2.10 CELL MEMBRANES

Question 1

_____also commonly called plasma membranes because they separate the cytoplasm (aqueous contents) of a cell from its surroundings. It is also defined as a lipid-based structure that separates a cell’s aqueous-based interior from the aqueous environment surrounding the cell. It also controls the movement of substances into and out of the cell

Answer 1

(Cell membrane)

Question 2

● Up to ____of the mass of a cell membrane is lipid material consisting primarily of the three types of membrane lipids just discussed: phospholipids, glycolipids, and cholesterol

Answer 2

80%

Question 2

● The keys to understanding the structural basis for a cell membrane are

Answer 2

{(1) the virtually insoluble nature of membrane lipids in water and (2) the “head and two tails” structure of phospholipids and sphingoglycolipids.}

Question 3

___ ● is a two-layer-thick structure of phospholipids and glycolipids in which the nonpolar tails of the lipids are in the middle of the structure and the polar heads are on the outside surfaces of the structure

Answer 3

LIPID BILAYER)

Question 4

● How thick is the lipid bilayer?

Answer 4

(six-billionths to nine-billionths of a meter thick—that is, 6 to 9 nanometers thick)

Question 5

● 3 DISTINCT PART OF THE LIPID BILAYER

Answer 5

( the exterior polar “heads,” the interior polar “heads,” and the central nonpolar “tails,”)

Question 6

● A lipid bilayer is held together by________, not by covalent bonds. This means each phospholipid or sphingolipid is free to diffuse laterally within the lipid bilayer

Answer 6

( intermolecular interactions)

Question 7

● Cholesterol molecules are also components of cell membranes. They regulate___________. Because of their compact shape. Within the membrane, the cholesterol molecule orientation is “______” to the outside

Answer 7

the hydroxyl group) and “______” to the inside (the steroid ring structure with its attached alkyl groups). [MEMBRANE RIGIDITY; head; TAIL]

Question 8

● There are two general types of membrane proteins

Answer 8

integral and peripheral

Question 9

● is a membrane protein that penetrates the cell membrane. Some membrane proteins penetrate only partially through the lipid bilayer, whereas others go completely from one side to the other side of the lipid bilayer

Answer 9

INTEGRAL MEMBRANE PROTEIN)

Question 10

● a nonpenetrating membrane protein located on the surface of the cell membrane.

Answer 10

(PERIPHERAL MEMBRANE PROTEIN)

Question 11

● _____________rather than chemical bonds govern the interactions between membrane proteins and the lipid bilayer

Answer 11

(Intermolecular forces)

Question 12

● Three common transport mechanisms exist by which molecules can enter and leave cells. They are

Answer 12

passive transport, facilitated transport, and active transport)

Question 13

● is the transport process in which a substance moves across a cell membrane by diffusion from a region of higher concentration to a region of lower concentration without the expenditure of any cellular energy. Only a few types of molecules, including O2, N2, H2O, urea, and ethanol, can cross membranes in this manner

Answer 13

(Passive transport)

Question 14

● what molecules can cross the membrane in a passive transport

Answer 14

O2, N2, H2O, urea, and ethanol)

Question 15

● is the transport process in which a substance moves across a cell membrane, with the aid of membrane proteins, from a region of higher concentration to a region of lower concentration without the expenditure of cellular energy. The specific protein molecules involved in the process are called carriers or transporters.

Answer 15

Facilitated Transport)

Question 16

● What molecules can cross the membrane in facilitated transport

Answer 16

Glucose, chloride ion, and bicarbonate ion)

Question 17

● Proteins involved in active transport are called “_______,” because they require energy much as a water pump requires energy in order to function

Answer 17

pumps

Question 17

● is the transport process in which a substance moves across a cell membrane, with the aid of membrane proteins, against a concentration gradient with the expenditure of cellular energy

Answer 17

Active transport

Question 18

● Why is there a need for energy in an active transport?

Answer 18

The need for energy expenditure is related to the molecules moving against a concentration gradient—from lower to higher concentration)

Question 19

● Why is there a need for active transport?

Answer 19

It is essential to life processes to have some solutes “permanently” at different concentrations on the two sides of a membrane, a situation contrary to the natural tendency (osmosis) to establish equal concentrations on both sides of a membrane. Hence the need for active transport.)

Question 20

● What molecules can cross the membrane during active transport

Answer 20

Sodium, potassium, and hydronium ion)

Question 21

1. The exterior surface positions in a lipid bilayer are occupied by?

Answer 21

• hydrophilic entities

Question 22

2. Which of the following polarity-based descriptions is correct for the interior of a lipid bilayer?

Answer 22

• contains nonpolar tails

Question 23

3. The biochemical function of the cholesterol present in cell membranes is?

Answer 23

• regulate membrane fluidity

Question 24

4. Which of the following membrane transport mechanism requires both the aid of proteins and the expenditure of energy?

Answer 24

• Active transport