Exam 3: Biological Membranes and Transport

Question 1

What does the “mosaic model” of biological membranes propose?

Answer 1

“A proposed model that claims that lipids form a viscous, two-dimensional solvent into which proteins are inserted and integrated more deeply or less deeply.”

Question 2

What are characteristics of integral proteins?

Answer 2

Integral proteins are firmly associated with the membrane and can be found throughout the entire bilayer.

Question 3

What are characteristics of peripheral proteins?

Answer 3

Peripheral proteins are weakly associated with the surface of the bilayer. They are easily removed and soluble.

Question 4

(True or False) Outer and inner leaflets have different lipid compositions.

Answer 4

True.

Question 5

Name the three forms of lipids that make up the lipid bilayer.

Answer 5

Phospholipids, sphingolipids, and sterols.

Question 6

How are the leaflets of the bilayer different in their composition?

Answer 6

Different organisms, tissues, and organelles all have different ratios of lipids to proteins, types of phospholipids, and abundances of sterols.

Question 7

What sorts of changes can cause a peripheral protein to dissociate from the membrane?

Answer 7

Changes in salt concentration or pH.

Question 8

What is required to remove integral proteins from the membrane?

Answer 8

A detergent to disrupt the membrane.

Question 9

On a hydropothy index, does a positive value denote a hydrophobic residue or a hydrophilic residue?

Answer 9

A positive value denotes a hydrophobic residue.

Question 10

Typ and Trp are largely found clustered where in an integral protein?

Answer 10

Typ and Trp are largely found clustered at the polar/nonpolar interfaces of the membrane.

Question 11

Charged residues of an integral protein are found where?

Answer 11

In aqueous domains.

Question 12

If a protein has a segment of ____ residues, it is a membrane spanning protein.

Answer 12

20.

Question 13

Lateral diffusion within a leaflet is very _____.

a. fast
b. slow

Answer 13

a. fast

Question 14

Transverse diffusion across leaflets can be induced by a ______ enzyme.

Answer 14

flippase

Question 15

What are two methods that flippases may cause transverse diffusion across leaflets?

Answer 15

Energy utilization of ATP or by moving two lipids (one lipid from either side of the membrane) at once.

Question 16

What are traits that a molecule must have to pass through the bilayer without a transporter?

Answer 16

It must be very small and nonpolar.

Question 17

Why is there a large energy barrier to be overcome by polar molecules that prevents them from passively diffusing.

Answer 17

Polar molecules must be dissolved, and so the interactions between the bonds must be broken, creating an energy barrier.

Question 18

Primary active transport moves ___ molecule(s) against their gradient using ______.

Answer 18

1, ATP

Question 19

Secondary active transport moves ___ molecule(s) against their gradient using _____.

Answer 19

2, an electrochemical gradient (symport or antiport)

Question 20

Define the variables in the following equation:

ΔG_t = RTln (C_2/C_1 ) + zFΔψ

Answer 20

ΔG_t: The relative free-energy change

R: Gas constant (8.314 J/mol·K)

T: Temperature in kelvin

C_2/C_1: Concentration 2 and concentration 1

z: Charge of the molecule

F: The Faraday constant (95.6 kJ/molV)

ψ: The charge of the membrane in the direction of movement