$$\text{pH} = \text{p}K_a + \log \left( \frac{[A^-]}{[HA]} \right)$$

Question 1

Which structural feature distinguishes all proteinogenic amino acids from other naturally occurring amino acids?

Accepted Answer

Presence of both an amino group and a carboxyl group attached to the alpha carbon

Question 2

Which amino acid is classified as nonpolar due to its alkyl side chain?

Accepted Answer

Valine

Question 3

What is the significance of the isoelectric point (pI) for an amino acid?

Accepted Answer

It is the pH at which the amino acid has no net electric charge

Question 4

Which equation is used to calculate the pH of a solution containing a weak acid and its conjugate base?

Accepted Answer

$$	ext{pH} = 	ext{p}K_a + \log \left( \frac{[A^-]}{[HA]} ight)$$

Question 5

Which amino acid is essential in the diet of humans because it cannot be synthesized in the body?

Accepted Answer

Leucine

Question 6

A patient with Maple Syrup Urine Disease is unable to properly metabolize which group of amino acids?

Accepted Answer

Branched-chain amino acids

Question 7

Which amino acid is classified as acidic due to the presence of a second carboxyl group in its side chain?

Accepted Answer

Aspartic acid

Question 8

What is the charge of glycine at its isoelectric point?

Accepted Answer

0

Question 9

Which amino acid is both glucogenic and ketogenic?

Accepted Answer

Tyrosine

Question 10

During electrophoresis at a pH below the isoelectric point, which direction will an amino acid migrate?

Accepted Answer

Toward the negative electrode (cathode)

Question 11

Which post-translational modification is most commonly found on histones and can regulate gene expression?

Accepted Answer

Methylation

Question 12

What is the main function of glutathione in erythrocytes?

Accepted Answer

Maintaining hemoglobin in the reduced (Fe$$^{2+}) $$state

Question 13

Which amino acid is a precursor for serotonin and melatonin?

Accepted Answer

Tryptophan

Question 14

Which amino acid is classified as a heterocyclic amino acid?

Accepted Answer

Proline

Question 15

Which amino acid is incorporated into proteins at a UGA codon, which is normally a stop codon?

Accepted Answer

Selenocysteine

Question 16

What is the main catalytic feature of pyridoxal phosphate (PLP) in enzyme-catalyzed reactions?

Accepted Answer

Its electro-philic nitrogen acting as an electron sink

Question 17

Which amino acid is conditionally essential, required in the diet only if phenylalanine is deficient?

Accepted Answer

Tyrosine

Question 18

Which property of the peptide bond restricts rotation around the C-N bond?

Accepted Answer

Partial double bond character

Question 19

Which amino acid is a component of pantothenic acid, an essential nutrient in the vitamin B complex?

Accepted Answer

Beta-alanine

Question 20

Which amino acid is most likely to form disulfide bonds, contributing to protein structure stability?

Accepted Answer

Cysteine

Amino Acids: Structure, Classification, and Chemical Properties

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