Question 1

Which of the following statements best explains why proteins are able to perform such a wide variety of biological functions?

Accepted Answer

Proteins are linear, heteropolymers of amino acids with variable size and physical properties, resulting in diverse structures and functions.

Question 2

At which pH will half of the molecules in solution be in the monohydrogen phosphate form ($\mathrm{HPO_4^{2-}}$) and half in the phosphate form ($\mathrm{PO_4^{3-}}$)?

Accepted Answer

pH 12.3

Question 3

Which of the following best describes a zwitterion?

Accepted Answer

A molecule that contains an equal number of positively and negatively charged functional groups.

Question 4

Given the following pKa values: $\mathrm{pK_a,COOH} \approx 2$ and $\mathrm{pK_a,NH_3^+} \approx 9.5$, what is the net charge of a generic amino acid at pH 1?

Accepted Answer

+1

Question 5

Which two amino acids are structural isomers of one another?

Accepted Answer

Leucine and Isoleucine

Question 6

Which amino acid is achiral and why?

Accepted Answer

Glycine, because its side chain is a hydrogen atom.

Question 7

What is the isoelectric point ($pI$) of glycine, given $pK_{a,1} = 2.0$ and $pK_{a,2} = 9.5$?

Accepted Answer

$pI = 5.75$

Question 8

Which amino acid contains a sulfur atom in its side chain and can form disulfide bonds under oxidizing conditions?

Accepted Answer

Cysteine

Question 9

At a pH above its $pK_a$, an acidic functional group (e.g., $-COOH$) will be:

Accepted Answer

Predominantly in the deprotonated form ($-COO^-$)

Question 10

Which property is shared by all non-polar amino acids?

Accepted Answer

They all have hydrocarbon side chains and lack reactive functional groups.

Question 11

Which amino acid is most likely to be found at the active site of an enzyme due to its ability to act as both a proton donor and acceptor near physiological pH?

Accepted Answer

Histidine

Question 12

If aspartic acid is dissolved in water at pH 7, what will happen to the pH of the solution?

Accepted Answer

The pH will decrease because aspartic acid donates protons.

Question 13

Which amino acid has a side chain that can be phosphorylated and contains a hydroxyl group?

Accepted Answer

Threonine

Question 14

Which of the following amino acids is classified as aromatic and absorbs UV light strongly at 280 nm?

Accepted Answer

Tryptophan

Question 15

Which of the following best describes the CORN rule for L-amino acids?

Accepted Answer

Looking down the H–Cα bond, CO–R–N are arranged clockwise.

Question 16

Which amino acid is most likely to form a disulfide bond in an oxidizing environment?

Accepted Answer

Cysteine

Question 17

Which amino acid is most likely to be found in the interior of a globular protein due to its highly hydrophobic side chain?

Accepted Answer

Leucine

Question 18

Which of the following amino acids contains an amide functional group in its side chain?

Accepted Answer

Asparagine

Question 19

What is the net charge of a generic amino acid at pH 14, given $\mathrm{pK_a,COOH} \approx 2$ and $\mathrm{pK_a,NH_3^+} \approx 9.5$?

Accepted Answer

-1

Question 20

Which amino acid is most flexible due to its small size and lack of a chiral center?

Accepted Answer

Glycine

Protein Structure, Amino Acids, and pH: Foundations of Biochemistry

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