CHAPTER 4

Question 1

extracellular fluid contains a
large amount of

Answer 1

SODIUM, and also chlorine ions

Question 2

but only a small amount of

Answer 2

potasium

Question 2

the intracellular fluid are considerably greater than those in the extracellular fluid

Answer 2

phosphates and proteins

Question 3

Most of these penetrating proteins therefore, can function as

Answer 3

transport proteins

Question 4

Some have watery spaces all
the way through the molecule and allow free movement of water, as well as selected ions or molecules; these are
called

Answer 4

channel proteins

Question 5

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

Answer 5

Diffusion

Question 5

are usually highly selective for the types of molecules or ions that are allowed to
cross the membrane.

Answer 5

Both the channel proteins and the carrier proteins

Question 5

bind with molecules or ions that are to be transported;
conformational changes in the protein molecules then move the substances through the interstices of the protein to the other side of the membrane.

Answer 5

called carrier proteins

Question 5

Transport through the cell membrane, either directly through the lipid bilayer or through the proteins, occurs by one of two basic processes:

Answer 5

Diffusion or Active transport

Question 6

The energy that causes diffusion is the energy of the

Answer 6

Normal kinetics motion of matter.

Question 7

Means movement of ions
or other substances across the membrane in combination with a carrier protein in such a way that the carrier protein causes the substance to move against an energy gradient, such as from a low-concentration state to a high concentration state.

Answer 7

Active transport

Question 8

This continual movement of molecules among one another in liquids or in gases is called

Answer 8

diffusion

Question 9

Diffusion through the cell membrane is divided into two subtypes called

Answer 9

Simple diffusion and facilitated diffusion

Question 10

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

Answer 10

Simple diffusion

Question 11

The rate of diffusion is determined by the amount of substance available,

Answer 11

The velocity of kinetic motion, and the number and sizes of openings in the membrane through which the molecules or ions can move.

Question 12

Requires interaction of a carrier
protein.
The carrier protein aids passage of the molecules or ions through the membrane by binding chemically with them and shuttling them through the membrane in
this form.

Answer 12

Facilitated diffusion

Question 13

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

Answer 13

1. Through the interstices of the lipid bilayer if the diffusing substance is lipid soluble.
2. Through watery channels that penetrates all the way of some the large transport proteins.

Question 14

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

Answer 14

Lipid solubility

Question 15

Are high, so all these can dissolve directly in
the lipid bilayer and diffuse through the cell membrane in the same manner that diffusion of water solutes occurs in a watery solution.

Answer 15

The lipid solubilities of oxygen, nitrogen, carbon dioxide, and alcohols

Question 16

water is highly insoluble in the membrane lipids, it readily passes through channels in protein molecules that penetrate all the way through the membrane.

Question 16

water is highly insoluble in the membrane lipids, it readily passes through channels in protein molecules that penetrate all the way through the membrane is

Answer 16

astounding

Question 17

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

Answer 17

Pores

Question 17

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

Answer 17

aquaporins or water channels

Question 18

Aquaporins have a narrow pore that permits water molecules to diffuse through the membrane in single file

Question 19

The protein channels are distinguished by two important characteristics:

Answer 19

(1) They are often selectively permeable to certain substances, and (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 to the channel proteins (ligand-gated channels)

Question 20

Permit passage of potassium ions across the cell membrane about 1000 times more readily than they permit passage of sodium ions.

Answer 20

Potassium channels

Question 20

were found to have a tetrameric structure consisting of four identical protein subunits surrounding a central pore

Answer 20

Potassium channels

Question 20

At the top of the channel pore are pore loops that form a narrow

Answer 20

selectivity filter

Question 20

Lining the selectivity filter are

Answer 20

carbonyl oxygens

Question 21

One of the most important of the protein channels, the is only 0.3 by 0.5 nanometer in diameter.

Answer 21

sodium channel

Question 21

but more important, the inner surfaces of this channel are lined with amino acids that are

Answer 21

strongly negatively charged

Question 22

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

Answer 22

1. Voltage gating 2. Chemical (ligand) gating

Question 23

This causes a conformational or chemical bonding change in the protein molecule that opens or closes the gate. This is called

Answer 23

Chemical gating or Ligand gating

Question 24

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

Answer 24

Acetylcholine channel

Question 25

This gate is exceedingly important for the transmission of nerve signals from one nerve cell to another and from nerve cells to muscle cells to cause muscle contraction.

Question 26

Facilitated diffusion is also called

Answer 26

carrier-mediated diffusion

Question 27

because a substance transported in this manner diffuses through the membrane using a specific carrier protein to help. That is, the

Answer 27

Carrier facilitates diffusion

Question 28

Although the rate of simple diffusion through an open channel increases proportionately with the concentration of the diffusing substance in facilitated diffusion the rate of diffusion approaches a maximum, called

Answer 28

Vmax

Question 29

Among the most important substances that cross cell membranes by facilitated diffusion are

Answer 29

Glucose and most of the amino acids.

Question 30

, is activated by insulin, which can increase the rate of facilitated diffusion of glucose as much as 10-fold to 20-fold in insulin-sensitive tissues.

Answer 30

glucose transporter 4 (GLUT4),

Question 31

Co is concentration outside

Question 32

Ci is concentration inside

Question 33

At normal body temperature (37°C), the electrical difference that will balance a given concentration difference of univalent ions—such as sodium (Na+) ions—can be determined from the following formula, called the

Answer 33

Nernst equation

Question 33

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

Answer 33

Pressure

Question 34

By far the most abundant substance that diffuses through the cell membrane is

Answer 34

water

Question 35

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

Answer 35

osmosis

Question 36

The exact amount of pressure required to stop osmosis is called the

Answer 36

Osmotic pressure

Question 37

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

Answer 37

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

Question 38

To express the concentration of a solution in terms of numbers of particles, the unit called the

Answer 38

osmole

Question 39

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

Answer 39

Osmolarity

Question 39

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 39

active transport

Question 39

Active transport is divided into two types according to the source of the energy used to cause the transport:

Answer 39

1. primary active transport 2. secondary active transport

Question 40

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

Answer 40

Primary active transport

Question 41

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

Answer 41

secondary active transport

Question 41

responsible for maintaining the sodium and potassium concentration differences across the cell membrane, as well as for establishing a negative electrical voltage inside the cells.

Answer 41

pump

Question 42

is a complex of two separate globular proteins:

Answer 42

carrier protein

Question 43

a larger one called the " α subunit" with a molecular weight of about 100,000, and a smaller one called the "β subunit"

Question 44

1. It has three receptor sites for binding sodium ions on the 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 sodium binding sites has ATPase activity

Question 44

One of the most important functions of the Na+-K+ pump is to control the v

Answer 44

volume of each cell

Question 45

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

Question 46

The normal mechanism for preventing this is the

Answer 46

Na+-K+ pump

Question 46

Another important primary active transport mechanism is the

Answer 46

calcium pump

Question 47

Are normally maintained at extremely low concentration in the intracellular cytosol of virtually all cells in the body, at a concentration about 10,000 times less than that in the extracellular fluid.

Answer 47

Calcium ions

Question 48

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

Answer 48

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

Question 48

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

Answer 48

Deep-lying parietal cells

Question 49

r. Under appropriate conditions, this diffusion energy of sodium can pull other substances along with the sodium through the cell membrane. This phenomenon is called c

Answer 49

co-transport

Question 50

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

Answer 50

counter-transport

Question 51

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

Answer 51

Sodium-glucose co-transporters

Question 52

occurs in the same manner as for glucose, except that it uses a different set of transport proteins

Answer 52

Sodium co-transport of the amino acids

Question 53

Five amino acid transport proteins have been identified, each of which is responsible for transporting one subset of amino acids with specific molecular characteristics

Question 54

Sodium co-transport of glucose and amino acids occurs especially through the

Answer 54

epithelial cells of the intestinal tract and the renal tubules of the kidneys

Question 54

Two especially important counter-transport mechanisms (transport in a direction opposite to the primary ion) are

Answer 54

1. sodium-calcium counter-transport 2. sodium-hydrogen counter-transport

Question 55

occurs in several tissues

Answer 55

Sodium-hydrogen counter-transport

Question 55

Sodium-calcium counter-transport and sodium-hydrogen counter-transport

Answer 55

Sodium-calcium counter-transport

Question 55

An especially important example is in the --- of the kidneys, where sodium ions move from the lumen of the tubule to the interior of the tubular cell, while hydrogen ions are counter-transported into the tubule lumen.

Answer 55

proximal tubules

Question 55

At many places in the body, substances must be transported all the way through a cellular sheet instead of simply through the cell membrane. Transport of this type occurs through the:

Answer 55

(1) intestinal epithelium (2) epithelium of the renal tubules (3) epithelium of all exocrine glands, (4) epithelium of the gallbladder, and (5) membrane of the choroid plexus of the brain and other membranes.

Question 56

This figure shows that the epithelial cells are connected together tightly at the luminal pole by means of junctions called

Answer 56

“kisses"

Question 56

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

Answer 56

(1) active transport through the cell membrane on one side of the transporting cells in the sheet, and then (2) either simple diffusion or facilitated diffusion through the membrane on the opposite side of the cell.