Question 1

Which of the following statements correctly describes an essential amino acid?

Accepted Answer

It must be obtained from the diet because the body cannot synthesize it.

Question 2

At physiological pH ($$pH \approx 7.4$$), what is the predominant form of the carboxyl group in an amino acid?

Accepted Answer

$$-COO^{-}$$

Question 3

Which amino acid is most likely to be found in the tight turns of a protein's beta-sheet due to its small size?

Accepted Answer

Glycine

Question 4

Given the following pKa values: amino group $$pK_a = 9.5$$, carboxyl group $$pK_a = 2.2$$, what is the net charge of a generic amino acid at $$pH = 1$$?

Accepted Answer

Net charge = +1

Question 5

Which of the following amino acids contains a sulfhydryl group and can form disulfide bonds?

Accepted Answer

Cysteine

Question 6

Which amino acid is a precursor for catecholamines such as dopamine and epinephrine?

Accepted Answer

Tyrosine

Question 7

At $$pH = 7.4$$, which of the following amino acids is positively charged?

Accepted Answer

Lysine

Question 8

Which amino acid is most likely to participate in hydrogen bonding due to its hydroxyl group?

Accepted Answer

Serine

Question 9

Which of the following best describes a zwitterion?

Accepted Answer

A molecule with both positive and negative charges but is overall neutral.

Question 10

Which amino acid is branched-chain and can be used as an energy source in muscle tissue?

Accepted Answer

Isoleucine

Question 11

In the Fischer projection, how do you distinguish an L-amino acid from a D-amino acid?

Accepted Answer

L-amino acid has the amino group on the left.

Question 12

Which amino acid is a precursor for serotonin and melatonin?

Accepted Answer

Tryptophan

Question 13

Which of the following amino acids is negatively charged at physiological pH?

Accepted Answer

Aspartate

Question 14

What is the expected charge of the amino group ($$pK_a = 9.5) at$$ $$pH = 7.4$$?

Accepted Answer

It is protonated and positively charged.

Question 15

Which amino acid is most likely to be used as fuel for intestinal cells and can be converted to glutamate after hydrolysis?

Accepted Answer

Glutamine

Question 16

Which of the following amino acids is aromatic and hydrophobic?

Accepted Answer

Phenylalanine

Question 17

Which amino acid contains a methyl group attached to sulfur and is hydrophobic?

Accepted Answer

Methionine

Question 18

Which of the following is true about the salt bridge in proteins?

Accepted Answer

It is an electrostatic interaction between oppositely charged side chains.

Question 19

Which amino acid is most likely to be neutral at physiological pH due to its side chain pKa being close to 7?

Accepted Answer

Histidine

Question 20

Which of the following amino acids is most likely to be involved in glycosylation due to its hydrolyzable amide group?

Accepted Answer

Asparagine

Amino Acid Structures and Properties – Study Notes for Biochemistry

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