Lecture 6 - Exam 1

Question 1

What is the more common secondary structure - alpha helix or beta sheets?

Answer 1

Alpha helix because it is the easiest thing to form. It can absorb mutations much better.

Question 2

What does allosteric mean?

Answer 2

Relating to or denoting the alteration of the activity of a protein through the binding of an effector molecule at a specific site.

Question 3

Most allosteric enzyme consist of _____ subunits.

Answer 3

Multiple

Question 4

Enzymes speed up the rate of a reaction, but they do not…?

Answer 4

They do not yield more product.

Question 5

What are the lipids of the outer cell membranes?

Answer 5

Phosphatidylcholine and Sphingomyelin (doesn’t contain glycerol)

Question 6

What are the lipids of the inner membrane and what are their charges?

Answer 6

Phosphatidylinositol : negatively charged
Phosphatidylserine : negatively charged (doesn’t have a glycerol or phosphate)
Phosphatidylethanolamine

Question 7

What are the other major components (biomacromolecules) of cell membranes?

Answer 7

Lipids ~ 45%
Proteins ~ 45%
Carbohydrates ~ 10%
Nucleic acids ~ 0%

Question 8

What are the cell membrane proteins?

Answer 8

1. Integral membrane (transmembrane) proteins: Inserted into the lipid bilayer. Can be released only by treatments that disrupt the phospholipid bilayer (detergents)
2. Peripheral proteins: Associated with the cell membrane through electrostatic interactions. Can be released by changing salt concentration or pH, no need to disrupt the cell membrane.
3. Lipid-anchored proteins: Covalently attached to phospholipids

Question 9

Integral membrane proteins have different _______

Answer 9

conformations:
alpha helix and beta barrels

Question 10

Peptide bonds are _____ bonded to each other in the interior of the helix while __________ interact with phospholipid chains.

Answer 10

hydrogen ; hydrophobic amino acid side chains

Question 11

The formation of the alpha-helix structure of the integral membrane proteins ____________ of the peptide bonds as well.

Answer 11

neutralizes the polar character

Question 12

Describe a beta barrel of an integral membrane protein.

Answer 12

The only other known protein to span lipid bilayers.
Polar side chain amino acids line the inside of the pore.
Non-polar side chain amino acids on the outside of the pore interact with the phospholipids.
Can be highly selective!!!
Mostly found on bacterial, mitochondrial or chloroplast outer membranes.

Question 13

Are transmembrane proteins amphipathic like phospholipids?

Answer 13

Yes

Question 14

What would happen if those cells were placed in a solution that contained a peptidase (an enzyme that degrades proteins)?

Answer 14

The peptidase would digest the loops on the outside of the cell and leave the beta barrel intact.
This is because proteins cannot enter the bilayer unless they are transmembrane proteins.