Chapter 12 (Exam 2)

Question 1

What are biological membranes?

Answer 1

Complex lipid-based structures that form pliable sheets and are composed of a variety of lipids and proteins.

Question 2

What is the purpose of a cell membrane?

Answer 2

Separates the cell from its surrounding.

Question 3

What do eukaryotic cells have?

Answer 3

Various internal membranes that divide the internal space into compartments (ex. organelles).

Question 4

What classes of lipids are found in membranes?

Answer 4

Phospholipids, glycolipids, steroids.

Question 5

Does maintaining the lipid bilayer require energy?

Answer 5

No because it happens spontaneously.

Question 6

What does the membrane bilayer consist of?

Answer 6

2 leaflets (layers) of lipid monolayers; the thickness of most membranes is 6 - 10 nm.

Question 7

When does the membrane bilayer form?

Answer 7

When lipids with polar head groups and more than one lipid tail are in aqueous solution.

Question 8

What do hydrophilic head groups interact with?

Answer 8

Water on both sides of the bilayer.

Question 9

How are hydrophobic fatty acid tails set up inside the membrane bilayer?

Answer 9

Packed inside.

Question 10

What is the structure of individual units in the membrane bilayer?

Answer 10

Cylindrical (cross section of head equals that of side chain).

Question 11

What is the nucleus surrounded by?

Answer 11

A double membrane, or 2 lipid bilayers, with occasional pores. Only one of the lipid bilayers is expanded.

Question 12

Are lipid bilayers highly impermeable to ions and most polar molecules?

Answer 12

Yes.

Question 13

What is the function of a molecule’s hydrophobicity?

Answer 13

The ability of small molecules to cross a membrane.

Question 14

Why is indole more soluble than tryptophan in membranes?

Answer 14

Because it is uncharged.

Question 15

Why can ions not cross membranes?

Answer 15

Because of the energy cost of shedding their associated water molecules.

Question 16

Can oxygen and CO2 pass the membrane?

Answer 16

Yes, because they are uncharged and small.

Question 17

Can steroid hormones pass through the membrane?

Answer 17

Yes, because they are pretty hydrophobic and nonpolar, so they can pass through the membrane easily without receptors.

Question 18

What is membrane fluidity determined by?

Answer 18

Mainly by the fatty acid composition.

Question 19

What do more fluid membranes require?

Answer 19

Shorter and more unsaturated fatty acids.
- Melting temperature decreases as double bonds are added.
- Melting temperature increases with length of saturated fatty acids.

Question 20

What do cells need at higher and lower temperatures?

Answer 20

Higher temperatures: cells need more long, saturated fatty acids.
Lower temperatures: cells need more unsaturated fatty acids.

Question 21

Can organisms adjust the membrane composition?

Answer 21

Yes.

Question 22

What is cholesterol?

Answer 22

The key modulator of membrane fluidity in animals.
Works as a buffer of membrane fluidity.
Amphipathic molecule.

Question 23

What does cholesterol disrupt?

Answer 23

The tight packing of fatty acid chains.

Question 24

What is the most abundant steroid in the body?

Answer 24

Cholesterol.

Question 25

What do proteins carry out?

Answer 25

Most membrane processes.

Question 26

How do lipids diffuse in memebranes.

Answer 26

Rapidly and laterally.
Very fast: 1 um/s.

Question 27

What is transverse diffusion (flip-flopping)?

Answer 27

Very rare without the assistance of enzymes.

Question 28

What can special enzymes catalyze?

Answer 28

Transverse diffusion.

Question 29

What does the prohibition of transverse diffusion account for?

Answer 29

The stability of membrane asymmetry.

Question 30

How long does transverse diffusion (flip-flopping) take?

Answer 30

Very slow.
t1/2 in days.

Question 31

What are the 2 types of passive transport?

Answer 31

Diffusion and Facilitated diffusion.

Question 32

What is passive diffusion?

Answer 32

Molecules go from high concentration to low concentration.
No energy involved.

Question 33

What are simple diffusion molecules?

Answer 33

CO2, O2, steroid hormones.

Question 34

What type of diffusion does glucose go through and why?

Answer 34

Facilitated diffusion.
Glucose needs a gate to go through the membrane from high to low concentration, still no energy needed as long as a door is present.
If there is a transporter for glucose, it goes through passive transport.

Question 35

What occurs in the sodium potassium pump?

Answer 35

Uses the energy of ATP hydrolysis to simultaneously pump 3 Na+ ions out of the cell and 2 K+ ions into the cell against their concentration gradient.

Question 36

What type of transport is the sodium potassium pump?

Answer 36

Active transport

Question 37

What do ABC transporters do?

Answer 37

Use ATP to pump different stuff against the gradient.

Question 38

What are the 2 parts of ABC transporters?

Answer 38

Membrane-spanning domain and ATP-binding cassette.

Question 39

How does chemotherapy relate to ABC transporters?

Answer 39

After a few months, the cancer cells become resistant to it.

Question 40

What do secondary transporters do?

Answer 40

Use one concentration gradient to power the formation of another.
Moves something from the membrane against the gradient, but that transporter doesn’t use ATP itself.

Question 41

What is a symporter?

Answer 41

Uses one molecule to move another against the gradient, but that transporter doesn’t use ATP itself.

Question 42

What is an antiporter?

Answer 42

Uses one molecule to move another against the gradient in the opposite direction.