5 Membrane Transport and Cell Signaling

Question 1

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

Answer 1

phospholipids and proteins

Question 2

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

Answer 2

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

Question 3

The presence of cholesterol in the plasma membranes of some animals

Answer 3

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

Question 4

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

Answer 4

They can move laterally along the plane of the membrane.

Question 5

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?

Answer 5

by increasing the percentage of unsaturated phospholipids in the membrane

Question 6

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

Answer 6

amphipathic, with at least one hydrophobic region.

Question 7

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

Answer 7

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

Question 8

Which of the following is true of integral membrane proteins?

Answer 8

They are usually transmembrane proteins.

Question 9

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

Answer 9

to mediate cell-to-cell recognition.

Question 10

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

Answer 10

a transmembrane protein.

Question 11

Which of these are not embedded in the hydrophobic portion of the lipid bilayer at all?
A) transmembrane proteins
B) integral proteins
C) peripheral proteins
D) integrins
E) glycoproteins

Answer 11

peripheral proteins

Question 12

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

Answer 12

small and hydrophobic

Question 13

Which of the following is a characteristic feature of a carrier protein in a plasma membrane?

Answer 13

It exhibits a specificity for a particular type of molecule.

Question 14

Nitrous oxide gas molecules diffusing across a cell’s plasma membrane is an example of

Answer 14

diffusion across the lipid bilayer.

Question 15

Which of the following statements is correct about diffusion?

Answer 15

It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.

Question 16

Water passes quickly through cell membranes because

Answer 16

it moves through aquaporins in the membrane.

Question 17

Mammalian blood contains the equivalent of 0.15 M NaCl. Seawater contains the equivalent of 0.45 M NaCl. What will happen if red blood cells are transferred to seawater?

Answer 17

Water will leave the cells, causing them to shrivel and collapse.

Question 18

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

Answer 18

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

Question 19

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

Answer 19

The cell will become turgid.

Question 20

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

Answer 20

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

Question 21

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?

Answer 21

facilitated diffusion

Question 22

What is the voltage across a membrane called?

Answer 22

membrane potential

Question 23

The sodium-potassium pump is called an electrogenic pump because it

Answer 23

contributes to the membrane potential.

Question 24

The movement of potassium into an animal cell requires

Answer 24

an energy source such as ATP.

Question 25

Ions diffuse across membranes through specific ion channels

Answer 25

down their electrochemical gradients.

Question 26

Which of the following would increase the electrochemical potential across a membrane?

Answer 26

a proton pump

Question 27

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?

Answer 27

It will be on the cytoplasmic side of the ER.

Question 28

An organism with a cell wall would most likely be unable to take in materials through

Answer 28

phagocytosis.

Question 29

White blood cells engulf bacteria through what process?

Answer 29

phagocytosis

Question 30

The difference between pinocytosis and receptor-mediated endocytosis is that

Answer 30

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

Question 31

In receptor-mediated endocytosis, receptor molecules initially project to the outside of the cell. Where do they end up after endocytosis?

Answer 31

on the inside surface of the vesicle

Question 32

A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in

Answer 32

lysosomes.

Question 33

What role does a transcription factor play in a signal transduction pathway?

Answer 33

By binding to DNA it triggers the transcription of a specific gene.

Question 34

Which of the following is a substance that acts at a long distance from the site at which it is secreted?

Answer 34

hormone

Question 35

To what does the term “ligand” refer in cell biology?

Answer 35

any small molecule that can bind in a specific manner to a larger one

Question 36

Why are there often so many steps between the original signal event and the cell’s response?

Answer 36

Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses.

Question 37

Active and passive transport of solutes across a membrane typically differ in which of the following ways?

Answer 37

Active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy.

Question 38

Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because __________.

Answer 38

they amplify the original signal manyfold