Biological Membranes

Question 1

Name the four lipid classes

Answer 1

F.a., triacylglycerols, membrane lipids, cholesterol

Question 2

Most naturally occurring double bonds are in what conformation?

Answer 2

cis

Question 3

Most common length of f.a.?

Answer 3

16 or 18

Question 4

Fatty acids are amphipathic, meaning?

Answer 4

Polar and nonpolar portions

Question 5

What is the problem with unsaturated f.a.?

Answer 5

Cannot pack together effectively. When packed together, VDW interactions are maximized

Question 6

What affects f.a. melting point?

Answer 6

Length and unsaturation

Question 7

Longer fatty acids lead to _____ melting point

Answer 7

higher

Question 8

Unsaturated f.a. melt at _______ temperatures

Answer 8

lower (less VDW interactions bc kinks)

Question 9

Which double bonds alter f.a. shape?

Answer 9

cis

Question 10

How are f.a. stored?

Answer 10

As fat (triacylglycerols or TAGS)

Question 11

What are the three classes of membrane lipid?

Answer 11

Glycerophospholipids, Sphingolipids, cholesterol

Question 12

Characteristics of cholesterol

Answer 12

Weakly amphipathic (sterol), not found in bacteria. Mostly hydrophobic, membrane lipid in mammalian plasma membranes

Question 13

What does cholesterol do

Answer 13

Maintains fluidity and rigidity

Question 14

When in water, what happens to amphipathic molecules

Answer 14

They form a micelle (when wedge-shaped) or bilayer (when cylindrical)
Bilayer can assemble into closed vesicle (liposome)

Question 15

Can cholesterol form membranes alone?

Answer 15

No, OH associates with polar headgroups while non-polar portion is found in the membrane

Question 16

Bilayers vary depending on…

Answer 16

Lipid composition (f.a. chain and polar head)

Question 17

How does lipid composition vary

Answer 17

Size of head group, acyl tails vary in length (16-20 atoms), amount of cholesterol varies

Question 18

Lipid bilayers are _____ yet _____

Answer 18

fluid, stable

Question 19

What happens at a lipid bilayers melting temperature

Answer 19

Lipid molecules and chains move freely and rapidly. Ordered gel phase to fluid crystalline phase

Question 20

What affects membrane fluidity

Answer 20

Temperature, lipid composition (presence of cholesterol, f.a. chain length, degree of saturation)

Question 21

What is a bilayers transition temperature

Answer 21

The melting temperature

Question 22

How does cholesterol regulate membrane fluidity at high and low temperatures

Answer 22

High = rigid and planar, limits rotational movement of acyl tails, increasing VDW interactions
Low = inserts btw phospholipids and prevents them from clustering together and stiffening

Question 23

If temperatures decrease, how would you maintain membrane fluidity

Answer 23

More unsaturated f.a. and shorter chain length

Question 24

How can lipids move in a bilayer

Answer 24

Move freely and rapidly laterally, no flip-flop movement (significant energy barrier to moving polar head group through bilayer)

Question 25

What are the three types of membrane proteins

Answer 25

Integral, peripheral, lipid-linked

Question 26

What is the portion of an integral membrane (transmembrane) protein that is in contact with the acyl tails

Answer 26

Hydrophobic a.a. sidechains

Question 27

What are the two forms of transmembrane protein

Answer 27

a-helices and B-barrels (antiparallel)

Question 28

How can you tell how many times a protein has passed through the membrane

Answer 28

The number of different secondary structures

Question 29

How do small molecules cross the lipid bilayer

Answer 29

Simple diffusion

Question 30

What are the two major types of transport across biological membranes

Answer 30

Active and passive

Question 31

What kind of transport are porins and ion channels

Answer 31

Passive

Question 32

What are the differences between porins and ion channels

Answer 32

Porins = trimers (3 subunits; each contains a pore), non-selective
Ion channels = form between subunits, highly selective

Question 33

What are transportER proteins

Answer 33

Do not have pores, selective for substrate, requires energy