Question 1

Which of the following best describes the structure of an α-amino acid as shown in the first image?

Accepted Answer

A central carbon atom bonded to an amino group, a carboxylic acid group, a hydrogen atom, and a variable R group.

Question 2

What is the effect of lowering the pH to 0 on the structure of an α-amino acid?

Accepted Answer

The carboxylate group ($$\mathrm{COO^-}) $$accepts a proton to become $$\mathrm{COOH}$$, resulting in a positively charged ion.

Question 3

Which equation represents the reaction of an α-amino acid in a basic environment?

Accepted Answer

$$\mathrm{RCH(NH_3$^+)COO^- + OH^- \rightarrow RCH(NH_2$)COO^- + H_2O}$$

Question 4

Which of the following statements about peptide bonds is correct?

Accepted Answer

Peptide bonds have partial double-bond character due to resonance, restricting free rotation.

Question 5

What is the main reason that most peptide bonds in proteins are found in the trans configuration?

Accepted Answer

Steric strain between the R groups is minimized in the trans configuration.

Question 6

How many constitutional isomers are possible for a pentapeptide made from five different α-amino acids?

Accepted Answer

120

Question 7

Which of the following best describes a zwitterion?

Accepted Answer

A molecule with both a positive and a negative charge on different atoms, but overall neutral.

Question 8

At the isoelectric point (pI) of an amino acid, which statement is true?

Accepted Answer

The amino acid exists predominantly as a zwitterion.

Question 9

Which of the following is NOT a function of proteins in living organisms?

Accepted Answer

Storing genetic information

Question 10

Which force is NOT involved in stabilizing the tertiary structure of proteins?

Accepted Answer

Peptide bond formation

Question 11

Which of the following best describes the secondary structure of proteins?

Accepted Answer

Regular repeating patterns such as α-helix and β-pleated sheet stabilized by hydrogen bonds.

Question 12

What is the main stabilizing force in the α-helix structure of proteins?

Accepted Answer

Intramolecular hydrogen bonds between backbone C=O and N-H groups.

Question 13

Which of the following statements about quaternary structure is correct?

Accepted Answer

Quaternary structure refers to the arrangement of multiple polypeptide chains in a protein.

Question 14

Which protein is an example of a conjugated protein, and what is its prosthetic group?

Accepted Answer

Hemoglobin; heme group

Question 15

What happens to the structure of collagen when it is boiled?

Accepted Answer

The triple helix disappears and the molecules adopt a random coil conformation, forming gelatin.

Question 16

Which of the following is a characteristic of fibrous proteins?

Accepted Answer

They are insoluble in water and mainly serve structural purposes.

Question 17

Which amino acid side chain is most likely to participate in hydrophobic interactions?

Accepted Answer

Valine

Question 18

Which of the following best explains why proteins denature when heated?

Accepted Answer

Heat disrupts hydrogen bonds, causing the loss of secondary and tertiary structure.

Question 19

Integral membrane proteins are stabilized in the lipid bilayer primarily by which structural feature?

Accepted Answer

Nonpolar outer surfaces interacting with the lipid bilayer.

Question 20

Which of the following is a multi-step process that occurs during the synthesis of a peptide from α-amino acids?

Accepted Answer

Dehydration reaction between the carboxyl group of one amino acid and the amino group of another, forming a peptide bond.

Proteins and Amino Acids: Structure, Function, and Biochemistry

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