Question 1

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

Accepted Answer

The sequence of amino acids in a polypeptide chain, linked by peptide bonds.

Question 2

A mutation in the gene encoding a protein changes a codon from GAA to GAG. Both codons code for glutamic acid. What is the most likely effect of this mutation on the protein's function?

Accepted Answer

It will have no effect on the protein's function because the amino acid sequence remains unchanged.

Question 3

Which of the following amino acids contains a sulfur atom in its side chain?

Accepted Answer

Methionine

Question 4

At a pH above the isoelectric point ($$pI) of a $$peptide, what is the net charge on the peptide?

Accepted Answer

Negative

Question 5

Which of the following best explains why insulin is synthesized as preproinsulin in the cell?

Accepted Answer

To allow for rapid mobilization of active insulin when needed by storing it as an inactive precursor.

Question 6

Which of the following codons is a start codon in the standard genetic code?

Accepted Answer

AUG

Question 7

A researcher is purifying a His-tagged protein using immobilized metal affinity chromatography (IMAC). Which molecule is most likely used to elute the His-tagged protein from the column?

Accepted Answer

Imidazole

Question 8

Which of the following best describes a conservative amino acid substitution?

Accepted Answer

A mutation that replaces an amino acid with another of similar size and chemical property.

Question 9

During protein purification, which technique separates proteins based primarily on their size?

Accepted Answer

Size exclusion chromatography

Question 10

A protein has a $$pI of 5.0. If it is $$placed in a buffer at pH 7.0, what will be the net charge of the protein and which type of ion exchange resin would be best for its purification?

Accepted Answer

Net negative; anion exchange resin

Question 11

Which of the following is a correct representation of the peptide bond formed between two generic amino acids?

Accepted Answer

$$\mathrm{R_1$-CH(NH_2$)-CO-NH-CH(R_2$)-COOH}$$

Question 12

Which of the following best describes the relationship between sequence similarity and evolutionary relatedness in proteins such as cytochrome c?

Accepted Answer

Proteins with more similar sequences are more likely to be evolutionarily related.

Question 13

A peptide has the following sequence: Ala-Glu-Lys-Ser. At pH 7, which of the following best describes its net charge? (Assume N-terminus and C-terminus are free.)

Accepted Answer

+1

Question 14

Which of the following is a function of consensus sequences in protein families?

Accepted Answer

They identify the most highly conserved amino acid residues across multiple sequences.

Question 15

Which of the following best explains why DNA sequencing alone may not provide the complete primary structure of a protein such as insulin?

Accepted Answer

DNA sequencing does not reveal post-translational modifications.

Question 16

A researcher uses BLAST to compare the amino acid sequences of human myoglobin and human alpha-globin. Which of the following is most likely to be true?

Accepted Answer

The two proteins will have some sequence similarity, reflecting evolutionary divergence from a common ancestor.

Question 17

Which of the following best describes the role of a selection marker in a protein expression vector?

Accepted Answer

It allows only cells containing the vector to survive in the presence of an antibiotic.

Question 18

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

Accepted Answer

Glutamic acid

Question 19

A protein sample is loaded onto a cation exchange column at pH 6.0. The protein has a $$pI of 8.5. $$What will happen to the protein during chromatography?

Accepted Answer

It will bind to the column because it is positively charged at pH 6.0.

Question 20

Which of the following best explains why post-translational modifications are important for protein function?

Accepted Answer

They can alter the protein's activity, stability, localization, or interactions with other molecules.

Introduction to Proteins: The Primary Level of Protein Structure

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