Lecture 10: Structure of Biological Membranes

Question 1

What is the function of a carbohydrate and the different types?

Answer 1

• They are located on the outer surface of the membrane
• Serve as recognition sites for other molecules
• EX:
• Glycolipid: a carb covalently bounded to a lipid (recognition signal between cells)
• Glycoprotein: one or more short carb chains covalenty bound to a protein (cell recognition and adhesion)
• Proteoglycans: numerous long polysaccharides (cell recognition and adhesion)

Question 2

Why are cholesterol important to have in a membrane?

Answer 2

• Cholesterol is crucial to influence the fluidity of the membrane.
• More cholesterol = less fluidity
• Less cholesterol = more fluidity

Question 3

Saturated FA vs Unsaturated FA in the membrane

Answer 3

• Long saturated FA allow for tighter packing
• Unsaturated FA make membrane less dense, more fluid

(the longer they are the more interactions, less permeability)

Question 4

What are the 2 different kinds of membrane proteins?

Answer 4

Integral Membrane Proteins: at least partially embedded in the membrane, contain hydrophobic and hydrophillic regions (Sodium Channel)

Peripheral Membrane Protein: lack surface hydrophobic groups, have polar or charged regions that alowd them to interact with exposed membrane proteins or pola r heads of phsopholipids (Phospholipase C)

Question 5

What are CAMs and some examples?

Answer 5

CAMs are cell adhesion molecules and they are involved in binding with other cells or the extracellular matrix. There are transmembrane proteins with 3 regions: extracelular, transmembrane, and intracellular domain (interacts with cytoskeleton)

Major groups of CAMs :
- Immunoglobulins
- Integrins
- Cadherins
- Selectins

Question 6

What are integrins and what do they do?

Answer 6

• They allow for attachment of cells to extracellular matrix and cell to cell interaction
• They also allow for cell movement during embryogensis and during metasasis (spread of cancer)

Question 7

What are the different forms of cell junctions for animal cells?

Answer 7

• Tight Junctions : form a tight quilted seal
• Desmosomal adhesion : link adjacent cells tightly but permit materals to move around them
• Gap junctions: let adjacent cells communicate utilizing protein channels (connexins)