Chapter 3 (Amino Acids)

The charge of glycine when the pH is < 2.0 is __________.

+1

Draw the general structure of an amino acid at pH 7.0 with the side group shown as an "R."

+H3N and COO-

Which of the following amino acids would most likely be soluble in a nonpolar solvent such as benzene? A) valine B) histidine C) glutamine D) glycine E) All of the above.

A

Which amino acids have a side chain that includes a modified carboxyl group, carboxaminde?

Asparagine and glutamine

At a pH of 12, what charged group(s) is/are present in glycine? A) -NH3+ B) -COO− C) -NH2+ D) A and B E) A, B, and C

B

Interactions between side chains of and Aspartate and Arginine at neutral pH would be? A) hydrophobic B) ionic C) hydrogen bonding D) steric E) covalent

B

Which amino acids contain reactive aliphatic hydroxyl groups? A) serine and methionine B) serine and threonine C) methionine and threonine D) cysteine and methionine E) cysteine and threonine

B

What are the three aromatic amino acids?

Phenylalanine, tyrosine, and tryptophan

Draw the structure of alanine, aspartic acid, and histidine when the pH is 1.0, 7.0, and 12.0.

Use the figures in your book and the pKa for each functional group to determine the ionization state for each amino acid.

Draw a titration curve for glycine.

Use the information from Chapter2 , Section 2.5 and the graph from Figure 3.2.

What is the advantage of protein interaction and assembly with other proteins?

When proteins interact or assemble, new functions and specificity become available. These protein interactions provide multifunctional activity and specificity.

____________:The amino acid with whose side group has a terminal carboxamide.

asparagine

Between the amino and the carboxyl functional group, the ________ has the lowest affinity for a proton.

carboxyl

____________: Disulfide bonds are formed by pairs of this amino acid.

cysteine

____________: The amino acid with a sulfhydryl side chain.

cysteine

__________ is an amino acid with a hydrophobic side chain containing a thioether.

methionine

The group of amino acids that can be supplied by an organism under a defined condition are the ______ amino acids.

nonessential

__________ are amino acids with neutral R groups containing an electronegative atom that hoards electrons.

polar amino acids

____________: The amino acid with the abbreviation Ser.

serine

The amino acid with an indol ring is __________.

tryptophan

The amino acid that contains a weakly acidic "phenolic" group is __________.

tyrosine

____________: Another name for dipolar molecules.

zwitterions

Name three amino acids that are positively charged at a neutral pH. A) lysine and arginine B) histidine and arginine C) cysteine and arginine D) lysine and proline E) glutamine and histidine

A

Which amino acid has a side chain with a hydroxyl group? A) serine B) alanine C) tryptophan D) histidine E) glutamine

A

Which amino acid is responsible for stabilizing the stucture of a protein by forming pairs of sulfhydryl groups?

Cysteine

What charged group(s) is/are present in glycine at a pH of 7? A) -NH3+ B) -COO− C) -NH2+ D) A and B E) A, B, and C

D

Which amino acid has a carboxyl group in its side chain? A) glutamine B) galanine C) cysteine D) glutamate E) None of the above.

D

In what pH range is zwitterionic alanine the predominate structure? A) 0-2 B) 9-14 C) 8-10 D) 2-4 E) 2-9

E

The overall charge of a peptide of the following peptide sequence at pH 1 would be (Asp-Gly- Arg-His): A) −1 B) 0 C) 1 D) 2 E) 3

E

Serine, threonine and tyrosine all have what in common?

Each has a hydroxyl (-OH) group, which makes the first two amino acids more water soluble and increases the reactivity of all three amino acids.

____________ is often seen in a child with a protein-deficient diet.

Edema

What is the net charge of each amino acid for each of the cases in the question above?

For glycine, the charges are: 1, 0, and −1. For aspartic acid, the charges are: 1, −1, and −2. For histidine, the charges are: 2, 0, and −1.

List the essential amino acids.

Histadine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine

What are the four ways amino acids can be classified?

Hydrophobic, polar, positively charged, and negatively charged

____________: Chiral type of amino acids found in proteins.

L amino acids

Which amino acid side chains are capable of ionization?

The amino acids are aspartate, glutamate, histidine, cylteine, tyrosine, lysine, and arginine.

What is the difference between nonessential and essential amino acids?

The former are amino acids that humans can generate de novo, or from scratch. The latter cannot be made and must be ingested for the mature formation of proteins.

A gene is mutated such that the amino acids glycine and glutamate are now alanine and leucine, respectively.What are the potential results of each of these mutations? Assume that the mutations are not near each other in the primary sequence and have no impact on the other.

The glycine-to-alanine mutations are similar and will have little or no effect. Glutamate and leucine have very different chemistries and will impact the function and structure of the protein, as one is charged and water soluble and the other is hydrophobic and nonpolar.

What functions make histadine an important amino acid?

The pKa of the imidazole ring is near physiolical pH.This means that the side group may be charged and protonized or neutral and deprotonated. This results in an amino acid which can either lend or accept a proton or charge in the active site of an enzyme.

What is the advantage of having multiple functional groups in proteins?

The rich diversity of functional groups in proteins can independently contribute to protein structure and accounts for the diversity in function as well.

Which ionizable group has the lowest affinity for protons: the terminal α-carboxyl group, the aspartic acid side group, or the terminal α-amino group?

The terminal α-carboxyl group

Which are the branched amino acids and what impact do they have on protein shape?

These are the aliphatic, hydrophobic amino acids, valine, leucine and isoleucine.They are hydrophobic, which drives the hydrophobic interactions in the interior of a protein. These are also bulky amino acids that will lend to steric strain if forced close to each other in a peptide.

Even though malnourished, children with Kwashiorkor display a distended stomach, giving the illusion of being full. Why does this happen?

This is a nutritional state where there is an extremely low or poor protein intake in the diet. The osmolar shift of the blood, which is poor in protein content, causes water to flow into the tissues.

Why is the central carbon on an amino acid so important?

This is the chiral center of the molecule and is linked to each important functional group of an amino acid.

____________: The amino acid with a negatively charged side chain at neutral pH.

glutamate

The amino acid with the smallest-size side chain allowing greatest flexibility in a protein is __________.

glycine

____________: An amino acid that must be supplied by the diet.

histidine

____________: The amino acid with a pKa near neutral pH.

histidine

____________: The amino acid with an imidazole side chain.

histidine

The ____________ group is the functional group that makes an amino acid more reactive than nonpolar amino acids such as valine, alanine, and phenylalanine.

hydroxyl