytosis brings only water into the cell, but receptor-mediated endocytosis brings in other molecules as well.

E

The movement of potassium into an animal cell requires A. Low cellular concentrations of sodium. B. A gradient of protons across the plasma membrane. C. High cellular concentrations of potassium. D. A cotransport protein. E. An energy source such as ATP or a proton gradient.

E

You are working on a team that is designing a new drug. In order for this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would not be a factor that determines whether the molecule enters the cell? a. size of the drug molecule b. polarity of the drug molecule c. charge on the drug molecule d. similarity of the drug molecule to other molecules transported by the target cells e. lipid composition of the target cells' plasma membrane

E

Explain how the type of hydrocarbon tails of the phospholipid bilayer affect its fluidity.

If there are unsaturated fatty acids, than there are kinks (separations) in the tails. This makes it a lot more fluid. If there are saturated hydrocarbon tails, the phospholipids cannot move around as much. This explains why animals in the cold tend to have unsaturated hydrocarbon tails.

What is endocytosis and how does it work?

In endocytosis, the cell takes in biological molecules by forming vesicles. The substance nears the cell and pinches into the membrane, thus forming a vesicle, thereby allowing the substance to enter the cell.

When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are what?

Integral proteins

Discuss the fluidity of the plasma membrane

Membranes are not static sheets of molecules locked rigidly in place. A membrane is held together primarily by hydrophobic interactions which are weaker than covalent bonds. Most of the lipids and some of the proteins can shift about across the plane of the membrane. However, it is rare for the molecule to go to the other layer because this would involve the hydrophilic part of the molecule to cross the hydrophobic core. When we are cold, we shiver, the moving of the phospholipids helps generate heat as well.

Facilitated Diffusion

Passive transport aided by proteins, important because many hyrophilic molecules can't get in on their own, or can get in but take a long time.

Integral proteins

Penetrate hydrophobic core, many are transmembrane proteins which means that they span the membrane, others only extend partway into the hydrophobic core. Integral proteins are amphipathic. Their hydrophobic regions consist of one or more stretches of nonpolar amino acids usually coiled into alpha helices. The hydrophilic parts are exposed to water on either side. Some integral proteins also have a channel through their center which allows the passage of hydrophilic substances. STUCK INSIDE CELL MEMBRANE, very difficult to remove!

Tonicity

The ability of a solution to cause a cell to lose or to gain water.

Osmosis

The diffusion of water across a selectively permeable membrane.

Discuss the lateral movement of organic compounds

The lateral movement of phospholipids within the membrane is rapid. Proteins are much larger and therefore move less. Some membrane proteins move in a highly directed manner, perhaps along cytoskeletal fibers by motor proteins connected to the membrane proteins' cytoplasmic regions.

Explain the membrane potential in terms of a battery.

The membrane potential acts like a battery, an energy source that that affects the traffic of all charged particles into and out oft the cell. Because the inside is negative and the outside is positive, the membrane favors cations to come in and anions to go out in hopes of reaching equilibrium.

Discuss the structure of the plasma membrane

The staple ingredients of the plasma membrane are proteins and lipids, although carbohydrates are also important. The most abundant type of lipid is the phospholipid, which folds over on itself. The phospholipid bi layer which makes up the cell membrane has hydrophobic tails and hydrophilic heads. A phospholipid is an amphipathic molecule which means that if contains both hydrophobic and hydrophilic regions. Furthermore, most of the proteins within membranes also have amphipathic characteristics.

What is the simple rule of diffusion? Assume that there is an absence of all other forces such as ATP.

The substance will diffuse from where it is more concentrated to where it is less concentrated, hence diffusing down its concentration gradient.

What is special about transport proteins?

They are specific for the substance it moves

Why can't cells do phagocytosis (or any type of endocytosis)

They have a cell wall so the membrane cannot expand

Discuss the development of the membrane model

Two dutch scientists, E. Gorter and F. Grendel made the discovery of the phospholipid bilayer. The next question was where the proteins are located within the membrane. Although the heads are hydrophilic, the surface of a phospholipid bilayer adheres less strongly to water than the surface of a biological membrane such as that of mitochondria. Hugh Davson and James Danielli proposed that outside the hydrophobic zone of the tails there were hydrophilic proteins on both sides. This is called the sandwich model as there is a phospholipid bilayer between 2 layers of proteins. This was widely accepted until the 60s.

Ion channel

Type of channel protein (which is a type of transfer protein) many of which function as gated channels, which open or close in response to a stimulus-electrical or chemical. Gated channels only open if a trigger is hit when the voltage reaches a certain amount.

Receptor Mediated Endocytosis

Type of endocytosis in which cells absorb molecules by using receptor proteins. Makes use of receptors attached to the cell membrane to engulf molecules. In this technique, only specific molecules that get bound to the receptors can be engulfed into the cell. RME allows cells to acquire bulks of specific substances even if they are not very concentrated in the extracellular fluid. In the membrane, there are specific receptor sites exposed to the extracellular fluid. The specific substances (ligands- any molecule that binds specifically to a receptor site of another molecule) bind to those receptors. When bound, a vesicle with the ligands is created and imported into the cell. Used to take in cholesterol.

Turgid

Very firm, healthy state for plants, means that their cell wall is doing its job by not allowing cytolysis to occur.

Membrane Potential

Voltage difference across membrane because of unequal distribution of ions-think of sodium potassium pump, for every 3 NA+ that go out, only 2 K+ come in, this causes unbalance. LIKE CHARGES REPEL SO THEY'RE NOT TRYING TO REACH HOMEOSTASIS.

How do cell walls help water balance?

When a cell with a wall is immersed in a hypotonic solution such as rain water, the cell walls helps maintain the water balance. Like an animal cell, the plant cell swells as water enters by osmosis. However, the relatively inelastic wall will only expand so much before it exerts a back pressure on the cell that opposes more water intake. This state is called turgid-very firm.

You have a planar bilayer with equal amounts of saturated and unsaturated phospholipids. After testing the permeability of this membrane to glucose, you increase the proportion of unsaturated phospholipids in the bilayer. What will happen to the membrane's permeability to glucose?

Will increase

What is the role of membrane carbohydrates in cell-cell recognition?

a cell's ability to distinguish one type of neighboring cell from another is very important. some membrane carbohydrates are covalently bonded to lipids, therefore forming glycolipids. However, most are covalently bonded to proteins (carb + protein) to form a glycoprotein.