Organic Chemistry: Amino Acids, Peptides, and Proteins

Question 1

What type of enantiomers are naturally occurring amino acids?

Answer 1

All are L-enantiomers, except for glycine, which is achiral. The amino group would be on the left of a Fischer Projection.

Question 2

How do amino acids exist at neutral pH?

Answer 2

At neutral pH, amino acids are zwitterions, with a negative carboxyl group and a positive amino group. Furthermore, amino acids are amphoteric with at least two dissociation constants.

Question 3

When pH < pI, what is the charge of an amino acid?

Answer 3

Positive

Question 4

When pH > pI, what is the charge of an amino acid?

Answer 4

Negative

Question 5

Where does the pI lie?

Answer 5

Between pK1 and pK2

Question 6

What happens to amino acids when titrated with a base?

Answer 6

The carboxyl group deprotonates before the amino group.There are two buffering stages.

Question 7

What are the nonpolar amino acids?

Answer 7

Hydrophobic R groups that decrease solubility in water: Proline, Phenylalanine, Glycine, Tryptophan, Alanine, Methionine, Valine, Leucine, and Isoleucine

Question 8

Which are the polar amino acids?

Answer 8

Polar, uncharged, hydrophilic R-groups: Tyrosine, Asparagine, Glutamine, Serine, Threonine, and Cysteine

Question 9

What are the acidic amino acids?

Answer 9

R-group has a carboxyl group with a net negative charge at physiological pH, pI shifted towards acidic pH, and three pKa’s: Aspartic Acid, Glutamic Acid

Question 10

What are the basic amino acids?

Answer 10

R-group has an amino group with a positive charge at physiological pH, pI shifted towards basic pH, and three pKa’s: Arginine, Lysine, and Histidine

Question 11

What bonds join amino acids together?

Answer 11

Peptide bonds between on carboxyl group and the amino group of another via a condensation reaction.