Question 1

Which of the following amino acids is classified as aromatic and has a side chain that can participate in stacking interactions?

Accepted Answer

Phenylalanine

Question 2

A peptide has the sequence Ala-Gly-Cys. Which terminus is written first in standard notation, and what is the correct orientation?

Accepted Answer

Amino terminus first, written as Ala-Gly-Cys

Question 3

Which equation is used to calculate the pH of a buffer solution containing a weak acid and its conjugate base?

Accepted Answer

$$\mathrm{pH} = \mathrm{pK_a} + \log\left(\frac{[A^-]}{[HA]}\right) $$

Question 4

Which property of the peptide bond is primarily responsible for its rigidity and planarity?

Accepted Answer

Partial double bond character due to resonance

Question 5

A protein is purified using ion exchange chromatography. Which property of the protein is most important for separation in this technique?

Accepted Answer

Net charge at the working pH

Question 6

Which reagent is used to identify the N-terminal amino acid in a peptide, and what is the product formed?

Accepted Answer

2,4-dinitrofluorobenzene (DNFB), forming a dinitrophenyl derivative

Question 7

Trypsin is an endopeptidase used in protein sequencing. Where does trypsin cleave peptide bonds?

Accepted Answer

On the carboxy side of lysine and arginine

Question 8

Which structural feature is characteristic of collagen and contributes to its tensile strength?

Accepted Answer

Triple helical structure with frequent glycine and proline residues

Question 9

A protein sample is analyzed by SDS-PAGE. What is the primary role of SDS in this technique?

Accepted Answer

To denature proteins and impart a uniform negative charge

Question 10

Which of the following best describes the quaternary structure of hemoglobin?

Accepted Answer

Four polypeptide chains, two alpha and two beta, forming two alpha/beta dimers

Question 11

Which effect describes the increase in oxygen affinity of hemoglobin as more oxygen molecules bind?

Accepted Answer

Hill effect (cooperativity)

Question 12

A solution contains a weak acid with a pKa of 4.5. If the ratio $$\frac{[A^-]}{[HA]} is 10$$, what is the pH?

Accepted Answer

$$\mathrm{pH} = 4.5 + \log(10) = 5.5 $$

Question 13

Which of the following best explains why proteins with many non-polar residues are less soluble in water?

Accepted Answer

Non-polar residues cannot form favorable interactions with water, leading to aggregation via the hydrophobic effect

Question 14

Which of the following is a correct statement about the Ramachandran plot?

Accepted Answer

It displays the possible conformations of peptide bonds based on phi and psi angles

Question 15

Which factor favors the T (tense) form of hemoglobin, promoting oxygen release to tissues?

Accepted Answer

Low pH and high 2,3-BPG concentration

Question 16

Which intermolecular force is primarily responsible for stabilizing the alpha helix in proteins?

Accepted Answer

Hydrogen bonding between backbone amide and carbonyl groups

Question 17

A protein contains several disulfide bridges. Which reagent would you use to reduce these bridges, and why is it important to block sulfhydryl groups afterward?

Accepted Answer

Mercaptoethanol; blocking prevents re-oxidation and incorrect disulfide formation

Question 18

Which of the following best describes the effect of 2,3-BPG on hemoglobin's oxygen binding curve?

Accepted Answer

It shifts the curve to the right, decreasing oxygen affinity

Question 19

Which of the following is an example of a protein with a prosthetic group, and what is the group?

Accepted Answer

Hemoglobin with a heme group

Question 20

A protein sample is subjected to size exclusion chromatography. Which property determines the order of elution?

Accepted Answer

Proteins with larger molecular weight elute first

Amino Acids, Proteins, and Hemoglobin: Structure, Properties, and Function

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