Question 1

Which of the following statements best explains why polar amino acids are hydrophilic?

Accepted Answer

They have terminal electronegative atoms in their R groups, allowing them to form hydrogen bonds with water.

Question 2

Which amino acid among the following contains a thiol ($-\mathrm{SH}$) group in its side chain?

Accepted Answer

Cysteine

Question 3

A patient is found to have a mutation that replaces the hydroxyl group in threonine with a methyl group. What is the most likely effect on the protein's solubility?

Accepted Answer

Protein solubility will decrease because the side chain becomes less polar.

Question 4

Which of the following polar amino acids contains an amide functional group in its side chain?

Accepted Answer

Asparagine

Question 5

Given the following structure, identify the amino acid: $\mathrm{H_2N{-}CH(CH_2{-}SH){-}COOH}$

Accepted Answer

Cysteine

Question 6

Which of the following amino acids can participate in disulfide bond formation, stabilizing protein tertiary structure?

Accepted Answer

Cysteine

Question 7

A protein is found to have a high content of serine and threonine residues. Which property is most likely enhanced in this protein?

Accepted Answer

Hydrogen bonding with water

Question 8

Which of the following is the correct structure for the side chain of glutamine?

Accepted Answer

$-CH_2{-}CH_2{-}CONH_2$

Question 9

If a mutation changes asparagine to aspartic acid in a protein, what is the most likely effect on the protein's charge at physiological pH?

Accepted Answer

The protein will gain a negative charge.

Question 10

Which of the following amino acids is most likely to be found on the surface of a soluble protein in the cytoplasm?

Accepted Answer

Serine

Question 11

A researcher is studying a protein that forms hydrogen bonds with DNA. Which polar amino acid is most likely involved in this interaction?

Accepted Answer

Asparagine

Question 12

Which of the following best describes the difference between serine and threonine?

Accepted Answer

Threonine has an additional methyl group attached to the carbon bearing the hydroxyl group.

Question 13

Which of the following is the correct chemical formula for the side chain of serine?

Accepted Answer

$-CH_2{-}OH$

Question 14

A mutation in a protein replaces cysteine with serine. What is the most likely effect on the protein's ability to form covalent cross-links?

Accepted Answer

The protein will lose the ability to form disulfide bonds.

Question 15

Which of the following polar amino acids contains a hydroxyl group in its side chain?

Accepted Answer

Threonine

Question 16

Which amino acid is most likely to be involved in the active site of an enzyme that catalyzes phosphorylation reactions?

Accepted Answer

Serine

Question 17

A protein is mutated so that all threonine residues are replaced with valine. What is the most likely effect on the protein's interaction with water?

Accepted Answer

The protein will become less hydrophilic due to loss of polar side chains.

Question 18

Which of the following amino acids is classified as polar but uncharged at physiological pH?

Accepted Answer

Asparagine

Question 19

Which of the following is a common property shared by all the polar amino acids listed (Ser, Thr, Cys, Asn, Gln)?

Accepted Answer

They all have side chains capable of forming hydrogen bonds.

Polar Amino Acids: Structure and Properties

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