Question 1

The pK₁,pK₂,and pK_R for the amino acid glutamate are 2.1,9.5,and 4.1,respectively.At pH 11.0,glutamate would be charged predominantly as follows:

Accepted Answer

At pH 11.0, both the α-carboxylate and γ-carboxylate groups of glutamate would be deprotonated (charged as -1) due to their pKa values being lower than the pH (2.1 and 4.1, respectively). The α-amino group, with a pKa of 9.5, would be protonated (neutral, 0 charge) because the pH is higher than its pKa. Thus, the net charge would be -2.

Question 2

The ionization of amino acids depends on the pH and the pK_as of the ionizable groups.The pK₁ and pK₂for the amino acid shown above are 2.1 and 8.8,respectively.At what pH is the amino acid ionized predominantly as shown?

Accepted Answer

The answer of The ionization of amino acids depends on...

Question 3

The pK₁,pK₂,and pK_R for the amino acid aspartic acid are 2.0,9.9,and 3.9,respectively.At pH 7.0,aspartic acid would be charged predominantly as follows:

Accepted Answer

The pH is close to the pKa of the carboxyl group (pK₁ = 2.0) and the pKa of the amino group (pK₂ = 9.9). At pH 7.0, the carboxyl group will be deprotonated (−1 charge) and the amino group will be protonated (+1 charge), resulting in a net charge of −1.

Question 4

Which of the following amino acids has an uncharged polar side chain at pH 7.0?

Accepted Answer

Threonine (Thr) has an uncharged polar side chain at pH 7.0 due to the presence of a hydroxyl (-OH) group. Arginine (Arg) and Glutamic acid (Glu) have charged side chains, Proline (Pro) has a nonpolar side chain, and Isoleucine (Ile) has a nonpolar, aliphatic side chain.

Question 5

Which of the following amino acids does not have an ionizable side chain?

Accepted Answer

Asn (Asparagine) does not have an ionizable side chain. It has an amide group in its side chain, which does not ionize under physiological conditions.

Question 6

Questions are based on the diagram shown below. 
-What is the three-letter symbol for the C-terminal amino acid in the peptide shown above?

Accepted Answer

The answer of Questions are based on the diagram shown...

Question 7

Which of the following amino acids has a charged polar side chain at pH 7.0?

Accepted Answer

Glutamic acid (Glu) has a negatively charged carboxylate group in its side chain at pH 7.0, making it a charged polar amino acid.

Question 8

Which of the following amino acids has a sulfur atom in its side chain?

Accepted Answer

The only amino acid with a sulfur atom in its side chain is methionine (Met).

Question 9

The two peptides shown in the diagram below are linked through

Accepted Answer

The answer of The two peptides shown in the diagram...

Question 10

Questions are based on the diagram shown below. 
-How many amino acid residues are present in the peptide shown above?

Accepted Answer

The peptide shown above contains three amino acid residues, as indicated by the presence of three distinct amino acid units linked by peptide bonds.

Question 11

The pK₁,pK₂,and pK_R for the amino acid lysine are 2.2,9.1,and 10.5,respectively.At pH 1.0,lysine would be charged predominantly as follows:

Accepted Answer

At low pH (pH 1.0), the lysine molecule will behave as a basic amino acid and lose a proton from its amino group to become positively charged. The carboxylate group will still be negatively charged, thus giving a net charge of +2 to the lysine molecule. Therefore, the correct choice is D. Choice A, B, C and E are incorrect as they show a net charge that is either too negative or too positive for a basic amino acid at low pH.

Question 12

For the following questions  refer to the diagram below 
-What is the three-letter symbol for the amino acid shown above?

Accepted Answer

Asn is the three-letter symbol for the amino acid asparagine.

Question 13

The diagram below shows

Accepted Answer

The answer of The diagram below shows 
...

Question 14

The disulfide bond between two cysteine molecules

Accepted Answer

The disulfide bond between two cysteine molecules is a covalent bond formed by oxidation.

Question 15

The pK₁,pK₂,and pK_R for the amino acid histidine are 1.8,9.3,and 6.0,respectively.At pH 4.0 would be charged predominantly as follows:

Accepted Answer

The answer of The pK₁,pK₂,and pK_R for the amino acid...

Question 16

The pK₁,pK₂,and pK_R for the amino acid arginine are 1.8,9.0,and 12.5,respectively.At pH 7.0 arginine would be charged predominantly as follows:

Accepted Answer

At pH 7.0, the carboxylate group (pKa = 1.8) would be deprotonated and negatively charged, the amino group (pKa = 9.0) would be protonated and positively charged, and the guanidino group (pKa = 12.5) would also be protonated and positively charged, resulting in a net charge of +1 for arginine.

Question 17

While proteins are usually composed of linear chains of amino acids,branched chains of amino acids and internally cross-linked chains can be found in certain proteins.Polypeptide chains are most commonly linked to each other through

Accepted Answer

Disulfide bonds are covalent bonds that commonly link polypeptide chains together, especially in proteins with multiple subunits or in the stabilization of protein tertiary and quaternary structures.

Question 18

Questions are based on the diagram shown below. 
-What is the name of the N-terminal amino acid in the peptide shown above?

Accepted Answer

The first amino acid in a peptide is typically a methionine. This is due to the initiation codon AUG, which codes for methionine, being the typical start codon for protein synthesis in eukaryotes.

Question 19

Which of the following tripeptides carries a net positive charge at pH 7.0?

Accepted Answer

At pH 7.0, the net charge of a peptide is determined by the ionizable side chains of the amino acids it contains. In option E, Leu─Lys─Gly, Lysine (Lys) has a positively charged side chain at pH 7.0, while Leucine (Leu) and Glycine (Gly) have neutral side chains. Therefore, this tripeptide carries a net positive charge.

Question 20

The pK₁,pK₂,and pK_R for the amino acid cysteine are 1.9,10.7,and 8.4,respectively.At pH 5.0,cysteine would be charged predominantly as follows:

Accepted Answer

At pH 5.0, the carboxyl group (pKa = 1.9) would be deprotonated and carry a negative charge. The amino group (pKa = 10.7) would be protonated and carry a positive charge. The sulfhydryl group (pKa = 8.4) is not acidic enough to lose a proton at pH 5.0, so it remains neutral. This results in a net charge of 0 for cysteine at pH 5.0.

Quiz 4: Amino Acids

The pK1,pK2,and pKR for the amino acid glutamate are 2.1,9.5,and 4.1,respectively.At pH 11.0,glutamate would be charged predominantly as follows:

The ionization of amino acids depends on the pH and the pKas of the ionizable groups.The pK1 and pK2 for the amino acid shown above are 2.1 and 8.8,respectively.At what pH is the amino acid ionized predominantly as shown?

The pK1,pK2,and pKR for the amino acid aspartic acid are 2.0,9.9,and 3.9,respectively.At pH 7.0,aspartic acid would be charged predominantly as follows:

Which of the following amino acids has an uncharged polar side chain at pH 7.0?

Which of the following amino acids does not have an ionizable side chain?

Questions are based on the diagram shown below. -What is the three-letter symbol for the C-terminal amino acid in the peptide shown above?

Which of the following amino acids has a charged polar side chain at pH 7.0?

Which of the following amino acids has a sulfur atom in its side chain?

The two peptides shown in the diagram below are linked through

Questions are based on the diagram shown below. -How many amino acid residues are present in the peptide shown above?

The pK1,pK2,and pKR for the amino acid lysine are 2.2,9.1,and 10.5,respectively.At pH 1.0,lysine would be charged predominantly as follows:

For the following questions refer to the diagram below -What is the three-letter symbol for the amino acid shown above?