Question 1

Which of the following statements best describes a zwitterion form of an α-amino acid at neutral pH?

Accepted Answer

The amino group is protonated and the carboxyl group is deprotonated.

Question 2

Which amino acid does NOT have a chiral α-carbon?

Accepted Answer

Glycine

Question 3

Amino acids can act as both acids and bases. What is the term for such molecules?

Accepted Answer

Ampholytes

Question 4

Which of the following best explains why proteins absorb strongly at 280 nm in UV spectroscopy?

Accepted Answer

Due to the aromatic side chains of tyrosine and tryptophan.

Question 5

Which of the following modifications is most likely to regulate protein function by adding a phosphate group to an amino acid residue?

Accepted Answer

Phosphorylation

Question 6

What is the main driving force for peptide bond formation between two amino acids?

Accepted Answer

It is coupled to ATP hydrolysis during protein synthesis.

Question 7

Which of the following best describes the relationship between L-alanine and D-alanine?

Accepted Answer

They are enantiomers.

Question 8

A peptide bond is formed by the condensation of which two functional groups?

Accepted Answer

Amino group and carboxyl group

Question 9

Which of the following statements about peptide bond hydrolysis is correct?

Accepted Answer

Peptide bonds are stable unless exposed to strong acid at high temperature or specific enzymes.

Question 10

If a tetrapeptide has the sequence Lys-Glu-Ala-Gly, what is the net charge of the peptide at pH 7? (Assume the N-terminus and C-terminus are free and use the following pKa values: Lys side chain = 10.5, Glu side chain = 4.2, N-term = 9.0, C-term = 2.0)

Accepted Answer

$+1$

Question 11

Which of the following best describes the effect of a nearby positive charge on the pK$_a$ of a glutamic acid side chain?

Accepted Answer

The pK$_a$ is decreased.

Question 12

Which of the following is a common post-translational modification that can affect protein structure and function?

Accepted Answer

Phosphorylation of serine residues

Question 13

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

Accepted Answer

Leucine

Question 14

Which of the following best explains why glycine is unique among the 20 common amino acids?

Accepted Answer

Its side chain is a hydrogen atom, making it achiral.

Question 15

A researcher is analyzing a protein sample using UV absorbance at 280 nm. Which amino acid residues are most responsible for the absorbance at this wavelength?

Accepted Answer

Tyrosine and tryptophan

Question 16

Which of the following statements about peptide bond formation is correct?

Accepted Answer

It is a condensation reaction that releases water.

Question 17

Which of the following best describes the term 'enantiomers' as it applies to amino acids?

Accepted Answer

Molecules that are mirror images and non-superimposable

Question 18

Which of the following is true regarding the ionization of a peptide as pH increases?

Accepted Answer

The overall charge becomes more negative.

Question 19

Which of the following best describes the effect of the environment on the pK$_a$ of an amino acid side chain within a protein?

Accepted Answer

The pK$_a$ can be raised or lowered depending on nearby charges.

Question 20

A peptide is synthesized in the laboratory and is found to have a blocked N-terminus. Which of the following modifications could be responsible for this?

Accepted Answer

N-formylation

Amino Acids and the Primary Structure of Proteins

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