Question 1

Which of the following best describes the four components of an amino acid and their roles in protein structure?

Accepted Answer

A central carbon atom bonded to a hydrogen atom, an amino group, a carboxyl group, and a variable R group, where the R group determines the amino acid's unique properties.

Question 2

Which type of bond is responsible for linking amino acids together in a polypeptide chain?

Accepted Answer

Peptide bond

Question 3

A mutation causes a single amino acid substitution in the primary structure of hemoglobin, resulting in sickle-cell disease. Which level of protein structure is directly altered by this mutation, and what is the likely consequence?

Accepted Answer

Primary structure; it changes the sequence of amino acids, which can alter the protein's overall shape and function.

Question 4

Which of the following interactions is NOT a type of noncovalent bond that helps stabilize the tertiary structure of a protein?

Accepted Answer

Peptide bonds

Question 5

A protein is exposed to high heat, causing it to lose its three-dimensional structure and function. Which process has occurred, and which levels of protein structure are most affected?

Accepted Answer

Denaturation; secondary, tertiary, and quaternary structures are disrupted, but the primary structure remains intact.

Question 6

Which of the following best explains why proteins can perform such a wide variety of functions in cells?

Accepted Answer

Proteins have diverse structures due to the 20 different amino acids and their unique R groups, allowing for a vast array of shapes and chemical properties.

Question 7

Which of the following amino acids would most likely be found in the interior of a globular protein, away from water?

Accepted Answer

Leucine, because it has a nonpolar R group.

Question 8

Which of the following best describes the difference between a polypeptide and a protein?

Accepted Answer

A polypeptide is a single linear chain of amino acids, while a protein is one or more polypeptides folded into a functional structure.

Question 9

Which of the following best explains why a change in pH can disrupt protein structure?

Accepted Answer

A change in pH can alter the ionization state of acidic and basic R groups, disrupting ionic bonds and hydrogen bonds that stabilize the protein's structure.

Question 10

Which of the following is an example of a protein's function as an enzyme?

Accepted Answer

Catalyzing the hydrolysis of sucrose into glucose and fructose.

Question 11

Which of the following best describes the formation of a peptide bond?

Accepted Answer

A dehydration reaction between the carboxyl group of one amino acid and the amino group of another, releasing $\mathrm{H_2O}$.

Question 12

A protein is composed of two identical alpha subunits and two identical beta subunits. What is the best term to describe this protein's structure?

Accepted Answer

A heterotetramer with quaternary structure.

Question 13

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

Accepted Answer

It is stabilized by hydrogen bonds between backbone atoms, forming alpha-helices and beta-sheets.

Question 14

Which of the following best explains why a protein's tertiary structure is important for its function?

Accepted Answer

The tertiary structure determines the overall three-dimensional shape of the protein, which is critical for binding to other molecules and performing its specific function.

Question 15

Which of the following scenarios best illustrates the importance of both covalent and noncovalent bonds in protein structure?

Accepted Answer

The peptide bonds form the backbone of the protein (covalent), while hydrogen bonds, ionic interactions, and hydrophobic interactions (noncovalent) stabilize its folded shape.

Question 16

A scientist is studying a protein that loses its function when a single amino acid with a charged R group is replaced by one with a nonpolar R group. Which of the following is the most likely explanation?

Accepted Answer

The replacement disrupts ionic interactions or hydrogen bonds that are critical for the protein's structure or function.

Question 17

Which of the following best describes the role of water in the folding of globular proteins?

Accepted Answer

Water promotes the burial of hydrophobic R groups in the protein's interior, stabilizing the folded structure.

Question 18

Which of the following is a correct statement about the quaternary structure of proteins?

Accepted Answer

It involves the association of two or more polypeptide subunits to form a functional protein complex.

Question 19

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

Accepted Answer

The three-dimensional shape of the enzyme's active site is complementary to the shape of its substrate, allowing precise binding.

Building Biological Molecules: Proteins – Structure, Function, and Amino Acids

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