Ch:7 Membrane structure and function

extracellular matric

A (big worms)

Which of the following is true of integral membrane proteins?

C) They are usually transmembrane proteins.

Which of the following is true of the evolution of cell membranes?

D) All components of membranes evolve in response to natural selection.

Which line in the graph represents the bag with the highest initial concentration of sucrose?

a

cytoskeleton

bottom string

what is a ligand

it is a molecule that binds specifically to another molecule, usually a large one

define osmosis

passive transport of water

define hypertonic

reffering to a solution that will make the cell gain water

define hypotinic

reffering to a solution that will make the cell lose water

describe how phospholipids with unsaturated hydrocarbon chains affects membrane fluidity

remains fluid to a lower temperature

cholesterol

4 fused

Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?

A) The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.

According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?

A) They can move laterally along the plane of the membrane.

A protein that spans the phospholipid bilayer one or more times is

A) a transmembrane protein.

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

A) by increasing the percentage of unsaturated phospholipids in the membrane

The presence of cholesterol in the plasma membranes of some animals

A) enables the membrane to stay fluid more easily when cell temperature drops.

The formulation of a model for a structure or for a process serves which of the following purposes?

B) It functions as a testable hypothesis.

Human immunodeficiency virus (HIV) infects cells that have both CD4 and CCR5 cell surface molecules. The viral nucleic acid molecules are enclosed in a protein capsid, and the protein capsid is itself contained inside an envelope consisting of a lipid bilayer membrane and viral glycoproteins. One hypothesis for viral entry into cells is that binding of HIV membrane glycoproteins to CD4 and CCR5 initiates fusion of the HIV membrane with the plasma membrane, releasing the viral capsid into the cytoplasm. An alternative hypothesis is that HIV gains entry into the cell via receptor-mediated endocytosis, and membrane fusion occurs in the endocytotic vesicle. To test these alternative hypotheses for HIV entry, researchers labeled the lipids on the HIV membrane with a red fluorescent dye. What would be observed by live-cell fluorescence microscopy if the red fluorescent lipid dye-labeled HIV membrane fuses with the target cell plasma membrane?

B) The red fluorescent dye-labeled lipids will diffuse in the infected cell's plasma membrane and become difficult to detect.

Some regions of the plasma membrane, called lipid rafts, have a higher concentration of cholesterol molecules. As a result, these lipid rafts

B) are more rigid than the surrounding membrane.

In which of the following would there be the greatest need for osmoregulation?

B) cells of a tidepool animal such as an anemone

Based on the figure above, which of these experimental treatments would increase the rate of sucrose transport into the cell?

B) decreasing extracellular pH

The solutions in the arms of a U-tube are separated at the bottom of the tube by a selectively permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride. Initially, the volume in both arms is the same.

B) side A is hypotonic to side B.

What kinds of molecules pass through a cell membrane most easily?

B) small and hydrophobic

What would be observed by live-cell fluorescence microscopy if HIV is endocytosed first, and then fuses with the endocytotic vesicle membrane?

C) A spot of red fluorescence will move into the infected cell's interior.

Which of the following membrane activities require energy from ATP hydrolysis?

C) Na⁺ ions moving out of a mammalian cell bathed in physiological saline

A patient has had a serious accident and lost a lot of blood. In an attempt to replenish body fluids, distilled water-equal to the volume of blood lost-is transferred directly into one of his veins. What will be the most probable result of this transfusion?

C) The patient's red blood cells will swell because the blood fluid has become hypotonic compared to the cells.

Cell membranes are asymmetrical. Which of the following is the most likely explanation?

C) The two sides of a cell membrane face different environments and carry out different functions.

The cell membranes of Antarctic ice fish might have which of the following adaptations?

C) a high percentage of polyunsaturated fatty

In order for a protein to be an integral membrane protein it would have to be

C) amphipathic, with at least one hydrophobic region.

In a paramecium, cell surface integral membrane proteins are synthesized

C) by ribosomes bound to the rough endoplasmic reticulum.

Cystic fibrosis is a genetic disease in humans in which the CFTR protein, which functions as a chloride ion channel, is missing or nonfunctional in cell membranes.

C) electrogenic ion pumps

What is the voltage across a membrane called?

C) membrane potential

Which of these are not embedded in the hydrophobic portion of the lipid bilayer at all?

C) peripheral proteins

Which of the following types of molecules are the major structural components of the cell membrane?

C) phospholipids and proteins

The difference between pinocytosis and receptor-mediated endocytosis is that

C) pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity.

Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?

CO2

Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells?

D) The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.

In the years since the proposal of the fluid mosaic model of the cell membrane, which of the following observations has been added to the model?

D) The concentration of protein molecules is now known to be much higher.

Why are lipids and proteins free to move laterally in membranes?

D) There are only weak hydrophobic interactions in the interior of the membrane.

If you examine side A after three days, you should find

D) a decrease in the concentration of NaCl and a decrease in the water level.

Ions diffuse across membranes through specific ion channels

D) down their electrochemical gradients.

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

D) integral proteins.

Singer and Nicolson's fluid mosaic model of the membrane proposed that

D) membranes consist of protein molecules embedded in a fluid bilayer of phospholipids.

Which of the following processes includes all others?

D) passive transport

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 be a factor that determines whether the molecule selectively enters the target cells?

D) similarity of the drug molecule to other molecules transported by the target cells

Who was/were the first to propose that cell membranes are phospholipid bilayers?

E) E. Gorter and F. Grendel

When a plant cell, such as one from a peony stem, is submerged in a very hypotonic solution, what is likely to occur?

E) The cell will become turgid.

The phosphate transport system in bacteria imports phosphate into the cell even when the concentration of phosphate outside the cell is much lower than the cytoplasmic phosphate concentration. Phosphate import depends on a pH gradient across the membrane-more acidic outside the cell than inside the cell. Phosphate transport is an example of

E) cotransport.

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?

E) facilitated diffusion

Several epidemic microbial diseases of earlier centuries incurred high death rates because they resulted in severe dehydration due to vomiting and diarrhea. Today they are usually not fatal because we have developed which of the following?

E) hydrating drinks that include high concentrations of salts and glucose Answer: E

When biological membranes are frozen and then fractured, they tend to break along the middle of the bilayer. The best explanation for this is that

E) the hydrophobic interactions that hold the membrane together are weakest at this point.

The primary function of polysaccharides attached to the glycoproteins and glycolipids of animal cell membranes is

E) to mediate cell-to-cell recognition.

The solutions in the two arms of this U-tube are separated by a membrane that is permeable to water and glucose but not to sucrose. Side A is half-filled with a solution of 2 M sucrose and 1 M glucose. Side B is half-filled with 1 M sucrose and 2 M glucose. Initially, the liquid levels on both sides are equal.

Initially, in terms of tonicity, the solution in side A with respect to that in side B is C) isotonic.

Name the four major large molecules of all living things

Lipids, Proteins, Carbohydrates, Nucleic Acids

who proposed the fluid mosaic model? when? describe

S.J. Singer and G. Ncholson proposed in in 1972. this model prposes that membrane proteins are dispersed, individaully inserted into the phospholipid bilayer with their hydrophilic regiona protruding

Which of the following types of molecules are the major structural components of the cell membrane? A) phospholipids and proteins The presence of cholesterol in the plasma membranes of some animals C) enables the membrane to stay fluid more easily when cell temperature drops. In order for a protein to be an integral membrane protein it would have to be B) amphipathic, with at least one hydrophobic region. Water passes quickly through cell membranes because C) it moves through aquaporins in the membrane. Which of the following statements about osmosis is correct? A) The presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis. In which of the following would there be the greatest need for osmoregulation? C) cells of a tide pool animal such as an anemone When a plant cell, such as one from a peony stem, is submerged in a very hypotonic solution, what is likely to occur? A) The cell will become turgid. Active and passive transport of solutes across a membrane typically differ in which of the following ways? B) Active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy. An organism with a cell wall would most likely be unable to take in materials through A) phagocytosis. Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a 0.15 M salt solution become limp and soft. From this we can deduce that B) the fresh water is hypotonic and the salt solution is hypertonic to the cells of the celery stalks. White blood cells engulf bacteria through what process? C) phagocytosis

What name is given to the process by which water crosses a selectively permeable membrane? B) osmosis Endocytosis moves materials _____ a cell via _____. D) into ... membranous vesicles A white blood cell engulfing a bacterium is an example of _____. D) phagocytosis Which of the following best describes the structure of a biological membrane? E) two layers of phospholipids with proteins either crossing the layers or on the surface of the layers A protein that spans the phospholipid bilayer one or more times is C) a transmembrane protein. Which of the following is least likely to be important in holding the components of a biological membrane together? C) covalent interactions between the phospholipid and protein components of the membrane In facilitated diffusion, what is the role of the transport protein? E) Transport proteins provide a hydrophilic route for the solute to cross the membrane. Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells? B) The animal cell is in an isotonic solution, and the plant cell is in a hypotonic The movement of glucose into a cell against a concentration gradient is most likely to be accomplished by which of the following? C) cotransport of the glucose with a proton or sodium ion that was pumped across the membrane using the energy of ATP hydrolysis Which of the following membrane activities requires energy from ATP hydrolysis? C) movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid Why are lipids and proteins free to move laterally in membranes? B) There are only weak hydrophobic interactions in the interior of the membrane.

what are aquaporins

a channel protein in the plasma membrane of cells that specifically facilitates osmosis

distinguish between glycolipids and glycoproteins

a glycolipid is a lipid attached to carbohydrates while glycoproteins are pretiens attached to carbohydrates

major functions: signal transduction

a membane protein may have a binding site with a shape of a chemcial messenger. external messengers can cause a shape change in the messenger protein

describe the Davson-Danielli model of membranse structure. what were 2 problems with it?

a phospholip bilayer between 2 layers of protien. problem 1: generalization that all membranes of the cells were identical. Prolem 2: protein placement was wrong

major functions:transport

a protein can provide a hydrophilic channel across the membrane or it can move substances from one side to the other by changing shape

major functions: enzymatic activity

a protein in the membrane can be an enzume with its active site, several of the enzymes can form a team that carries out steps of a metablic pathway

Which line or lines in the graph represent(s) bags that contain a solution that is hypertonic at 50 minutes?

b

why dont plant cells burst in hypertonic solutions?

because the cell wall holds it in place

Five dialysis bags, constructed from a semipermeable membrane that is impermeable to sucrose, were filled with various concentrations of sucrose and then placed in separate beakers containing an initial concentration of 0.6 M sucrose solution. At 10-minute intervals, the bags were massed (weighed) and the percent change in mass of each bag was graphed. Which line in the graph represents the bag that contained a solution isotonic to the 0.6 M solution at the beginning of the experiment?

c

An animal cell lacking oligosaccharides on the external surface of its plasma membrane would likely be impaired in which function?

cell-cell recognition

define endocytosis

cellular uptake of biological molecules and particle matter via formation of new vesicles

distinguish between channel proteins and carrier proteins

channell proteins provide a channell that certain molecules or ions can use. carrier proteins change shapes to allow passengers to pass through

Which component is a glycolipid?

connected to phospholipids ; bubbles b

Which component is the peripheral protein?

d (embedded)

ATP (adenosine triphosphate) Releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells. amphipathic Having both a hydrophilic region and a hydrophobic region. aquaporin A channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis, the diffusion of water across the membrane. carbohydrate A sugar (monosaccharide) or one of its dimers (disaccharides) or polymers (polysaccharides). concentration gradient A region along which the density of a chemical substance increases or decreases.

diffusion The spontaneous movement of a substance down its concentration gradient, from a region where it is more concentrated to a region where it is less concentrated. electrochemical gradient The diffusion gradient of an ion, which is affected by both the concentration difference of the ion across a membrane (a chemical force) and the ion's tendency to move relative to the membrane potential (an electrical force). electrogenic pump An ion transport protein that generates voltage across a membrane. active transport The movement of a substance across a cell membrane, with an expenditure of energy, against its concentration or electrochemical gradient; mediated by specific transport proteins.

crossing the membrane: CO2

dissolve in lipid bilayer and cross with the help of membrane proteins

crossing the membrane: O2

dissolve in lipid bilayer and cross with the help of membrane proteins

what are the 2 forces that drive difusion of ions across the membrane

electirical and chemical forces. the combination of them is called electrohemical gradient

glycoprotein A protein with one or more carbohydrates covalently attached to it. hypertonic Referring to a solution that, when surrounding a cell, will cause the cell to lose water. hypotonic Referring to a solution that, when surrounding a cell, will cause the cell to take up water. integral protein Typically a transmembrane protein with hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane and with hydrophilic regions in contact with the aqueous solution on either side of the membrane (or lining the channel in the case of a channel protein). ion channel A transmembrane protein channel that allows a specific ion to flow across the membrane down its concentration gradient. isotonic Referring to a solution that, when surrounding a cell, has no effect on the passage of water into or out of the cel

endocytosis Cellular uptake of biological molecules and particulate matter via formation of new vesicles from the plasma membrane. exocytosis The cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane. facilitated diffusion The spontaneous passage of molecules or ions across a biological membrane with the assistance of specific transmembrane transport proteins. flaccid Limp. Lacking in stiffness or firmness, as in a plant cell in surroundings where there is no tendency for water to enter the cell. gated channel A transmembrane protein channel that opens or closes in response to a particular stimulus. glycogen An extensively branched glucose storage polysaccharide found in the liver and muscle of animals; the animal equivalent of starch. glycolipid A lipid with covalently attached carbohydrate(s).

what is membrane potential

it is the coltage across a membrane. the outside of the membrane is positive. the inside is negative

what is cotransport

it is the coupleing of the downhill diffusion of one substance with the uphill transport of another against its concentration gradient

waht is active transport?

it is the movement of substances across a cell membrane with a release of energy. it goes against the concentration gradient. carrier proteins are involved. ATP supplies the power for this proccess

what is facilitated diffusion

it is the spontaneous pasage of molecules or ions through a biological membrane with the asistance of specific proteins. it is passive transport

what is membrane fluidity? descirbe movements seen in the fluid

it means that membranes are not locked in place, they can move because of weak bonds it experiences. the movements are lateral

Explain what is meant when we say a molecule is amphipathic

it means the molecule has a hydrophobic and a hydrohilic region

pinocytosis A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes. plasma membrane The membrane at the boundary of every cell that acts as a selective barrier, regulating the cell's chemical composition. plasmolysis A phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall; occurs when the cell loses water to a hypertonic environment. proton pump An active transport protein in a cell membrane that uses ATP to transport hydrogen ions out of a cell against their concentration gradient, generating a membrane potential in the process. receptor-mediated endocytosis The movement of specific molecules into a cell by the inward budding of membranous vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances. selective permeability A property of biological membranes that allows them to regulate the passage of substances. sodium-potassium pump A transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell. tonicity The ability of a solution surrounding a cell to cause that cell to gain or lose water. transport protein A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane. turgid Swollen or distended, as in plant cells. (A walled cell does this if it has a greater solute concentration than its surroundings, resulting in entry of water.)

ligand A molecule that binds specifically to another molecule, usually a larger one. low-density lipoprotein (LDL) A particle in the blood made up of cholesterol and other lipids surrounded by a single layer of phospholipids in which proteins are embedded. Carries more cholesterol than a related lipoprotein. membrane potential The difference in electrical charge (voltage) across a cell's plasma membrane due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances. model A representation of a theory or process. myosin A type of protein filament that acts as a motor protein with actin filaments to cause cell contraction. osmoregulation Regulation of solute concentrations and water balance by a cell or organism. osmosis The diffusion of water across a selectively permeable membrane. passive transport The diffusion of a substance across a biological membrane with no expenditure of energy. peripheral protein A protein loosely bound to the surface of a membrane or to part of an integral protein and not embedded in the lipid bilayer. phagocytosis A type of endocytosis in which large particulate substances are taken up by a cell. It is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells).

define flaccid

limp

describe how cholestorol affects membrane fluidity

makes membranes less fluid at higer temperatures

major functions:intercellular joining

membrane proteins of adjacent cells may hook together at junctions

major functions: attachment to cytoskeleton and ECM

microfilaments or other parts of cytoskeleton may be noncovalently bound to a membrane proteins. proteins bounded to ECM molecules can coordinate cellular changes

define receptor-mediated enocytosis

movement of specific molecules into a cell by the inward budding of membranous vesciles

describe peripheral proteins

not appended in the lipid bilayer, appendages loosely bound to the surface of the membrace

define exocytosis

opposite of endocytosis

crossing the membrane: H+

pass through a hydrophillic channell

describe integral protiens

penetrate the hydrophobic core of the lipid bilayer

define isotonic

reffering to a solution that has no effect on water

major functions: cell-cell recognition

some glycoproteins serve as indentification tags recognized by membrane proteins of other cells

define turgid

swollen or distended

define passive transport

the diffusion of a substance across a biologcal membrane

define diffusion

the movement of molecules so that they spread evenly in the available space

describe how decreasing temperature affects membrane fluidity

the phopholipids pack together and the mebrane solidifies

defince concetration gradient

the region along which the density of a chemical substance

are transport proteins specific?

they are specific for the substance it translocates

define pinocytosis

type of endocytosis, cell ingests extracellular fluid and its dissolved solutes

define phagocytosis

type of endocytosis, large molecules are taken up by the cekk

crossing the membrane: glucose

use carrier proteins, hold onto their passengers and change shape to pass through the membrane

crossing the membrane: H2O

water molecules pass through aquaporins at the rate o about 3 billion a second

define plasmolysis

when the cytoplasm shrivels and the plasma membrane pulls away from the cell wall, occurs when the cells lose too much water