Chapter 4: Transport of substances through cell membranes

Question 1

not miscible with either the extracellular fluid or the intracellular fluid.

Answer 1

lipid bilayer

Question 2

it constitutes a barrier against movement of water molecules and water-soluble substances between the extracellular and intracellular fluid compartments.

Answer 2

lipid bilayer

Question 3

contains alarge amount of sodium but only a small amount of potassium

Answer 3

extracellular fluid

Question 4

watery spaces all the way through the molecules and allow free movement of water, as well as selected ions or molecules

Answer 4

channel proteins or carrier proteins

Question 5

bind with molecules or ions that are to be transported;conformational changes in the proteinmolecules thenmove the substances through theninterstices of the proteinto the other side of the
membrane

Answer 5

carrier proteins

Question 6

Transport through the cell membrane, either directly through thelipid bilayer or through the proteins, occurs by one of twobasic processes

Answer 6

diffusion or active transport

Question 7

means random molecular movement of substances molecule by molecule either through intermolecular spaces in the membrane or in combination with a carrier protein

Answer 7

diffusion

Question 8

The energy that causes diffusion is the energy
of the?

Answer 8

normal kinetic motion of matter

Question 9

movement of ions or other substances across the membrane in combination with a carrier protein in such a
way that the carrier protein

Answer 9

active transport

Question 10

Motion of these particles is what
physicists call?

Answer 10

“heat”
—the greater the motion the higher the temperature—and the motionnever ceases
under any condition except at absolute zero temperature

Question 11

continual movement of molecules among one another in liquids or in gases

Answer 11

diffusion

Question 12

Diffusion through the cell membrane is divided into two subtypes called?

Answer 12

simple diffusion and facilitated diffusion

Question 13

means that kinetic movement of molecules or ions occurs through a membrane openingor through intermolecular spaces without any interaction with
carrier proteins in the membrane

Answer 13

simple diffusion

Question 14

requires interaction of a
carrier protein

Answer 14

facilitated diffusion

Question 15

Simple diffusion can occur through the cell
membrane by two pathways:

Answer 15

(1) through the interstices of the lipid bilayer if the diffusing substance is lipid soluble
(2) through watery
channels that penetrate all the waythrough some
of the large transport proteins

Question 16

one of the most important
factors that determines how rapidly a substance
diffuses through the lipid bilayer is the?

Answer 16

lipid solubility

Question 17

can dissolve directly in
the lipid bilayer and diffuse through the cell membrane inthe same manner that diffusion of water solutes occurs in awatery solution

Answer 17

oxygen
nitrogen
carbon dioxide
alcohols

Question 18

highly insoluble in the membrane lipids

Answer 18

water

Question 19

composed of integral cell membrane proteins that form open tubes through the
membrane and are always open

Answer 19

pores

Question 20

permit rapid passage of water through cell membranes but
exclude other molecules

Answer 20

aquaporins or water channels

Question 21

The protein channels are distinguished by two important characteristics:

Answer 21

(1) They are often selectively permeable to certain substances
(2)
many of the channels can be opened or closed by
gates that are regulated by electrical signals
(voltage-gated channels) or chemicals that bind tothe channel proteins (ligand-gated channels).

Question 22

permit passage of potassium ions across the cell membrane about 1000
times more readilythan they permit passage of sodium ions

Answer 22

potassium channels

Question 23

What is the mechanism for this remarkable ion selectivity?

Answer 23

when the structure of a bacterial potassium channel was determined by x-ray crystallography

Question 24

Potassium channels were found to have a

Answer 24

tetrameric

Question 25

Even though water is highly insoluble in the membrane lipids, it readily passes

Answer 25

through channels in protein molecules

Question 26

the total amount ofwater that diffuses in each direction through the red cell membrane during each second is about _________ as great as the volume of the red cell itself

Answer 26

100 times

Question 27

the diameter of the urea molecule is only ________ greater than that of water, yet its penetration through the cell membrane pores is about 1000 times lessthan that of water

Answer 27

20 percent

Question 28

structure consisting of four identical protein subunits surrounding a central pore

Question 29

At the top of the channel pore are

Answer 29

pore loops

Question 30

Lining the selectivity filter are?

Answer 30

carbonyl oxygens

Question 31

Different selectivity filters for the various ion channels are believed to determine, in large part, the specificity of the channel for cations or anions or for particular ions, such as _______, _______, ________ that gain access to the channels

Answer 31

Na, K, Ca

Question 32

one of the most important of the protein channels, only 0.3 by 0.5 nan- ometer in diameter, but more important, the inner surfaces of this channel are lined with amino acids that are strongly negatively charged

Answer 32

sodium channel

Question 33

strong negative charges can pull small dehydrated sodium ions into these channels, actually pulling the sodium ions away from their hydrating water molecules

Question 34

provides a means of controlling ion permeability of the channels.

Answer 34

gating of protein channels

Question 35

The opening and closing of gates are controlled in two principal ways:

Answer 35

° voltage gating ° Chemical (ligand) gating

Question 36

responds to the electrical potential across the cell membrane

Answer 36

voltage gating

Question 37

Some protein channel gatesare opened by the binding of a chemical substance (aligand) with the protein; this causes a conformationalorchemical bonding change in the protein molecule thatopens or closes the gate

Answer 37

chemical gating or ligand gating

Question 38

one of the most important instances of chemical gating is the effect of acetylcholine on the so called?

Answer 38

acetylcholine channel

Question 39

This gate is exceedingly important for the transmission of nerve signals from one nerve cell to another

Answer 39

chemical gating

Question 40

Facilitated diffusion is also called

Answer 40

carrier mediated diffusion

Question 41

using a specific carrier protein to help. That is, the carrier facilitates diffusion ofthe substance to the other side

Answer 41

facilitated diffusion

Question 42

Facilitated diffusion differs from simple diffusion in the following important way:

Answer 42

✓ increases proportionately with the concentration of the diffusing substance ✓ facilitated diffusion approaches a maximumrate called the Vmax

Question 43

in facilitated diffusion the rate of diffusion approaches a maximum

Answer 43

Vmax

Question 44

most important substances that cross cell membranes by facilitated diffusion are?

Answer 44

glucose and most of the amino acids

Question 45

in the case of glucose, at least five glucosetransporter molecules have been discovered in various tissues

Question 46

monosaccharides that have structures similar to that of glucose, including;

Answer 46

galactose and fructose

Question 47

one of these, glucose transporter 4 (GLUT4), is activated by?

Answer 47

insulin

Question 48

if an electrical potential is applied across the membrane the electrical charges of the ions cause them to move through the membrane even though no concentration difference exists to cause movement

Answer 48

nernst potential

Question 49

The positive charge attracts the negative ions, whereas the negative charge repels them

Answer 49

net diffusion

Question 50

The pressure is about ________ greater inside the capillary than outside

Answer 50

20mm Hg

Question 51

means the sum of all the forces of the different molecules striking a unit surface area at a given instant

Answer 51

pressure

Question 52

most abundant substance that diffuses through the cell membrane

Answer 52

water

Question 53

Enough water ordinarily diffuses in each direction through the red cell membrane per second to equal about __________ the volume of the cellitself

Answer 53

100 times

Question 54

process of net movement of water caused by a concentration difference of water

Answer 54

osmosis

Question 55

exact amount of pressure required to stop osmosis

Answer 55

osmotic pressure

Question 56

The osmotic pressure exerted by particles in a solution,whether they are molecules or ions, is determined by the

Answer 56

number of particles per unit volume of fluid, not bythe mass of the particles

Question 57

terms of numbers of particles, the unit called?

Answer 57

osmole

Question 58

normally body temperature

Answer 58

37°C

Question 59

can develop across a membrane, just as concentration differences for other substances can occur.

Answer 59

concentration difference to water

Question 60

process of net movement of water caused by a concentration difference of water is called

Answer 60

osmosis

Question 61

is the osmolar concentration expressed as osmoles per liter of solution rather than osmoles per kilogram of water

Answer 61

osmolarity

Question 62

When a cell membrane moves molecules or ions “uphill ” against a concentration gradient (or “uphill ” against an electrical or pressure gradient), the process is called

Answer 62

active transport

Question 63

the energy is derived directly from breakdown of adenosine triphosphate (ATP) or of some other high-energy phosphate compound

Answer 63

primary active transport

Question 64

the energy is derived secondarily from energy that has been stored inthe form of ionic concentration differences of secondary molecular or ionic substances between the two sidesof a cell membrane, created originally by primary active transport

Answer 64

secondary active transport

Question 65

Among the substances that are transported by primary active transport are;

Answer 65

° sodium ° potassium ° calcium ° hydrogen ° chloride

Question 66

The active transport mechanism that has been studied in greatest detail

Answer 66

sodium- potassium pump

Question 67

a transport process that pumps sodium ions outward through the cell membrane of all cells and at thesame time pumps potassium ions from the outside tothe inside

Answer 67

sodium-potassium pump

Question 68

This pump is responsible for maintaining the sodium and potassium concentration differences acrossthe cell membrane, as well as for establishing a negative electrical voltage inside the cells

Answer 68

sodium-potassium pump

Question 69

is a complex of two separate globular proteins

Answer 69

carrier proteins

Question 70

large, with a molecular weight of about 100,000

Answer 70

α subunit

Question 71

large, with a molecular weight of about 100,000

Answer 71

α subunit

Question 72

smaller,with a molecular weight of about 55, 000

Answer 72

B subunit

Question 73

the larger protein has three specific features that are important for the functioning of the pump:

Answer 73

1. It has three receptor sites for binding sodium ions onthe portion of the protein that protrudes to the inside of the cell. 2. It has two receptor sites for potassium ions on the outside. 3. The inside portion of this protein near the sodiumbinding sites has ATPase activity

Question 74

enzymes that catalyze the decomposition of ATP into ADP

Answer 74

ATPase

Question 75

Another important primary active transport mechanism

Answer 75

calcium pump

Question 76

are normally maintained at extremely low concentration in the intracellularcytosol of virtually all cells in the body, at a concentrationabout 10,000 times less than that in the extracellular fluid

Answer 76

calcium ions

Question 77

At two places in the body, primary active transport hydrogen ions is important;

Answer 77

1) gastric glands of the stomach (2) late distal tubules and cortical collecting ducts of the kidneys

Question 78

have the most potent primary active mechanism for transporting hydrogen ions of any part of the body.

Answer 78

parietal cells

Question 79

In the renal tubules are special __________in thelate distal tubules and cortical collecting ducts that alsotransport hydrogen ions by primary active transport

Answer 79

intercalated cells

Question 80

this diffusion energy of sodium can pull other substances along with the sodium through the cell membrane. This phenomenon is called?

Answer 80

co-transport

Question 81

co-transport is one form of?

Answer 81

secondary active transport

Question 82

sodium ions again attempt to diffuse to the interior of the cell because of their large concentration gradient

Answer 82

counter transport

Question 83

the conformational change takes place automatically, and the sodium and glucose are transported to the inside ofthe cell at the same time.

Answer 83

sodium-glucose co-transport

Question 84

especially important mechanisms in transporting glucose across renal and intestinal epithelial cells

Answer 84

sodium-glucose co-transport

Question 85

other important co-transport mechanisms in at least some cells include;

Answer 85

co-transport of chloride ions, iodine ions, iron ions, and urate ions

Question 86

Two especially important counter-transport mechanisms;

Answer 86

sodium-calcium counter-transport sodium-hydrogen counter-transport

Question 87

occurs through allor almost all cell membranes, with sodium ions moving tothe interior and calcium ions to the exterior, both bound to the same transport protein in a counter-transportmode

Answer 87

sodium-calcium counter-transport

Question 88

occurs in several tissues.

Answer 88

sodium-hydrogen counter transport

Question 89

Active Transport Through Cellular Sheets occurs through the?

Answer 89

✓ intestinal epithelium ✓ epithelium of the renal tubules ✓ epithelium of all exocrine glands ✓ epithelium of the gallbladder ✓ membrane of the choroid plexus of the brain

Question 90

The basic mechanism for transport of a substance through a cellular sheet

Answer 90

active transport

Question 91

the epithelial cells are connected together tightly at the luminal pole by means of junctions called?

Answer 91

kisses