Question 1

Which of the following best describes a zwitterion at physiological pH?

Accepted Answer

A molecule with both positive and negative charges, resulting in a net neutral charge.

Question 2

Which amino acid contains a side chain that can form disulfide bonds, contributing to protein tertiary structure?

Accepted Answer

Cysteine

Question 3

A conservative mutation in a gene changes the codon for glutamic acid (Glu, acidic) to aspartic acid (Asp, acidic). What is the likely effect on the protein?

Accepted Answer

Minimal effect, as both amino acids are acidic and similar in size.

Question 4

Which technique would be most appropriate for separating proteins based on their net charge at a given pH?

Accepted Answer

Ion exchange chromatography

Question 5

Given the peptide sequence Ala-Gly-Ser, which bond is considered the peptide bond?

Accepted Answer

The bond between the carboxyl group of Ala and the amino group of Gly.

Question 6

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

Accepted Answer

Leucine

Question 7

What is the isoelectric point ($$pI) of $$glycine, given its $$pK_a$$ values: $$pK_{a1} = 2.3 ($$carboxyl group) and $$pK_{a2} = 9.6 ($$amino group)?

Accepted Answer

$$pI = \frac{2.3 + 9.6}{2} = 5.95$$

Question 8

A protein is purified using affinity chromatography. Which property is most critical for the separation?

Accepted Answer

Specific binding affinity between the protein and the immobilized ligand.

Question 9

Which of the following best describes a Fischer projection?

Accepted Answer

A two-dimensional representation of a molecule where horizontal lines represent bonds projecting out of the plane and vertical lines represent bonds going behind the plane.

Question 10

Which of the following amino acids is aromatic?

Accepted Answer

Phenylalanine

Question 11

A non-conservative mutation changes a codon for valine (non-polar) to glutamate (acidic). What is the most likely consequence?

Accepted Answer

Altered protein folding due to a change in side chain properties.

Question 12

Which of the following is the correct one-letter code for the amino acid tryptophan?

Accepted Answer

W

Question 13

In SDS-PAGE, proteins are separated primarily based on which property?

Accepted Answer

Molecular weight

Question 14

Which of the following best describes the main chain of a peptide?

Accepted Answer

The backbone structure formed by repeating N-C-C units, excluding side chains.

Question 15

A gene sequence contains an open reading frame (ORF). What does this indicate?

Accepted Answer

A stretch of DNA that can be translated into a protein.

Question 16

Which of the following amino acids is most likely to be found at the active site of an enzyme due to its ability to participate in acid-base catalysis?

Accepted Answer

Histidine

Question 17

Which property of proteins is exploited in size exclusion chromatography?

Accepted Answer

Molecular size

Question 18

Which of the following statements about chiral carbon atoms is correct?

Accepted Answer

A chiral carbon is attached to four different groups and can exist as non-superimposable mirror images.

Question 19

Which of the following is a non-polar, aliphatic amino acid?

Accepted Answer

Isoleucine

Question 20

A protein sample is loaded onto an ion exchange column at pH 7.0. The protein has a $$pI of 5.0. $$What will happen?

Accepted Answer

The protein will have a net negative charge and bind to an anion exchange resin.

Fundamental Concepts in Biochemistry: Amino Acids, Peptides, and Protein Purification

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