Q: Which of the following statements about the $$b-$$helix is correct?

The $$b-$$helix has 3.6 residues per turn and hydrogen bonds form between the carbonyl oxygen of residue $$i$$ and the amide hydrogen of residue $$i+4.$$

Question 1

Which of the following functional groups is most likely to act as a hydrogen bond donor in a protein structure?

Accepted Answer

An amine group ($$\mathrm{-NH_2$})$$

Question 2

Which of the following best explains why hydrophobic interactions are promoted in aqueous environments?

Accepted Answer

The aggregation of hydrophobic molecules releases ordered water molecules, increasing the entropy of the system.

Question 3

Given the following acid dissociation reaction: $$\mathrm{HA \rightleftharpoons H^+ + A^-}$$, which of the following is the correct expression for the acid dissociation constant ($$K_a$$)?

Accepted Answer

$$K_a = \dfrac{[H^+][A^-]}{[HA]}$$

Question 4

A solution contains 0.1 M acetic acid ($$pK_a = 4.76) $$and 0.1 M sodium acetate. What is the pH of the solution? (Use the Henderson-Hasselbalch equation: $$pH = pK_a + \log_{10}\left(\dfrac{[A^-]}{[HA]}\right))$$

Accepted Answer

pH = 4.76

Question 5

Which of the following statements about the isoelectric point ($$pI) of an $$amino acid is correct?

Accepted Answer

At the $$pI$$, the amino acid is least soluble in water.

Question 6

Which of the following best describes the relationship between free energy ($$\Delta G$$), enthalpy ($$\Delta H$$), and entropy ($$\Delta S) at $$constant temperature?

Accepted Answer

$$\Delta G = \Delta H - T\Delta S$$

Question 7

A biochemical reaction has $$\Delta G^\circ' = +5 kJ/$$mol. Which of the following strategies could make this reaction proceed spontaneously in a cell?

Accepted Answer

Couple the reaction to a second reaction with a large negative $$\Delta G^\circ'$$ such that the sum is negative.

Question 8

Which of the following is true regarding the difference between $$K ($$equilibrium constant) and $$Q ($$reaction quotient) in a biochemical reaction?

Accepted Answer

$$K is $$calculated using equilibrium concentrations, while $$Q$$ uses current (not necessarily equilibrium) concentrations.

Question 9

Which of the following best describes an oxidation reaction in biochemistry?

Accepted Answer

A molecule loses electrons.

Question 10

Given the standard reduction potentials: $$E^\circ'(A/A^-) = -0.32 V $$and $$E^\circ'(B/B^-) = +0.82 V$$, what is the standard free energy change ($$\Delta G^\circ') $$for the reaction $$A^- + B \rightarrow A + B^-$$? (Use $$\Delta G^\circ' = -nF\Delta E^\circ'$$, $$n=1$$, $$F=96,485 C/$$mol)

Accepted Answer

$$\Delta G^\circ' = -110 kJ/$$mol

Question 11

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

Accepted Answer

Leucine

Question 12

A peptide bond is formed by a condensation reaction between which two functional groups of adjacent amino acids?

Accepted Answer

Amino group and carboxyl group

Question 13

Which of the following statements about the $$b-$$helix is correct?

Accepted Answer

The $$b-$$helix has 3.6 residues per turn and hydrogen bonds form between the carbonyl oxygen of residue $$i$$ and the amide hydrogen of residue $$i+4.$$

Question 14

Which of the following best describes the Ramachandran plot?

Accepted Answer

A plot of the allowed values of the backbone dihedral angles $$\phi$$ and $$\psi in a $$polypeptide.

Question 15

Which of the following best describes the difference between a protein monomer and a homo-oligomer?

Accepted Answer

A monomer is a single polypeptide chain, while a homo-oligomer is composed of multiple identical polypeptide chains.

Question 16

Which of the following statements about myoglobin and hemoglobin is correct?

Accepted Answer

Hemoglobin exhibits cooperative binding of oxygen, while myoglobin does not.

Question 17

Which of the following is an example of an allosteric effector of hemoglobin?

Accepted Answer

2,3-Bisphosphoglycerate (2,3-BPG)

Question 18

Which of the following best describes the role of collagen in organisms?

Accepted Answer

Collagen is a fibrous protein that provides structural support in connective tissues.

Question 19

A polypeptide has the sequence Glu-Lys-Ala. Given the $$pK_a$$ values: Glu side chain = 4.1, Lys side chain = 10.5, N-terminus = 9.0, C-terminus = 2.0. What is the approximate isoelectric point ($$pI) of $$this peptide?

Accepted Answer

$$pI = \dfrac{4.1 + 9.0}{2} = 6.55 ($$using the $$pK_a$$ values that flank the neutral species)

BCH 351 Exam 1 Study Guide: Foundations of Biochemistry and Protein Structure

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