Membranes

Question 1

Lipids

Answer 1

Nonpolar
Hydrophobic
Insoluble in water

Question 2

Types of Lipids

Answer 2

Fatty acids
Triacylglycerides
Membrane lipids
Cholesterol

Question 3

Fatty Acids

Answer 3

Long-chain hydrocarbon carboxylic acids
-general formula=CH3(CH2)nCOO-
Amphipathic (COO- is polar)

Question 4

Saturated Fatty Acids

Answer 4

No double bonds

Question 5

Unsaturated Fatty Acids

Answer 5

Has double bonds

Question 6

Monounsaturated Fatty Acids

Answer 6

1 double bond

Question 7

Polyunsaturated Fatty Acids

Answer 7

More than 1 double bond

Question 8

Where are double bonds most common?

Answer 8

In cis conformation

Question 9

How do double bonds affect the melting point?

Answer 9

Decreasing the melting point by introducing kinks

Question 10

Shorthand Notation for Fatty Acids

Answer 10

(number of carbons):(number of double bonds)(delta)^where the bonds are

Question 11

How does length affect the melting point

Answer 11

Longer=higher melting point

Shorter=lower melting point

Question 12

How does saturation affect the melting point

Answer 12

Saturated=higher melting point
Unsaturated=lower melting point
Greater effect on melting point than length

Question 13

Triacylglycerol

Answer 13

Way of storing fatty acids

Very hydrophobic

Question 14

Triacylglycerol Structure

Answer 14

3 acyl chains attached to glycerol

Acyl chains from fatty acids (ester-linked)

Question 15

What type of triacylglycerols is most common?

Answer 15

Mixed TAGs

the melting point will be lower for those containing unsaturated fatty acids or shorter chains

Question 16

Glycerophospholipids

Answer 16

2 acyl groups and a large polar group attached to glycerol

amphipathic

Question 17

Cholesterol

Answer 17

Rigid, nonpolar structure
Weakly amphipathic
Found in membrane lipids
Does not form membranes alone
-associates with polar headgroups of other lipids
-nonpolar portion is found in the membrane

Question 18

Lipid Interactions in water

Answer 18

Fatty acids from micelles when mixed in water

Membrane lipids form a bilayer when mixed in water

Question 19

Dimensions of a lipid bilayer

Answer 19

Variable
Lipid head groups have significantly different dimensions
Acyl chains vary in length
Cholesterol is almost entirely buried in the bilayer

Question 20

The fluidity of membrane lipids

Answer 20

The melting temperature is the temperature of its transition from an ordered crystalline to a more fluid state
Depending on the acyl chain length and unsaturation

Question 21

Why is the transition temperature not sharp?

Answer 21

Mixture of compounds
Membranes must operate above melting point but not be completely disordered
Lipids must adjust to maintain fluidity

Question 22

How do membranes maintain fluidity?

Answer 22

Lower temperature = more unsaturated and shorter fatty acids are incorporated
Higher temperature = more saturated and longer fatty acids are incorporated

Question 23

How does cholesterol help maintain membrane fluidity?

Answer 23

Lower temperature = prevents packing between acyl chains

Higher temperature = decreases motion/disorder of acyl chains and increases rigidity

Question 24

Why do lipids only move laterally in the bilayer?

Answer 24

Provides membrane fluidity

-weakly hydrophobic interactions

Question 25

Why don't lipids undergo transverse diffusion?

Answer 25

The significant energy barrier for desolvating a polar head to move through the nonpolar bilayer -flipases would be needed

Question 26

Types of Membrane Proteins

Answer 26

``` Integral membrane protein -hydrophobic interactions Peripheral membrane protein -electrostatic/polar -easy to separate from lipid Lipid-linked protein -lipid prosthetic group -hydrophobic anchor ```

Question 27

Integral Membrane Proteins and Hydrophobic Amino Acids

Answer 27

The portion of protein connected to acyl tails must have hydrophobic amino acids side chains

Question 28

What can cross bilayer by diffusion

Answer 28

Small, nonpolar molecules

Question 29

What does the rate of diffusion depend on?

Answer 29

``` Size of molecule -smaller moves faster Concentration gradient -larger gradient increases the rate Lipid solubility -increases the diffusion rate ```

Question 30

Passive Transport

Answer 30

No ATP required | If G=negative, motion is spontaneous which is passive

Question 31

Active Transport

Answer 31

ATP required | If G=positive, energy is required which is active

Question 32

What does G need to be for transport to occur?

Answer 32

Negative

Question 33

Porins

Answer 33

Relatively non-specific Water-filled pore in the center of the barrel Most are trimers (3 pores) Passive

Question 34

Ion Channels

Answer 34

Highly selective Channel formed between subunits Selectivity depends on the size of the pore and the properties of the side chains/functional groups found there Can be passive or active

Question 35

Transporter Proteins

Answer 35

``` Carrier proteins No membrane-spanning pores Conformational change alternates openings Selective Passive or active ```

Question 36

Uniport

Answer 36

Transports one type of substrate

Question 37

Symport

Answer 37

Trasport of two molecules in the same direction

Question 38

Antiport

Answer 38

Transports two molecules in opposite directions | Secondary Active Transport

Question 39

Primary vs Secondary Active Transport

Answer 39

``` Primary = uses ATP as a source of free energy Secondary = uses ion gradient as a source of free energy ```