Question 1

Which of the following best describes the structure of an amino acid in its ionized form at physiological pH?

Accepted Answer

A central carbon atom bonded to a hydrogen atom, an amino group ($$\mathrm{NH_3$^+}$$), a carboxyl group ($$\mathrm{COO^-}$$), and an R group.

Question 2

During protein synthesis, which type of bond forms between amino acids, and what is the chemical reaction that creates this bond?

Accepted Answer

Peptide bond; condensation reaction

Question 3

Which of the following statements about the primary structure of a protein is correct?

Accepted Answer

It refers to the sequence of amino acids linked by peptide bonds.

Question 4

A single amino acid substitution in the primary structure of hemoglobin can lead to sickle cell disease. This is an example of:

Accepted Answer

A change in primary structure affecting protein function

Question 5

Which of the following interactions is NOT involved in stabilizing the tertiary structure of a protein?

Accepted Answer

Peptide bonds between amino acids

Question 6

Which level of protein structure is directly responsible for the formation of alpha helices and beta-pleated sheets?

Accepted Answer

Secondary structure

Question 7

A protein is found to consist of two identical polypeptide subunits. What is the best description of its quaternary structure?

Accepted Answer

Dimer and homodimer

Question 8

Which of the following best explains why proteins are considered the most diverse biological molecules?

Accepted Answer

They are involved in all cellular processes and have a wide variety of structures and functions.

Question 9

Which of the following is a function of proteins in living organisms?

Accepted Answer

All of the above

Question 10

A scientist mutates a gene so that a hydrophobic amino acid in a protein is replaced by a hydrophilic one. Which level(s) of protein structure could be affected by this change?

Accepted Answer

Primary, secondary, tertiary, and quaternary structures

Question 11

Which of the following correctly matches the protein structure level with its stabilizing interaction?

Accepted Answer

Tertiary structure – R group interactions

Question 12

Which of the following best describes the directionality of a polypeptide chain?

Accepted Answer

It runs from the N-terminus to the C-terminus.

Question 13

Which of the following is an example of a covalent bond that stabilizes protein tertiary structure?

Accepted Answer

Disulfide bond ($$\mathrm{S-S}) $$between cysteine residues

Question 14

A protein loses its function after being exposed to high heat. Which structural level is most likely disrupted first?

Accepted Answer

Secondary structure

Question 15

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

Accepted Answer

It includes alpha helices and beta-pleated sheets stabilized by hydrogen bonds.

Question 16

Which of the following best explains why enzymes are effective biological catalysts?

Accepted Answer

They bind substrates at a specific location called the active site, lowering the activation energy of reactions.

Question 17

Which of the following is NOT a function of proteins?

Accepted Answer

Storing genetic information

Question 18

A protein is composed of four different polypeptide subunits, each with a unique sequence. What is the best description of its quaternary structure?

Accepted Answer

Heterotetramer

Question 19

Which of the following interactions is most likely to occur between the side chains of lysine and aspartic acid in a protein's tertiary structure?

Accepted Answer

Ionic bond

Question 20

Which of the following best describes the process by which amino acids are joined to form a polypeptide?

Accepted Answer

A condensation reaction forms a peptide bond, releasing a molecule of water ($$\mathrm{H_2O}).$$

Protein Structure and Function: Study Notes for General Biology

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