Lipids and membrane structure

Question 1

Features of phospholipids

Answer 1

-Major component of all membranes
-Spontaneously form bilayer in aqueous environments
-Polar head group attached to backbone (glycerol) by phosphate group
-2 fatty acyl side chains lined to glycerol backbone via ester bonds
-Amphipathic - polar head group and non-polar FA tail

Question 2

What is the fluid mosiac model of membrane structure?

Answer 2

-Islands of protein in a sea of lipid
-Hydrophilic heads -Hydrophobic tails
-4-5nm width

Question 3

How does the composition of cell membranes vary?

Answer 3

-Only plasma membrane has glycosylated proteins
-Lipid bilayers are asymmetrical

Question 4

What is membrane fluidity and why is it important?

Answer 4

-the ease with which lipid molecules move about in the plane of the bilayer
-important in the regulation of membrane function (movement of proteins, signalling, exocytosis)

Question 5

What are the 4 layers of cell membrane and major component of each one?

Answer 5

-Plasma membrane
=>cholesterol
-Outer mitochondrial membrane
-Inner mitochondrial membrane
-Nuclear membrane
=>phosphatidylcholine

Question 6

What regulates membrane fluidity?

Answer 6

-Increase in short chain fatty acids reduces van der waals interactions between fatty acids which increases fluidity
-Kinks in unsaturated fatty acids reduce van der waals interactions with other lipids and increases fluidity
-High cholesterol content restricts random movement of polar heads, orders the lipid bilayer and decreases fluidity

Question 7

What are lipid rafts?

Answer 7

-Specialised membrane microdomain
-More ordered, less fluid
-Increased level of cholesterol
-Increased level of sphingomyelin and gangliosides
-Allows close interaction between receptors and signalling molecules

Question 8

What are the types of membrane proteins?

Answer 8

-Structural
-Receptors
-Ion channels
-Transporters
-Enzymes

Question 9

What are integral (intrinsic) proteins?

Answer 9

-Embedded in lipid bilayer
-Most span entire bilayer
-Transmembrane spanning domains are alpha helices or beta sheets

Question 10

What are anchored proteins?

Answer 10

-Anchored to membrane by covalent bonds with fatty acids

Question 11

What are peripheral (extrinsic) proteins?

Answer 11

-Attach to membrane surface by ionic interactions with integral proteins or with polar head group of phospholipids