Question 1

Matching

-In the tripeptide Lys─Pro─Ile,the C-terminal residue is _________.

Accepted Answer

The C-terminal residue in the tripeptide Lys─Pro─Ile is Isoleucine (abbreviated as I or Ile). It is the last amino acid in the peptide chain and is located at the C-terminus.

Question 2

Which of the following statements is true?

Accepted Answer

Purines and pyrimidines, which are the building blocks of nucleic acids, can be synthesized from amino acids, among other precursors.

Question 3

About half of the 20 amino acids are called essential because

Accepted Answer

Essential amino acids are those that our bodies are unable to synthesize and therefore need to be obtained from our diet. These amino acids are necessary for the production of proteins and other important biomolecules in our bodies.

Question 4

Matching

-Glutathione is a tripeptide containing a central ______ residue.

Accepted Answer

Glutathione contains a central cysteine residue, which is essential for its antioxidant activity.

Question 5

Matching

-Biological systems usually produce a single enantiomer,whereas chemical synthesis produces a ______.

Accepted Answer

Chemical synthesis typically produces a racemic mixture, which contains equal amounts of both enantiomers.

Question 6

Matching

-In the tripeptide Lys─Pro─Ile,there are ______ charged groups at pH 7.

Accepted Answer

At pH 7, the tripeptide Lys─Pro─Ile has three charged groups: the N-terminus (protonated amino group), the C-terminus (deprotonated carboxyl group), and the side chain of lysine (protonated amino group).

Question 7

Which of the following amino acids is the least abundant in proteins?

Accepted Answer

Tryptophan (W) is the least abundant amino acid in proteins, comprising only about 1% of the amino acid residues in proteins.

Question 8

Matching

-GABA is a neurotransmitter derived from ______.

Accepted Answer

GABA is derived from glutamate via the enzyme glutamate decarboxylase.

Answer: E
 GABA contains an amino group (-NH2) which is derived from the amino acid precursor glutamate.

Answer: L
 GABA can exist in either a protonated (positively charged) or deprotonated (uncharged) form depending on the pH of the surrounding environment. The protonated form is the active form of GABA in the brain.

Answer: P
 GABA is synthesized from glutamate in a process that begins at the N-terminus of the glutamate molecule.

Question 9

Which amino acid does not have a primary $\alpha$-amino group?

Accepted Answer

Proline does not have a primary F1F1F1S1F1F1F10-amino group as its amino group is shared as a part of the cyclic structure. The other amino acids listed (glutamine, arginine, lysine, and glutamate) have primary amino groups in their structure.

Question 10

The formation of a dipeptide from two amino acids involves

Accepted Answer

The formation of a dipeptide from two amino acids involves the removal of a water molecule, which is known as a dehydration or condensation reaction. This results in the formation of a peptide bond between the carboxyl group of one amino acid and the amino group of the other amino acid. The other options (A, C, D, E) are not involved in this process.

Question 11

Matching -At a pH below its pK_a,the $\beta$-carboxylate group of Asp is ______.

Accepted Answer

The answer of Matching -At a pH below its pK_a,the $\beta$-carboxylate...

Question 12

Zwitterions are

Accepted Answer

Zwitterions are ions that contain both positive and negative charges but are overall electrically neutral. This is characteristic of many amino acids at physiological pH, where the amino group is protonated (positive charge) and the carboxyl group is deprotonated (negative charge).

Question 13

Matching

-When a peptide bond is formed,an ______ reacts with a carboxylate group.

Accepted Answer

When a peptide bond is formed, an amino group reacts with a carboxylate group.

Answer: G
 The C-terminus of one amino acid reacts with the N-terminus of another amino acid during peptide bond formation.

Question 14

Matching

-In the peptide Trp─Ser─Val,valine is at the ______.

Accepted Answer

Valine is the last amino acid in the peptide sequence Trp─Ser─Val, making it the C-terminus.

Question 15

Matching -At a pH above its pK_a,the phenol group of tyrosine is ______.

Accepted Answer

Deprotonated means that the hydrogen ion dissociates from the phenol group, resulting in a negatively charged tyrosine molecule.

Answer: B
 If the phenol group of tyrosine is not deprotonated, it will remain in its neutral form and will not have a charge.

Answer: L
 If the phenol group of tyrosine is protonated, it will have an extra hydrogen ion attached to it, resulting in a positively charged tyrosine molecule.

Question 16

Matching -At a pH below its pK_a,the $\varepsilon$-amino group of lysine is ______.

Accepted Answer

At a pH below its pKa, the amino group of lysine is protonated, meaning it carries an extra hydrogen ion, making it positively charged rather than uncharged.

Question 17

What percentage of the 20 amino acids is considered to be nutritionally essential to lab animals?

Accepted Answer

Out of the 20 amino acids, lab animals are typically unable to synthesize 50% of them and must obtain them through their diet. These amino acids are considered nutritionally essential.

Question 18

Matching

-In the tripeptide Trp─Val─Phe,the N-terminal residue is ______.

Accepted Answer

EThe N-terminal residue of the tripeptide Trp─Val─Phe is tryptophan (N), and the N-terminal end of a peptide is characterized by a free amino group (E).

Question 19

In the early 1930's William Rose fed laboratory rats a mixture of all 19 amino acids known to be present in proteins.He observed that his rats lost weight.This observation led to the discovery of ______ as the 20th amino acid found in proteins.

Accepted Answer

Threonine (Thr) was discovered as the 20th amino acid found in proteins due to the observation that rats lost weight when fed a diet lacking this essential amino acid, highlighting its necessity for proper nutrition and growth.

Question 20

Matching

-The net charge of the zwitterion form of Gly is ______.

Accepted Answer

The zwitterion form of amino acids exists at a pH where the amino group (-NH2) is protonated (+NH3) and the carboxyl group (-COOH) is deprotonated (-COO-). This results in an overall net charge of 0, making the answer K the correct choice.

Quiz 4: Amino Acids

Matching -In the tripeptide Lys─Pro─Ile,the C-terminal residue is _________.

Which of the following statements is true?

About half of the 20 amino acids are called essential because

Matching -Glutathione is a tripeptide containing a central ______ residue.

Matching -Biological systems usually produce a single enantiomer,whereas chemical synthesis produces a ______.

Matching -In the tripeptide Lys─Pro─Ile,there are ______ charged groups at pH 7.

Which of the following amino acids is the least abundant in proteins?

Matching -GABA is a neurotransmitter derived from ______.

Which amino acid does not have a primary $\alpha$ -amino group?

The formation of a dipeptide from two amino acids involves

Matching -At a pH below its pK_a,the $\beta$ -carboxylate group of Asp is ______.

Zwitterions are

Matching -When a peptide bond is formed,an ______ reacts with a carboxylate group.

Matching -In the peptide Trp─Ser─Val,valine is at the ______.

Matching -At a pH above its pK_a,the phenol group of tyrosine is ______.

Matching -At a pH below its pK_a,the $\varepsilon$ -amino group of lysine is ______.

What percentage of the 20 amino acids is considered to be nutritionally essential to lab animals?

Matching -In the tripeptide Trp─Val─Phe,the N-terminal residue is ______.

In the early 1930's William Rose fed laboratory rats a mixture of all 19 amino acids known to be present in proteins.He observed that his rats lost weight.This observation led to the discovery of ______ as the 20th amino acid found in proteins.

Matching -The net charge of the zwitterion form of Gly is ______.

Quiz 4: Amino Acids

Matching -In the tripeptide Lys─Pro─Ile,the C-terminal residue is _________.

Which of the following statements is true?

About half of the 20 amino acids are called essential because

Matching -Glutathione is a tripeptide containing a central ______ residue.

Matching -Biological systems usually produce a single enantiomer,whereas chemical synthesis produces a ______.

Matching -In the tripeptide Lys─Pro─Ile,there are ______ charged groups at pH 7.

Which of the following amino acids is the least abundant in proteins?

Matching -GABA is a neurotransmitter derived from ______.

Which amino acid does not have a primary α\alphaα -amino group?

The formation of a dipeptide from two amino acids involves

Matching -At a pH below its pKa,the β\betaβ -carboxylate group of Asp is ______.

Zwitterions are

Matching -When a peptide bond is formed,an ______ reacts with a carboxylate group.

Matching -In the peptide Trp─Ser─Val,valine is at the ______.

Matching -At a pH above its pKa,the phenol group of tyrosine is ______.

Matching -At a pH below its pKa,the ε\varepsilonε -amino group of lysine is ______.

What percentage of the 20 amino acids is considered to be nutritionally essential to lab animals?

Matching -In the tripeptide Trp─Val─Phe,the N-terminal residue is ______.

In the early 1930's William Rose fed laboratory rats a mixture of all 19 amino acids known to be present in proteins.He observed that his rats lost weight.This observation led to the discovery of ______ as the 20th amino acid found in proteins.

Matching -The net charge of the zwitterion form of Gly is ______.

Which amino acid does not have a primary $\alpha$ -amino group?

Matching -At a pH below its pK_a,the $\beta$ -carboxylate group of Asp is ______.

Matching -At a pH above its pK_a,the phenol group of tyrosine is ______.

Matching -At a pH below its pK_a,the $\varepsilon$ -amino group of lysine is ______.