Question 1

Which of the following statements best describes the difference between L- and D-amino acids in biological systems?

Accepted Answer

L-amino acids are generally incorporated into proteins in living organisms, whereas D-amino acids are rare and mainly found in bacterial cell walls and some specialized structures.

Question 2

Amino acids are classified as amphoteric compounds. What does this mean?

Accepted Answer

They can act as both acids and bases, reacting with both to form salts.

Question 3

Which of the following amino acids is essential and must be obtained from the diet?

Accepted Answer

Leucine

Question 4

At physiological pH ($pH \approx 7.4$), which form do most amino acids exist in?

Accepted Answer

As zwitterions, with both a positively charged amino group and a negatively charged carboxyl group

Question 5

Which equation correctly calculates the isoelectric point ($pI$) of glycine, given $pK_1 = 2.34$ and $pK_2 = 9.60$?

Accepted Answer

$pI = (2.34 + 9.60)/2$

Question 6

A patient’s blood sample shows a high concentration of modified amino acids such as hydroxyproline and hydroxylysine. Which tissue is most likely being degraded?

Accepted Answer

Collagen-rich connective tissue

Question 7

Which of the following amino acids contains a secondary amino group instead of a primary $	ext{α}$-amino group?

Accepted Answer

Proline

Question 8

Which chemical bond is responsible for the primary structure of proteins?

Accepted Answer

Peptide bond

Question 9

During the titration of glutamic acid, three distinct $pK$ values are observed. Which group is responsible for the third $pK$ value?

Accepted Answer

The side chain carboxyl group

Question 10

Which of the following amino acids is most likely to be found on the interior of a globular protein due to its hydrophobic nature?

Accepted Answer

Valine

Question 11

Which of the following bonds or interactions remains intact after complete denaturation of a protein by heat and pH?

Accepted Answer

Disulfide bonds

Question 12

Which amino acid can form hydrogen bonds through its side chain, contributing to the stabilization of tertiary protein structure?

Accepted Answer

Asparagine

Question 13

Which of the following is a real-life application of ion-exchange chromatography in biochemistry?

Accepted Answer

Purifying amino acids from a protein hydrolysate

Question 14

A polypeptide chain is treated with trypsin. Which amino acid residues will be cleaved?

Accepted Answer

Lysine and Arginine

Question 15

Which of the following amino acids is aromatic and can absorb UV light, making it useful in protein quantification assays?

Accepted Answer

Tryptophan

Question 16

Which chemical reaction is responsible for the conversion of glutamate to gamma-aminobutyric acid (GABA) in the brain?

Accepted Answer

Decarboxylation

Question 17

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

Accepted Answer

It is stabilized mainly by hydrogen bonds between backbone atoms.

Question 18

A protein is found to have four subunits, each with its own tertiary structure. What level of protein structure does this represent?

Accepted Answer

Quaternary structure

Question 19

Which of the following amino acids is most likely to form a blue complex with Ninhydrin reagent?

Accepted Answer

Glycine

Question 20

Which post-translational modification is important for the regulation of protein activity and can be reversed by specific enzymes?

Accepted Answer

Phosphorylation

Amino Acids and Proteins: Structure, Properties, and Classification

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