Lipids and membrane structure

Question 1

How are phospholipid molecules orient themselves in a bilayer

Answer 1

Fatty acid tails face inwards, away from aqueous exterior of membrane

Question 2

What type of membrane is the only one on which carbohydrates are found?

Answer 2

Plasma membrane

Question 3

How are lipids used?

Answer 3

Energy storage (triacylglycerides)
Precursors fro vitamins and steroid hormones (such as testosterone and oestrogen)
Production of bile acids such as cholic acid.

Question 4

What is the structure of a phospholipid?

Answer 4

Polar head group = phosphate = serine/choline/ethanolamine/inositol attached to glycerol by the phosphate group.
Then two fatty acid chains are linked to the glycerol back bone by ester bonds.

Question 5

Amphipathic

Answer 5

Has a polar side and a non-polar side

Question 6

What is the structure of phophatidylcholine?

Answer 6

choline - phosphate - glycerol = (fatty acid chain)2

Question 7

What phospholipid lacks a glycerol backbone?

Answer 7

Sphingomyelin

Question 8

What is the structure of sphingomyelin?

Answer 8

Ceramide (sphingosine + fatty acid) - phosphate - choline

Question 9

What are the pairs of lipids that make up each side of a phospholipid bilayer?

Answer 9

Phosphatidylcholine and sphingomyelin face the extracellular environment; phosphatidylserine and phosphatidylethanolamine face the cytosolic side

Question 10

Where are glycosylated proteins found in a membrane

Answer 10

Only on the extracellular face of the membrane

Question 11

What is fluidity in terms of a membrane and why is it important?

Answer 11

The ease with which lipid molecules can move about in the plane of the bilayer. Important for:
Movement of proteins; signalling and exocytosis.

Question 12

How can fatty acids affect the fluidity of a membrane?

Answer 12

The length of the chain: longer the chain the carbon atoms there are and so the greater the VDW forces and therefore a greater degree of stability - less fluidity.
The saturation of the fatty acid chain: saturation causes kinks in the acyl chain meaning there is a reduced molecule-to-molecule SA - less VDW forces, less stability and therefore more fluidity.

Question 13

How does the presence of cholesterol affect the fluidity of a membrane

Answer 13

Cholesterol restricts the movement of polar head groups, making things more ordered and so increasing stability; decreasing fluidity..

Question 14

What functions can proteins serve within a membrane.

Answer 14

I = ion channels
R = receptors
E = enzymes
S = structural 
T = transport

Question 15

Give the function of, and an example of an ion channel in the membrane:

Answer 15

Maintenance of ionic gradient; acetylcholine

Question 16

Give the function of, and an example of a receptor in the membrane:

Answer 16

Signal recognition; insulin receptor

Question 17

Give the function of, and an example of an enzyme in the membrane:

Answer 17

Catalysis; adenylyl cyclase

Question 18

Give the function of, and an example of a structural protein in the membrane:

Answer 18

Cell-to-cell contact + cytoskeletal organisation;

actin

Question 19

Give the function of, and an example of a transport protein in the membrane:

Answer 19

Import/export of substances;

glucose transporter

Question 20

What are the types of membrane protein?

Answer 20

Intrinsic = embedded in lipid bilayer
Anchored = covalently bonded to lipi molecule or to a sugar-arm of a glycolipid
Extrinsic = attached by ionic interactions with integral proteins for example spectrin (structural)