Question 1

Which of the following statements best explains why only L-amino acids are incorporated into proteins in living organisms on Earth?

Accepted Answer

The ribosomal machinery specifically recognizes the stereochemistry of L-amino acids during protein synthesis.

Question 2

A mutation in the gene encoding a protein changes a single amino acid from glutamate to valine. This change is most likely to affect which level of protein structure first?

Accepted Answer

Primary structure

Question 3

Which of the following interactions is primarily responsible for the formation of an α-helix in a protein's secondary structure?

Accepted Answer

Hydrogen bonds between backbone N-H and C=O groups

Question 4

Which of the following best describes the difference between the structures of cysteine and homocysteine, as shown in the provided image?

Accepted Answer

Homocysteine has an additional methylene (-CH2-) group in its side chain compared to cysteine.

Question 5

Which of the following bonds is formed during the condensation reaction that links two amino acids together?

Accepted Answer

Peptide bond

Question 6

A protein is found to consist of two α subunits and two β subunits. Which level of protein structure does this describe?

Accepted Answer

Quaternary structure

Question 7

Which of the following is a real-world example of the importance of protein folding, as demonstrated by Anfinsen’s experiment?

Accepted Answer

The ability of ribonuclease to regain catalytic activity after denaturation and renaturation in vitro

Question 8

Which of the following best explains why proline is often found at the turns of polypeptide chains and disrupts α-helix formation?

Accepted Answer

Proline lacks a hydrogen atom on its nitrogen, preventing it from participating in backbone hydrogen bonding.

Question 9

Which of the following types of bonds or interactions is NOT involved in stabilizing the tertiary structure of proteins?

Accepted Answer

Peptide bonds

Question 10

A patient is diagnosed with a disease caused by the accumulation of misfolded proteins in neurons, leading to neurodegeneration. Which process is most likely defective in this patient?

Accepted Answer

Chaperone-mediated protein folding and proteasome-mediated degradation

Question 11

Which of the following best describes the role of chaperone proteins in the cell?

Accepted Answer

They assist in the proper folding of newly synthesized polypeptides and refolding of misfolded proteins.

Question 12

Which of the following statements about the directionality of polypeptides is correct?

Accepted Answer

Polypeptides are synthesized from the N-terminus to the C-terminus.

Question 13

Which of the following is a consequence of the antiparallel arrangement of DNA strands in the double helix?

Accepted Answer

Hydrogen bonds can form between complementary bases with precise spacing.

Question 14

Which of the following best explains why DNA is more stable than RNA?

Accepted Answer

DNA lacks a 2' hydroxyl group, making its phosphodiester bonds less susceptible to hydrolysis.

Question 15

Which of the following is a correct complementary RNA sequence for the DNA template strand 3'-TACGGA-5'?

Accepted Answer

5'-AUGCCU-3'

Question 16

Which of the following best describes the difference between α-glucose and β-glucose?

Accepted Answer

The orientation of the hydroxyl group on the anomeric carbon differs between the two forms.

Question 17

Which of the following best explains why mammals cannot digest cellulose?

Accepted Answer

Mammals lack enzymes that can hydrolyze β(1→4) glycosidic bonds in cellulose.

Question 18

Which of the following statements about the structure and function of phospholipids in the plasma membrane is correct?

Accepted Answer

Phospholipids are amphipathic, with hydrophilic heads and hydrophobic tails, allowing them to form bilayers in aqueous environments.

Question 19

During prolonged exercise, such as marathon running, what is the primary role of lipids in energy metabolism?

Accepted Answer

They provide a steady, long-lasting energy supply after glycogen stores are depleted.

Question 20

Which of the following best describes the physiological role of high-density lipoprotein (HDL) in the body?

Accepted Answer

HDL enhances removal of cholesterol from tissues and transports it to the liver for excretion.

The Macromolecules of the Cell: Proteins, Nucleic Acids, Polysaccharides, and Lipids

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