Question 1

Which of the following best explains the molecular basis of sickle cell anemia?

Accepted Answer

A single amino acid substitution from glutamic acid to valine in the beta chain of hemoglobin

Question 2

At physiological pH ($$\approx 7.4$$), what is the predominant ionization state of a generic $$b-$$amino acid?

Accepted Answer

The amino group is protonated ($$\mathrm{NH_3$^+}) $$and the carboxyl group is deprotonated ($$\mathrm{COO^-}$$), forming a zwitterion

Question 3

Which amino acid is NOT chiral and why?

Accepted Answer

Glycine, because its side chain is a hydrogen atom

Question 4

Which property of aromatic amino acids allows proteins to be quantified by UV absorbance at 280 nm?

Accepted Answer

Their aromatic rings absorb strongly in the near-ultraviolet region

Question 5

Which of the following amino acids contains a thiol ($$\mathrm{-SH}) $$group and can form disulfide bonds?

Accepted Answer

Cysteine

Question 6

A protein is found to have a net charge of zero at pH 6.0. What is this pH called for the protein?

Accepted Answer

Isoelectric point ($$pI)$$

Question 7

Which post-translational modification introduces additional negative charges and is important for blood clotting proteins?

Accepted Answer

Carboxylation of glutamate

Question 8

Which amino acid side chain is most likely to be protonated at physiological pH, contributing to positive charge?

Accepted Answer

Lysine

Question 9

Which of the following best describes the process of protein synthesis in eukaryotic cells?

Accepted Answer

mRNA is transcribed from DNA in the nucleus, exported to the cytoplasm, and translated into a linear sequence of amino acids

Question 10

Which amino acid is most likely to be found in the active site of an enzyme due to its nucleophilic side chain?

Accepted Answer

Serine

Question 11

Which of the following amino acids is classified as aromatic?

Accepted Answer

Tyrosine

Question 12

What is the main difference between L- and D- amino acids in proteins?

Accepted Answer

L-amino acids are found in proteins, while D-amino acids are not

Question 13

Which amino acid is most likely to be involved in hydrogen bonding due to its polar side chain?

Accepted Answer

Threonine

Question 14

A mutation changes a codon from coding for glutamic acid to valine. What is the likely effect on protein structure?

Accepted Answer

Disruption of protein folding due to replacement of a charged side chain with a nonpolar one

Question 15

Which amino acid has a side chain with a guanidinium group and is highly basic?

Accepted Answer

Arginine

Question 16

Which of the following is a correct representation of the peptide bond formation between two amino acids?

Accepted Answer

$$\mathrm{R_1$-CH(NH_2$)-COOH + R_2$-CH(NH_2$)-COOH \rightarrow R_1$-CH(NH_2$)-CO-NH-CH(R_2$)-COOH + H_2O}$$

Question 17

Which amino acid is most likely to be phosphorylated during cell signaling?

Accepted Answer

Serine

Question 18

Which of the following amino acids has a side chain that can act as a buffer near physiological pH due to its $$pK_a$$?

Accepted Answer

Histidine

Question 19

Which amino acid is most likely to be found in collagen due to its ability to form strong hydrogen bonds after hydroxylation?

Accepted Answer

Proline

Question 20

Which of the following best describes the role of tau protein deposits in Alzheimer's disease?

Accepted Answer

Tau protein deposits are associated with neurodegeneration in Alzheimer's disease

Amino Acids and Proteins: Structure, Properties, and Biological Significance

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