MMT: Amino Acids and Proteins

Question 1

name some of the major functions of proteins

Answer 1

1. transporters of hydrophobic compounds
2. cell adhesion molecules attach cells to each other and to extracellular matrix
3. hormones carry signals from one group of cells to another
4. ion channels through lipid membranes
5. enzymes that increase the rate of biochemical reactions

Question 2

define the relationship between pKa, pH, and protonation

Answer 2

if pH is lower than pKa, molecules are protonated.

if pH is higher than pKa, molecules are deprotonated

if pH = pKa, about 50% of molecules are protonated

Question 3

how is a peptide bond formed?

Answer 3

via a dehydration synthesis/condensation reaction

Question 4

describe hydropathy index

Answer 4

a measurement of the hydrophobicity of an amino acid side chain. higher index = more hydrophobic

Question 5

what is the most hydrophobic amino acid? the least?

Answer 5

most: isoleucine

least: arginine

Question 6

of the two sulfur containing amino acids, which can form disulfide bridges? what is this important for?

Answer 6

cysteine; the folding of proteins

Question 7

true or false: a disulfide bond is a reversible bond

Answer 7

true

Question 8

there are two amino acids commonly found at protein binding sites. what are they and why is this?

Answer 8

lysine and arginine; their side chains can form ionic bonds with negatively charged compounds such as ATP

Question 9

what is a post-translational modification? what is their purpose? when do they occur in the folding priocess?

Answer 9

the modification of a protein after synthesis has been completed; they can impact the function of the protein. they tend to occur after a protein is folded into its 3 dimensional conformation

Question 10

O-glycosylation: what it is, which amino acid(s) it happens to, type of proteins they’re found in

Answer 10

1. the addition of a carbohydrate to an OH group
2. serine, threonine, tyrosine
3. secreted proteins

Question 11

N-glycosylation: what it is, which amino acid(s) it happens to, what proteins it tends to be found in

Answer 11

1. the addition of a carbohydrate to NH2
2. asparagine
3. cell surface proteins

Question 12

what is palmitoylation?

Answer 12

addition of lipid to internal SH in cysteine; major form of fatty acylation in the body!

Question 13

what is prenylation?

Answer 13

addition of lipid to SH group

Question 14

what type of glycosylation protects against proteolysis?

Answer 14

N

Question 15

what is myristoylation

Answer 15

addition of lipid to N-terminal of glycine

Question 16

name major types of regulatory modifications and what amino acids they apply to

Answer 16

acetylation (lysine), phosphorylation (serine, threonine, tyrosine), ADP ribosylation (arginine, glutamine, cysteine

Question 17

what enzyme is involved in phosphorylation

Answer 17

protein kinases

Question 18

what is the most commonly hydroxylated amino acid?

Answer 18

proline

Question 19

describe carboxylation as it is relevant to the clotting process

Answer 19

carboxylation of the 4th carbon in glutamate is important for attaching the clot to a surface