Amino Acids (MC)

Electrophoretic separation of Leucine from a protein sample would be least effective at which of the following pH values? A. 7.4 B. 2.4 C. 1.4 D. 0.4

A. 7.4

The side chains of which of the following amino acids could participate in a salt bridge bonding interaction? A. Aspartic acid B. Phenylalanine C. Cysteine D. Serine

A. Aspartic acid Explanation: salt brides are between the side chains of an acidic and a basic amino acid residue (a negative/positive interaction). The only acidic amino acid is aspartic acid that could participate

The side groups of which amino acids can mimic a permanently phosphorylated amino acid? A. Aspartic acid and Glutamic acid B. Histidine and Lysine C. Threonine and Serine D. Glutamine and Arginine

A. Aspartic acid and Glutamic acid Explanation: Both side chains are bulky and negatively charged which can mimic a phosphate in certain settings.

Which amino acid has a net negative charge at physiologic pH (~7.4)? A. Glutamic Acid B. Histidine C. Lysine D. Asparagine

A. Glutamic Acid

Amino acids in hemoglobin (or any protein) uniformly have which of the following configuration? A. L configuration B. R configuration C. S configuration D. D configuration

A. L configuration

All hydrophobic amino acids (valine, leucine, isoleucine, etc.) share which of the following properties? A. Nonpolar uncharged R groups B. Polar uncharged R groups C. Basic R groups D. Acidic R groups

A. Nonpolar uncharged R groups

The unique cyclic structure of which of the following amino acids plays a central role in the formation of alpha helices and beta sheets? A. Proline B. Arginine C. Valine D. Lysine

A. Proline

The alpha helix is an example of which of the following structural properties of proteins? A. Secondary structure B. Quaternary structure C. Primary structure D. Tertiary structure

A. Secondary structure

Which of the following does NOT make up the side group ("R" group) of one of the 20 amino acids? A. Thioester B. Thiol C. Methyl D. Hydroxyl

A. Thioester Explanation: the wording is what trips you up. Thioester - though it makes up part of a side group, it does not make up the ENTIRE side group and that's what they're asking.

Which of the following properties of a protein is LEAST likely to be affected by changes in pH? A. Tertiary structure B. Primary structure C. Secondary structure D. Net charge

B. Primary structure

Which of the following amino acids contains a positively charged side chain at a physiological pH (~7.4)? A. Glutamic acid B. Serine C. Arginine D. Glycine

C. Arginine Explanation: positively charged amino acids have protonated amino groups, the positively charged amino acids are arginine, lysine, and sometimes histidine

L-amino acids all have S configurations except for which amino acid? A. Methionine B. Valine C. Cystenine D. Tryptophan

C. Cystenine Explanation: Cystenine has R chirality because of the sulfur which has a heavier molecular weight in its R group.

Which of the following amino acids is NOT a nonpolar amino acid? A. Tryptophan B. Methionine C. Threonine D. Proline

C. Threonine Explanation: Threonine contains a hydroxyl in it's side chain which makes it polar

The side groups of which amino acids are common targets for phosphorylation in biological settings? A. Histidine, Lysine, Arginine B. Phenylalanine, Tyrosine, Tryptophan C. Tyrosine, Serine, Threonine D. Glutamine and Arginine

C. Tyrosine, Serine, Threonine Explanation: the three side groups most often the targets of phosphorylation are tyrosine, serine, and threonine. phosphorylation is the addition of a negatively charged phosphate to a molecule which often changes the structure or function of that molecule. *note each of these three amino acids features a hydroxyl function

Hydrogen bonding between separate subunits of DNA polymerase is an example of which of the following? A. 1st degree structure B. 2nd degree structure C. 3rd degree structure D. 4th degree structure

D. 4th degree structure

A polypeptide with a net positive charge at physiologic pH (~7.4) most likely contains amino acids with R groups of what type? A. Acidic R groups B. Aromatic R groups C. Aliphatic R groups D. Basic R groups

D. Basic R groups

Which of the following amino acids is not optically active? A. Leucine B. Isoleucine C. Valine D. Glycine

D. Glycine Explanation: most amino acids have chiral centers located at their alpha carbon - because of the 4 different substituents attached to the R group. The chiral center makes them optically active. Glycine has a single hydrogen atom as its R group and 2 hydrogens bonded to it's alpha carbon. It cannot have a chiral center therefore it is optically inactive.

Electrophoretic separation of pH of 6 of a sample of polypeptide 1 (mw100), polypeptide 2 (mw200), and polypeptide 3 (mw300) would result in which of the following? A. Polypeptide 1 would move the farthest B. Polypeptide 2 would move the farthest C. Polypeptide 3 would move the farthest D. None of the polypeptides would move

D. None of the polypeptides would move

Which of the following amino acids does NOT contain an aromatic ring? A. Histidine B. Phenylalanine C. Tyrosine D. Proline

D. Proline Explaination: Proline contains a ring that is NOT aromatic. There are 4 amino acids whose side groups contain aromatic rings: histidine, tyrosine, phenylalanine, and tryptophan.

Which amino acids are generally NOT present within the structure of alpha helices? A. Proline and Phenylalanine B. Phenylalanine and Tryptophan C. Aspartic acid and Glutamic acid D. Proline and Glycine

D. Proline and Glycine Explanation: if proline or glycine were to be added to a protein it would often times break down the protein or destabilize the structure