Q: A researcher wants to estimate the number of amino acid residues in a protein with a molecular weight of 44,000 Da. Which equation should they use?

$$\text{Number of residues} = \frac{\text{Molecular weight}}{110}$$

Question 1

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

Accepted Answer

The linear sequence of amino acids joined by peptide bonds.

Question 2

Amino acids are classified based on the properties of their R groups. Which class of amino acids would most likely be found in the interior of a globular protein in aqueous solution?

Accepted Answer

Nonpolar, aliphatic

Question 3

Which of the following equations correctly represents the calculation of the isoelectric point ($$pI) $$for an amino acid without an ionizable side chain?

Accepted Answer

$$pI = \frac{pK_1$ + pK_2$}{2}$$

Question 4

During protein purification, which method would be most effective for separating proteins based on their size?

Accepted Answer

Size-exclusion chromatography

Question 5

Which of the following amino acids can form disulfide bonds, contributing to protein stability?

Accepted Answer

Cysteine

Question 6

A protein is found to have a net negative charge at physiological pH (7.0). Which of the following statements best explains this observation?

Accepted Answer

The protein has a $$pI$$ less than 7.0.

Question 7

Which of the following best describes the effect of sodium dodecyl sulfate (SDS) in SDS-PAGE electrophoresis?

Accepted Answer

It gives all proteins a similar charge-to-mass ratio, allowing separation by molecular weight.

Question 8

Which of the following modifications is an example of a post-translational modification that can regulate protein function?

Accepted Answer

Phosphorylation

Question 9

A peptide has the sequence Ala-Glu-Lys. Which of the following groups will be ionized at pH 7.0?

Accepted Answer

The alpha-amino group and the side chain of Glu

Question 10

Which of the following statements about protein purification is correct?

Accepted Answer

Ion-exchange chromatography separates proteins based on their net charge.

Question 11

Which of the following is a correct description of a conjugated protein?

Accepted Answer

A protein that contains a permanently associated non-amino acid component.

Question 12

Which of the following best explains why aromatic amino acids absorb ultraviolet light at 270–280 nm?

Accepted Answer

Their side chains contain conjugated double bonds.

Question 13

A researcher wants to estimate the number of amino acid residues in a protein with a molecular weight of 44,000 Da. Which equation should they use?

Accepted Answer

$$	ext{Number of residues} = \frac{	ext{Molecular weight}}{110}$$

Question 14

Which of the following statements about the D, L system for amino acids is correct?

Accepted Answer

Proteins in living organisms are constructed from L-amino acids.

Question 15

Which of the following best describes the role of mass spectrometry in protein analysis?

Accepted Answer

It measures the molecular mass and can provide sequence information.

Question 16

Which of the following is a real-world example of horizontal gene transfer affecting protein evolution?

Accepted Answer

The rapid spread of antibiotic-resistance genes in bacterial populations.

Question 17

Which of the following best describes a zwitterion?

Accepted Answer

A molecule with both positive and negative charges but a net charge of zero.

Question 18

Which of the following statements about peptide bonds is correct?

Accepted Answer

Peptide bonds are covalent bonds formed by condensation reactions.

Question 19

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

Accepted Answer

It has a side chain that is a hydrogen atom, making it achiral.

Amino Acids, Peptides, and Proteins: Structure, Properties, and Biochemical Techniques

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