218 test 3

double bonds in hydrocarbon tails have what effect on phospholipid tails and the rigidity of the lipid bilayer?

double bonds decrease the ability of hydrocarbon tails to pack together, which makes the bilayer less stiff

porin proteins-which form large, water-filled pores in mitochondrial and bacterial outer membranes-fold into beta barrel structures. the amino acids that face the outside of the barrel have what kind of side chains?

hydrophobic

the tails of phospholipids are:

hydrophobic

multipass transmembrane proteins can form pores across the lipid bilayer. the structure of one such channel is shown in the diagram. in this figure, the areas in red are:

the hydrophilic side chains of the transmembrane alpha helices

which portion of a membrane phospholipid faces the outside of the membrane?

the head

In most animal cells, which ion can move through "leak" channels?

K

Ion gradients are often used to drive the active transport of other molecules across a cell membrane. Based on this table, which ion would not likely be useful for driving coupled transport?

Mg2+

why do phospholipids form bilayers in water?

the hydrophilic head is attracted to water while the hydrophobic tail shuns water

in one second, a phospholipid molecule in an artificial bilayer may diffuse as far as what distance?

2 microns

which of these membrane-associated protein structures has never been found in a cell membrane?

5 (curly on right end)

how thick is the plasma membrane?

50 atoms

in a typical animal cell, approximately how much of the mass of the plasma membrane is constituted by proteins?

50%

which of the following statements describes the resting membrane potential of a neuron?

a state in which the flow of positive and negative ions across the plasma membrane is precisely balanced

which is not found in a cell membrane?

DNA

the plasma membrane is not involved in:

DNA replication

in fungi, plants, and bacteria, which pump helps to drive the import of solutes?

H pumps

the movement of an ion against its concentration gradient is called?

active transport

which of the following ions has a larger electrochemical gradient across a cells plasma membrane?

Na

lipid bilayers are highly impermeable to:

Na and Cl

when the glucose- Na symport protein is in its outward-open state, which is more likely to occur?

Na binds to binding site

which of the following statements is true?

Na is the most plentiful positively charged ion outside the cell, while K is most plentiful inside the cell

the Na pump in the plasma membrane of animal cells uses energy from ATP hydrolysis to pump sodium and potassium ions against their electrochemical gradients. in which direction are the ions pumped across the membrane?

Na out K in

the inside of a cell:

is slightly more negative than the outside of a cell

shown is a schematic diagram of a membrane phospholipid. which segment could carry a positive charge?

a (top)

what do carbohydrates attached to cell-surface proteins and lipids provide for a cell?

a distinctive identity in cell-cell recognition, a slimy coat that prevents cells from sticking from one another, protection from mechanical and chemical damage

which FRAP curve would show a more rapid recovery of fluorescense: one obtained from a cell membrane that contained a large proportion of saturated fatty acids or one from a cell membrane with a large proportion of unsaturated fatty acids?

a membrane containing a larger proportion of unsaturated fatty acids would show a more rapid recovery in a FRAP study

an electrochemical gradient has a chemical component and an electrical component. which of the following will have the largest electrochemical gradient?

a positively charged ion, such as Na, at high concentration outside the cell

which is not an integral membrane protein?

a protein attached to the membrane by noncovalent interactions with other membrane proteins

in general, which of the following will diffuse across a lipid bilayer most rapidly?

a small hydrophobic molecule

treatment of this membrane with a detergent like SDS would release which protein or proteins from the bilayer?

all of the proteins

the entire phospholipid molecule is:

amphipathic

the oils found in plant seeds and the fats found in an animals fat (or adipose) cells:

are hydrophobic

treatment of this membrane with phospholipase c would release which protein or proteins from the bilayer?

b

shown is a schematic diagram of a membrane phospholipid. which segment could carry a negative charge?

b (second)

why do cells lack membrane transport proteins that are specific for the movement of O2?

because oxygen dissolves readily in lipid bilayers

animals exploit the phospholipid asymmetry of their plasma membrane to distinguish between live cells and dead ones. when animal cells undergo a form of programmed cell death called apoptosis, phosphatidylserine- a phospholipid that is normally confined to the cytosolic monolayer of the plasma membrane-rapidly translocates to the extracellular, outer monolayer. the presence of phosphatidylserine on the cell surface serves as a signal that helps direct the rapid removal of the dead cell. how might a cell engineer this phospholipid redistribution?

by activating a scramblase and inactivating a flippase in the plasma membrane

When Na+ channels are opened in an animal cell, what happens to the membrane potential?

it becomes less negative inside the cell

The diffusion of an integral membrane protein is studied by fluorescence recovery after photobleaching (FRAP). In this procedure, the protein of interest is labeled with a fluorescent marker, and the fluorescence in a small patch of membrane is then irreversibly "bleached" by a pulse of light from a focused laser. The time it takes for fluorescence to return to the bleached membrane patch provides a measure of how rapidly unbleached, fluorescently labeled proteins diffuse through the bilayer into the area. This "recovery" is plotted on a curve that shows fluorescence over time. For one protein, which acts as a receptor for an extracellular signal molecule, stimulation by its signal ligand causes the receptor to interact with other membrane proteins, forming a large protein signaling complex. Shown first is the FRAP result for the unstimulated receptor. Which curve would most likely represent the behavior of the receptor once it has been activated by its signal molecule?

c

The movement of an individual protein in a cell membrane can be followed using a technique called single-particle tracking. In the diagram of the red blood cell cortex shown in Figure 1, actin proteins would show which of the three types of movement in Figure 2?

c

to study the structure of a particular membrane protein, the target protein is usually removed from the membrane and separated from other membrane proteins. shown are three different proteins associated with the cell membrane. treatment of this membrane with high salt would release which protein or proteins from the bilayer?

c

which of the following statements is true about the concentration of calcium ions in cells?

calcium levels are kept low in the cytosol compared to outside the cell

the shape of a cell and the mechanical properties of its plasma membrane are determined by a meshwork of fibrous proteins called the:

cell cortex

which of the following form tiny hydrophilic pores in the membrane through which solutes can pass by diffusion?

channels

how do transporters and channels select which solutes they help move across the membrane?

channels discriminate between solutes mainly on the basis of size and electric charge; transporters bind their solutes with great specificity in the same way an enzyme binds its substrate

how does cholesterol in animal cell membranes affect the bilayer?

cholesterol tends to stiffen the bilayer

which is not a mechanism for restricting the movement of proteins in the plasma membrane?

coating proteins with carbohydrates

The Na+ electrochemical gradient established by the Na+ pumps in the plasma membrane allows animal cells to:

control the pH, import nutrients, propagate electrical signals, stimulate muscle cell contraction (all of the above)

which organelle is important for controlling the concentration of calcium ions in the cytosol?

endoplasmic reticulum

on what side of the plasma membrane are the carbohydrate chains of glycoproteins, proteoglycans, and glycolipids located?

external (noncytosolic) side

A symport protein would function as an antiport protein if its orientation in the membrane were reversed.

false

When a muscle cell is stimulated, Ca2+ pumps in the sarcoplasmic reticulum use the energy of ATP to move Ca2+ into the cytosol, stimulating the cell to contract.

false

all of the carbohydrates in the plasma membrane face the cell exterior, and the carbohydrates on internal cell membranes face the cytosol

false

an ion channel undergoes conformational changes with each ion it passes.

false

human red blood cells contain no internal membranes other than the nuclear membrane

false

the glucose- Na symport protein uses the electrochemical Na gradient to drive the active transport of glucose into the cell. once this transporter has bound both Na and glucose, it preferentially opens toward the cytosol, where it releases both solutes.

false

water passes through the cell membrane only through specialized channels called aquaporins.

false

which of the following is not a function of plasma membrane proteins?

generate the energy required for lipids to diffuse through the membrane

organisms that live in cold climates adapt to low temperatures by:

increasing the amounts of unsaturated fatty acids in their membranes to help keep their membranes fluid

which of the following statements is true?

inside the cell, the quantity of positively charged ions is almost equal to the quantity of negatively charged ions

When an individual ion channel is stimulated to open (for example, by the binding of a neurotransmitter), what is the typical activity of the ion channel?

it continues to flicker between open and closed states, but spends more time open while the neurotransmitter is bound

which is not true of the molecule whose structural formula is shown?

it is found in the membranes of virtually all living cells

which of the following accurately describes the role of the Na pump?

it maintains a higher Na concentration outside the cell

in passive transport, the net movement of a charged solute across the membrane is determined by:

its electrochemical gradient

a functionally specialized region of a cell membrane, typically characterized by the presence of specific proteins is called a:

membrane domain

the voltage difference across a membrane of a cell is called the:

membrane potential

which of the following would be deterred from entering an ion channel with a negatively charged lining?

negatively charged ions

treating this membrane with a lectin would release which protein or proteins from the bilayer?

none of the proteins

sodium ions, oxygen, and glucose pass directly through lipid bilayers at dramatically different rates. which of the following choices presents the correct order, from fastest to slowest?

oxygen, glucose, sodium ions

the movement of an ion down its concentration gradient is called:

passive transport

which is the most abundant phospholipid in animal cell membranes?

phosphatidylcholine

which statement about phospholipids and detergents are not true?

phospholipids are amphipathic, whereas detergents are hydrophobic

which of the following will produce the most fluid lipid bilayer?

phospholipids with tails of 18 carbon atoms and 2 double bonds

in eukaryotic cells, new phospholipids are manufactured by enzymes bound to:

the cytosolic face of the endoplasmic reticulum

all other factors being equal, which type of solute does a cell tend to pull inside?

positively charged solutes

when grown at higher temperatures, bacteria and yeast maintain an optimal membrane fluidity by:

producing membrane lipids with tails that are longer and contain fewer double bonds

bacteriorhodopsin is a membrane transport protein that uses sunlight to do what?

pump H out of the cell to generate a H gradient across the plasma membrane

margarine is made from vegetable oils in which the hydrocarbon tails have had what treatment?

removing the double bonds by adding hydrogen (which converts double to single bonds)

what type of enzyme moves randomly selected phospholipids from one monolayer of a lipid bilayer to another?

scramblase

which of the following statements is not true regarding active transport by transmembrane pumps?

some solutes are transported across the membrane in tandem with another molecule, both moving from lower concentration to higher concentration

which term describes a coupled transporter that moves both solutes in the same direction across a membrane?

symport

Fluorescence recovery after photobleaching (FRAP) is used to monitor the movement of fluorescently labeled molecules within the plane of a cell membrane. The molecules labeled are often proteins, but can also be lipids. How would the curve that represents FRAP for labeled proteins compare to the curve representing labeled lipids?

the FRAP curve for lipids would show very rapid recovery to initial levels of fluorescence

The epithelial cells that line the gut have glucose-Na+ symport proteins that actively take up glucose from the lumen of the gut after a meal, creating a high glucose concentration in the cytosol. How do these cells release that glucose for use by other tissues in the body?

the cells have glucose uniports in their plasma membrane

the direction that glucose is transported across the membrane is determined by:

the concentration gradient

when glucose moves across a phospholipid bilayer by passive transport, which factor determines the direction of its transport?

the concentrations of glucose on either side of the membrane

which of the following inhibits inorganic ions, like Na and Cl, from passing through a lipid bilayer?

the hydrophobic interior of the lipid bilayer

which of the following requires an input of energy to occur?

the movement of a solute from a region of lower concentration on one side of a membrane to a region of higher concentration on the other side

osmosis can be described as:

the movement of water from an area of low solute concentration to an area of high solute concentration

when the transport vesicle shown here fuses with the plasma membrane, which monolayer will face the cell cytosol?

the orange monolayer

when a vesicle fuses with the plasma membrane, the monolayer that was facing the inside of the vesicle will face:

the outside of the cell

in the alpha helices of transmembrane proteins, the hydrophobic side chains are facing:

the outside of the membrane-spanning helix

in bacteria, the transport of many nutrients, including sugar and amino acids, is driven by the electrochemical H gradient across the plasma membrane. In ecoli, for example, a H- lactose symporter mediates the active transport of the sugar lactose into the cell. given what you know about coupled transport, which is likely true of the H- lactose symporter?

the transporter oscillates randomly between states in which it is open to either the extracellular space or the cytosol

in a patch of animal cell membrane about 10um2 in area, which will be true?

there will be more lipids than proteins

what is typically true of ion channels?

they are gated

which of the following mechanisms prevents osmotic swelling in plant cells?

tough cell walls

which type of membrane transport protein can perform either passive or active transport?

transporters

given enough time, virtually any molecule will diffuse across a lipid bilayer.

true

the glucose-Na symport in epi cells uses the electrochemical gradient of Na to draw glucose into the cell.

true

which has a larger number of double bonds?

vegetable oil

in one experiment, investigators create a liposome- a vesicle made of phospholipids- that contains a solution of 1 mM glucose and 1 mM sodium chloride. if this vesicle were placed in a beaker of distilled water, what would happen the fastest?

water would diffuse in

in a lipid bilayer, lipids rapidly diffuse:

within the plane of their own monolayer