3.2 - The Cell Membrane and Transport

Question 1

How much of the genome codes for membrane proteins?

Answer 1

1/3 of the genome

Question 2

What are the two main types of membrane proteins

Answer 2

(1) Integral proteins

(2) Peripheral proteins

Question 3

What are integral membrane proteins?

Answer 3

Integral membrane proteins are permanently attached to the membrane. They are embedded within the protein layer and cannot be removed easily. Integral proteins float rather freely within the bilayer.

Question 4

What is the typical type of integral protein?

Answer 4

Transmembrane proteins which extend through the lipid bilayer so that one end is in contact with the outside of the cell while the other is in contact with the interior

Question 5

Which part of integral protein is hydrophobic and which part is hydrophilic?

Answer 5

The portion of the protein in the hydrophobic region is hydrophobic whilst the extended parts of the protein are hydrophilic.

Question 6

What are peripheral membrane proteins?

Answer 6

Peripheral membrane proteins are temporarily attached either to the lipid bilayer or to integral proteins through a combination of hydrophobic, electrostatic and other non-covalent interactions. They are easily seperable and are less mobile than integral proteins

Question 7

Which between integral and peripheral proteins can be post-translationally modified?

Answer 7

Both

Question 8

What are some types of membrane proteins?

Answer 8

(1) Membrane proteins
(2) Transport proteins
(3) Enzymes
(4) Cell adhesion molecules
(5) Structural support proteins

Question 9

How does ATP synthase work?

Answer 9

There are a lot of protons in the inner membrane space of mitochondria. These protons flow through ATP synthase. Since protons are flowing down their concentration gradient e free energy released from their transport will lead to the rotation of a c ring in the ATP synthase. This drives the rotation of the gamma subunit which rotates beta modules. This generates 3 ATP.

Question 10

What are the two types of transport?

Answer 10

(1) Passive transport: movement of molecules down a concentration gradient
(2) Active transport: movement of molecules against their concentration gradient

Question 11

Examples of molecules that use passive transport

Answer 11

Weak acids and weak bases like aspirin, penicillin

Question 12

Examples of molecules that use active transport

Answer 12

Vitamin B12

Question 13

What do lipids do in membranes?

Answer 13

Provide fluidity to membranes.

Question 14

What do all lipids have in common?

Answer 14

They are all not soluble in water

Question 15

What constitutes phospholipids?

Answer 15

A glycerol with an ester link to two fatty acid chains and a phosphoryl polar head group

Question 16

What constitutes a fatty acid?

Answer 16

A carboxyl group which is hydrophilic and a long hydrocarbon chain which is hydrophobic

Question 17

Why are lipids special?

Answer 17

Their upper parts interact strongly with water (hydrophilic) whereas the lower part (the tail) stays away from water (hydrophobic)

Question 18

Which part of the lipid points away from water?

Answer 18

The hydrophobic fatty acid tails

Question 19

What does the fluidity and permeability of membranes depend on?

Answer 19

The saturation of the fatty acid tails

Question 20

How can you get a membrane to be more fluid permeable

Answer 20

Unsaturated fatty acids have double bonds in their hydrocarbons which causes kinks in the tail since there are no rotations around double bonds. As a result, the fatty acid tails cannot interact as easily together as if they were all straight (saturated) and the membrane becomes more fluid permeable.

Question 21

What does the enhances fluidity of a kinked phospholipid do?

Answer 21

Improve the function of the membrane at lower temperatures.

Question 22

What does the degree of saturation of fatty acids depend on?

Answer 22

(1) Temperatures

(2) Growth phases

Question 23

What should the membrane be like during the exponential phase (rapid growth)?

Answer 23

The membrane needs to be fluid so we have double bonds in the fatty acids.

Question 24

What happens during the stationary phase (no growth) ?

Answer 24

Cells will produce enzymes that will react with these double bonds and produce a propane cycle.