Question 1

Which property of water is most critical for its role as the 'medium of life' in biological systems?

Accepted Answer

Its ability to form hydrogen bonds, leading to high cohesion and solvent properties

Question 2

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.

Accepted Answer

$$pH = 4.76$$

Question 3

Which of the following best describes the peptide bond formed between two amino acids?

Accepted Answer

A covalent bond formed by the reaction of the amino group of one amino acid with the carboxyl group of another, releasing water

Question 4

Which of the following statements about the chirality of amino acids is correct?

Accepted Answer

Glycine is the only achiral amino acid

Question 5

During protein sequencing, which reagent is commonly used to selectively label the N-terminal amino acid?

Accepted Answer

Edman reagent (phenylisothiocyanate)

Question 6

Which level of protein structure is primarily stabilized by hydrogen bonds between backbone amide and carbonyl groups?

Accepted Answer

Secondary structure

Question 7

A patient is diagnosed with sickle cell anemia, which is caused by a single amino acid substitution in hemoglobin. This mutation affects which level of protein structure first?

Accepted Answer

Primary structure

Question 8

Which of the following best describes the effect of a competitive inhibitor on enzyme kinetics?

Accepted Answer

Increases $$K_m$$ and does not affect $$V_{max}$$

Question 9

Which equation describes the relationship between pH, pKa, and the ratio of conjugate base to acid in a buffer system?

Accepted Answer

$$pH = pK_a + \log_{10} \left( \frac{[A^-]}{[HA]} \right)$$

Question 10

A protein is found to have four identical subunits. Which level of protein structure does this describe?

Accepted Answer

Quaternary structure

Question 11

Which of the following is a correct statement about enzyme-catalyzed reactions?

Accepted Answer

Enzymes lower the activation energy ($$\Delta G$$^{\ddagger}$$) but do not change the overall free energy change ($$\Delta G$$) of the reaction

Question 12

A researcher is studying the titration curve of glycine. At the isoelectric point ($$pI$$), which of the following is true?

Accepted Answer

The net charge of glycine is zero

Question 13

Which of the following is an example of allosteric regulation of enzyme activity?

Accepted Answer

Binding of a molecule at a site other than the active site, causing a conformational change

Question 14

Which of the following best explains why proteins fold spontaneously in aqueous environments?

Accepted Answer

The hydrophobic effect drives nonpolar side chains to the protein interior, increasing entropy of water

Question 15

A Lineweaver-Burk plot of an enzyme-catalyzed reaction in the presence of a noncompetitive inhibitor will show:

Accepted Answer

An increase in the y-intercept and no change in the x-intercept

Question 16

Which of the following experimental methods is most suitable for determining the primary sequence of a protein?

Accepted Answer

Edman degradation

Question 17

Which of the following statements about the secondary structure of proteins is correct?

Accepted Answer

Alpha helices and beta sheets are stabilized by hydrogen bonds between backbone atoms

Question 18

A mutation causes an enzyme to lose its ability to be regulated by phosphorylation. Which type of regulation is most directly affected?

Accepted Answer

Covalent modification

Question 19

Which of the following best describes the relationship between $$K_m$$ and enzyme-substrate affinity?

Accepted Answer

A lower $$K_m$$ indicates higher affinity between enzyme and substrate

Question 20

A patient is given a drug that acts as a noncompetitive inhibitor of an essential metabolic enzyme. What is the expected effect on $$V_{max}$$ and $$K_m$$?

Accepted Answer

$$V_{max}$$ decreases, $$K_m$$ remains unchanged

Biochemistry I: Core Concepts and Protein Structure

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