Amino Acids, Peptides, and Proteins

Question 1

What are the groups attached to an amino acid?

Answer 1

amino group, carboxylic acid, hydrogen atom, and an R group attached to a central alpha carbon

Question 2

Amino acids are chiral (L) except for ______.

Answer 2

Glycine

Question 3

What configuration do amino acids have? (R or S)? Exceptions?

Answer 3

S except for Cysteine

Question 4

Nonpolar, nonaromatic amino acids?

Answer 4

glycine, alanine, valine, leucine, isoleucine, methionine, proline

Question 5

Aromatic amino acids?

Answer 5

tryptophan, phenylalanine, tyrosine

Question 6

Polar amino acids?

Answer 6

serine, threonine, asparagnine, glutamine, cysteine

Question 7

Negatively charged (acidic) amino acids?

Answer 7

aspartic acid, glutamic acid

Question 8

Positively charged (basic) amino acids?

Answer 8

lysine, arginine, histidine

Question 9

T/F

Amino acids are amphoteric.

Answer 9

True

Question 10

At low pH (acidic), amino acids are ______.

Answer 10

protonated

Question 11

At neutral pH, amino acids are ______.

Answer 11

zwitterions

Question 12

At high pH (basic), amino acids are ______.

Answer 12

deprotonated

Question 13

How is pI determined?

Answer 13

averaging the pKa values that refer to protonation and deprotonation of the zwitterion

Question 14

How are peptide bonds formed?

Answer 14

through a condensation (dehydration) reaction with a nucleophilic amino group attacking an electrophilic carbonyl

Question 15

How are peptides bonds broken?

Answer 15

hydrolysis

Question 16

Primary structure?

Answer 16

linear sequence of amino acids

Question 17

Secondary structure?

Answer 17

local structure, stabilized by H bonding

• alpha helices
• beta pleated sheets

Question 18

Tertiary structure?

Answer 18

3-D structure stabilized by hydrophobic interactions, acid-base interactions (salt bridges), H bonding, and disulfide bonds
-1 polypeptide

Question 19

Quaternary structure?

Answer 19

interactions between subunits

-multiple polypeptides

Question 20

Heat and solutes can cause _____.

Answer 20

denaturation