Question 1

Which of the following statements best describes the zwitterionic form of an amino acid at physiological pH?

Accepted Answer

The amino group is protonated and the carboxyl group is deprotonated, resulting in both positive and negative charges with a net zero charge.

Question 2

Which amino acid is NOT chiral and why?

Accepted Answer

Glycine, because its side chain is a hydrogen atom.

Question 3

A protein sample absorbs strongly at 280 nm. Which amino acids are most likely responsible for this absorbance?

Accepted Answer

Phenylalanine, Tyrosine, and Tryptophan

Question 4

Which of the following amino acids contains a sulfur atom in its side chain and is classified as hydrophobic?

Accepted Answer

Methionine

Question 5

Given the following pKa values for glycine: $$pK_a$$^{COOH}$$ = 2.4$$, $$pK_a$$^{NH_3^+}$$ = 9.8$$, calculate the isoelectric point ($$pI) of $$glycine.

Accepted Answer

$$pI = \frac{2.4 + 9.8}{2} = 6.1$$

Question 6

Which amino acid is most likely to form a disulfide bond in proteins, and under what cellular conditions does this typically occur?

Accepted Answer

Cysteine, in the oxidizing environment of the endoplasmic reticulum

Question 7

Which of the following amino acids is classified as basic and has a side chain pKa closest to physiological pH?

Accepted Answer

Histidine

Question 8

A mutation replaces a glutamate (Glu, E) residue with lysine (Lys, K) in a protein. What is the most significant chemical change at this position?

Accepted Answer

A negatively charged side chain is replaced with a positively charged side chain.

Question 9

Which mnemonic is commonly used to identify the L-enantiomer of amino acids when viewing the Fischer projection?

Accepted Answer

CORN, when reading from the hydrogen towards the alpha carbon

Question 10

Which amino acid is most likely to act as a nucleophile at physiological pH due to its imidazole side chain?

Accepted Answer

Histidine

Question 11

Which property is shared by all biological macromolecules, including proteins, nucleic acids, carbohydrates, and lipids?

Accepted Answer

They are composed of monomeric units and have 3-dimensional structures.

Question 12

Which amino acid is most likely to be found in the interior of a globular protein due to its hydrophobic nature?

Accepted Answer

Leucine

Question 13

Which of the following modifications increases the number of side chain functional groups in proteins post-translationally?

Accepted Answer

Phosphorylation of serine

Question 14

Which amino acid is most likely to bind reactive metals due to its negatively charged carboxylate side chain at neutral pH?

Accepted Answer

Aspartate

Question 15

Which amino acid is most likely to disrupt alpha-helical structure due to its cyclic side chain?

Accepted Answer

Proline

Question 16

Which of the following amino acids is classified as aromatic and can participate in hydrogen bonding due to its hydroxyl group?

Accepted Answer

Tyrosine

Question 17

Which equation describes the Beer-Lambert law used to quantify protein concentration using absorbance at 280 nm?

Accepted Answer

$$A = \varepsilon c l$$

Question 18

Which amino acid is most likely to be involved in hydrogen bonding due to its amide side chain?

Accepted Answer

Glutamine

Question 19

Which of the following best explains why modifications of amino acids are important in proteins?

Accepted Answer

They increase the diversity of protein function by adding new chemical groups.

Question 20

Which amino acid is most likely to act as a nucleophile when its hydroxyl group is deprotonated?

Accepted Answer

Serine

Structure and Properties of Amino Acids

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