Biological Membranes

Question 1

Lipid rafts

Answer 1

large grouping of lipids held together by cholesterol
have a relatively high conc. of sphingomyelins
can diffuse within the bilayer, help with stability, important in regulating signaling process

Question 2

Cholesterol

Answer 2

helps regulate fluidity of membrane under a variety of temps
high temp = decrease membrane fluidity, so you need to get rid of them to regulate
low temp = increase fluidity, so you need to have more of them to regulate

Question 3

Fatty acids for regulating fluidity

Answer 3

saturated = decrease fluidity
unsaturated = promote fluidity

Question 4

Three classes of lipids

Answer 4

phospholipids
sterols (cholesterol)
glycolipids

Question 5

Phospholipids

Answer 5

can move freely in the horizontal direction across bilayer
flipping from the intracellular cell to extracellular (or vise versa) requires flippases and is energetically costly
predominant component of the bilayers

Question 6

Glycolipids

Answer 6

involved in communication because they have a carbohydrate moiety attached to the head - allows for signaling properties
also involved in structure - same large-scale structure as a phospholipid except you have either glycerol or sphingosine backbone

Question 7

Main classes of membrane proteins

Answer 7

Transmembrane (integral)
Peripheral
Lipid anchored

Question 8

Transmembrane (integral) proteins

Answer 8

examples: proton pumps, ion channels, G protein-coupled receptors
have a hydrophilic, cytosolic domain that interacts with the intracellular environment
hydrophilic domain that interacts with the extracellular environment
hydrophobili/lipiophilic domain that interacts with the hydrophobic membrane and anchors the protein

Question 9

Peripheral

Answer 9

transiently interact with the lipid bilayer, but tend to have some other major function
example: hormones, enzymes
they are transiently attached to an integral protein or are bound to the phospholipids at the periphery

Question 10

Lipid-anchored

Answer 10

covalently bound to a single or multiple lipids
don’t have a domain that sticks out to the extracellular/intracellular invironments
example: G protein

Question 11

Common types of glycosylation of proteins

Answer 11

O-glycosylation - the O group on serine and threonine is glycosylated (oligosaccharide chain added)
N-glycosylation - the N side chain on asparagine is glycosylated

Question 12

What can pass through membrane without a channel?

Answer 12

small non-polar molecules