Question 1

Which of the following best describes a zwitterion form of an amino acid at its isoelectric point (pI)?

Accepted Answer

It has both a positively charged amino group and a negatively charged carboxyl group, resulting in a net charge of zero.

Question 2

Which amino acid would be classified as polar (neutral) based on its side chain?

Accepted Answer

Serine

Question 3

A patient’s blood pH drops significantly below the isoelectric point of glycine (pI = 6.0). What is the predominant form of glycine in this acidic environment?

Accepted Answer

Glycine has a net positive charge due to protonation of the carboxyl group.

Question 4

Which type of interaction is primarily responsible for stabilizing the secondary structure of an alpha helix in proteins?

Accepted Answer

Hydrogen bonds between the carbonyl oxygen and the amide hydrogen of the peptide backbone

Question 5

Which of the following best describes the quaternary structure of a protein?

Accepted Answer

The arrangement and interaction of multiple polypeptide subunits in a functional protein complex

Question 6

Which of the following is a real-life example of protein denaturation?

Accepted Answer

The solidification of egg whites when heated during cooking

Question 7

Which enzyme class catalyzes the transfer of a phosphate group from ATP to glucose?

Accepted Answer

Transferases

Question 8

A competitive inhibitor of an enzyme:

Accepted Answer

Has a structure similar to the substrate and competes for the active site; its effect can be reversed by increasing substrate concentration.

Question 9

Which of the following best explains why enzymes are highly specific for their substrates?

Accepted Answer

The active site of the enzyme has a unique three-dimensional shape that only fits specific substrates.

Question 10

Which of the following statements about enzyme activity and temperature is correct?

Accepted Answer

Enzyme activity is highest at the optimum temperature and decreases at higher temperatures due to denaturation.

Question 11

Which of the following amino acids would be most likely to participate in a salt bridge within a protein’s tertiary structure?

Accepted Answer

Aspartic acid and lysine

Question 12

A peptide bond is formed between which two functional groups of adjacent amino acids?

Accepted Answer

The amino group of one and the carboxyl group of the next

Question 13

Which of the following best describes the effect of a noncompetitive inhibitor on an enzyme-catalyzed reaction?

Accepted Answer

It binds to a different site on the enzyme, changing the enzyme’s shape and reducing activity, and cannot be overcome by adding more substrate.

Question 14

Which of the following is a function of globular proteins in the human body?

Accepted Answer

Transporting oxygen in muscle tissue

Question 15

Which of the following best explains why hemoglobin is considered to have quaternary structure?

Accepted Answer

It consists of multiple polypeptide subunits (two alpha and two beta chains) that function together.

Question 16

Which of the following best describes the induced-fit model of enzyme action?

Accepted Answer

The enzyme and substrate adjust their shapes slightly to achieve a better fit, enhancing catalysis.

Question 17

Which of the following laboratory procedures is most likely to cause denaturation of a protein?

Accepted Answer

Heating the protein solution to 80°C

Question 18

Which of the following best describes the role of enzymes in biochemical reactions?

Accepted Answer

They lower the activation energy, increasing the rate of reaction.

Question 19

Which of the following is a diagnostic use of enzymes in medicine?

Accepted Answer

Measuring the activity of creatine kinase (CK) to assess heart attack severity

Amino Acids, Proteins, and Enzymes: Structure, Function, and Mechanisms

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