Biochemistry Chapter 1: Amino Acids, Peptides and Proteins

Question 1

What are the 4 groups attached to the alpha-carbon?

Answer 1

R group, carboxylic acid group, amino group & a hydrogen

Question 2

What is the stereochemistry for all amino acids in eukaryotes?

Answer 2

L

Question 3

Where are D amino acids found?

Answer 3

They can exist in prokaryotes

Question 4

Which amino acid does not have an S configuration?

Answer 4

cysteine

Question 5

All amino acids are chiral except…

Answer 5

glycine (H)

Question 6

What are the nonpolar, nonaromatic amino acids?

Answer 6

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

Question 7

What are the aromatic amino acids?

Answer 7

tryptophan, phenylalanine, tyrosine

Question 8

What are the polar amino acids?

Answer 8

serine, threonine, asparagine, glutamine, cysteine

Question 9

What are the acidic amino acids?

Answer 9

aspartate, glutamate

Question 10

What are the basic amino acids?

Answer 10

lysine, arginine, histidine

Question 11

What does amphoteric mean?

Answer 11

They can accept or donate protons

Question 12

what is the pka?

Answer 12

the pH at which half of the species is deprotonated; (HA) = (A-)

Question 13

At low pH, the amino acid is…

Answer 13

Fully protonated

Question 14

At pH near pI, the amino acid is…

Answer 14

a neutral zwitterion

Question 15

at high pH, the amino acid is…

Answer 15

fully deprotonated

Question 16

How can the isoelectric point, pI, be calculated?

Answer 16

calculating the average of the two pKa values

Question 17

How can you tell the pKa from a titration curve? pI?

Answer 17

flat at pka values & nearly vertical at the pI

Question 18

Amino acids without charged side chains have a pI around…

Answer 18

6

Question 19

Acidic amino acids have a pI…

Answer 19

Well below 6

Question 20

Basic amino acids have a pI…

Answer 20

Well above 6

Question 21

How is a peptide bond formed?

Answer 21

condensation or dehydration; the nucleophilic amino group of one amino acid attacks the electrophilic carbonyl group of another amino acid

Question 22

Why are amide bonds rigid?

Answer 22

resonance

Question 23

How do you break a peptide bond?

Answer 23

hydrolysis

Question 24

What amino acid can interrupt secondary structure of a protein?

Answer 24

Proline because of its rigid cyclic structure

Question 25

What can lead to protein denaturation?

Answer 25

heat and increasing solute concentration