Question 1

Which of the following statements best describes the primary structure of a protein?

Accepted Answer

It is the linear sequence of amino acids linked by peptide bonds.

Question 2

Which amino acid is classified as non-essential and has the simplest side chain?

Accepted Answer

Glycine

Question 3

What is the main function of the carboxyl group in amino acids at physiological pH?

Accepted Answer

It acts as a proton acceptor, becoming negatively charged ($$COO^-).$$

Question 4

Which amino acid contains a side chain with a hydroxyl group and is a common site for phosphorylation?

Accepted Answer

Serine

Question 5

At a pH below the isoelectric point (pHi) of an amino acid, what is the net charge of the molecule?

Accepted Answer

Positive

Question 6

Which amino acid is most likely to be found in the interior of water-soluble proteins due to its hydrophobic nature?

Accepted Answer

Leucine

Question 7

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

Accepted Answer

$$pH = pK_a + \log \frac{[A^-]}{[HA]}$$

Question 8

Which amino acid is unique in that it does not have a chiral alpha carbon?

Accepted Answer

Glycine

Question 9

What is the role of methionine in protein synthesis?

Accepted Answer

It is the first amino acid incorporated at the N-terminus during translation.

Question 10

Which amino acid is most basic and always positively charged at physiological pH?

Accepted Answer

Arginine

Question 11

During electrophoresis at pH 6.3, which amino acid will migrate toward the anode?

Accepted Answer

Aspartic acid (pHi = 3)

Question 12

Which amino acid is a precursor for the neurotransmitter serotonin?

Accepted Answer

Tryptophan

Question 13

Which property increases the solubility of an amino acid in water?

Accepted Answer

Presence of a polar or ionizable side chain

Question 14

Which amino acid can form disulfide bonds, contributing to protein stability?

Accepted Answer

Cysteine

Question 15

What is the isoelectric point (pHi) of an amino acid?

Accepted Answer

The pH at which the net charge of the amino acid is zero

Question 16

Which amino acid is classified as essential and has an imidazole side chain?

Accepted Answer

Histidine

Question 17

Which amino acid is most abundant in blood and has a non-protonable amide side chain?

Accepted Answer

Glutamine

Question 18

Which amino acid is classified as aromatic and absorbs UV light at around 280 nm?

Accepted Answer

Tryptophan

Question 19

Which amino acid is classified as semi-essential due to its consumption in the ornithine cycle?

Accepted Answer

Arginine

Question 20

Which of the following amino acids is NOT classified as essential for humans?

Accepted Answer

Glycine

Amino Acids and Proteins: Structure, Properties, and Classification

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