Question 1

Which of the following amino acids is classified as aromatic and has a side chain that can participate in hydrogen bonding due to a hydroxyl group?

Accepted Answer

Tyrosine

Question 2

At pH 7.0, what is the predominant charge state of glutamic acid (Glu, E)? The side chain pKa is approximately 4.1.

Accepted Answer

Net charge of -1

Question 3

Given the peptide sequence Ala-Gly-Lys, what is the expected net charge at pH 12? (Assume N-terminus pKa = 9.5, C-terminus pKa = 2.0, Lys side chain pKa = 10.5)

Accepted Answer

$$-1$$

Question 4

Which of the following best describes the peptide bond in proteins?

Accepted Answer

It is a planar bond due to partial double-bond character, restricting rotation.

Question 5

A protein mixture is loaded onto a size-exclusion chromatography column. Which protein will elute first?

Accepted Answer

The largest protein

Question 6

Which of the following statements about SDS-PAGE is correct?

Accepted Answer

Proteins are separated based on their size, with smaller proteins migrating further.

Question 7

A peptide has the sequence Ser-Glu-Arg. What is the one-letter code for this peptide?

Accepted Answer

S-E-R

Question 8

Which of the following best describes a zwitterion?

Accepted Answer

A molecule with both positive and negative charges but is overall neutral

Question 9

A mutation changes a codon from GAA (Glu) to GCA (Ala). This is an example of:

Accepted Answer

A non-conservative mutation

Question 10

Which of the following best describes the main chain (backbone) of a polypeptide?

Accepted Answer

It includes all atoms except the side chains.

Question 11

You are purifying a protein with a net positive charge at pH 7.0. Which chromatography method would best retain this protein on the column?

Accepted Answer

Cation exchange chromatography (CM)

Question 12

Which of the following is true regarding the coding and non-coding strands of DNA?

Accepted Answer

The coding strand matches the mRNA sequence (except T/U).

Question 13

A protein binds specifically to ATP. Which purification technique would best isolate this protein from a mixture?

Accepted Answer

Affinity chromatography using ATP-linked beads

Question 14

Which of the following amino acids is most likely to be found at the N-terminus of a newly synthesized protein?

Accepted Answer

Methionine

Question 15

Calculate the isoelectric point ($$pI) of $$glycine, given that $$pK_1 ($$carboxyl) = 2.3 and $$pK_2 ($$amino) = 9.6.

Accepted Answer

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

Question 16

Which of the following best describes a conservative mutation?

Accepted Answer

A mutation that changes an amino acid to one with similar properties

Question 17

A protein sample is loaded onto an anion exchange column (DEAE) at pH 8.0. Which protein will elute first?

Accepted Answer

A protein with a net positive charge

Question 18

Which of the following is true about chiral centers in amino acids?

Accepted Answer

Glycine is the only achiral amino acid.

Question 19

You are given a DNA sequence. Which feature would you look for to identify a possible open reading frame (ORF)?

Accepted Answer

A region with a start codon, a stop codon, and sufficient intervening sequence

Question 20

Which of the following best describes a Fischer projection?

Accepted Answer

A depiction where horizontal bonds project toward the viewer and vertical bonds project away

Introduction to Proteins: The Primary Level of Protein Structure

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