L4 Amino Acids and Proteins

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Question #1

The charge of glutamic acid at pH > 10 is

A +1

B -2

C +2

D 0

Question #2

The charge of cysteine at pH below 2 is

A -2

B 0

C +1

D -1

Question #3

The lowest charge possible for glutamic acid is

A -1

B -2

Question #4

What is the charge of the dipeptide Ala-Lys a pH = 12?

A +2

B +1

C -1

D 0

Question #5

At pH = 13, the net charge on lysine is:____________

A +1

B -1

C +3

D +2

Question #6

At pH = 0, the net charge on glutamic acid is:____________

A +2

B 0

C +1

D -1

Question #7

Based on the pKa values given in the attached table (see canvas tables), in there any amino acid among the ones in the list below that could serve as a buffer at pH 8.0?

A Histidine

B Leucine

C Glutamic acid

D Cysteine

E Tyrosine

Question #8

Which of the following amino acids has a net negative charge at physiologic pH (~7.4)?

A Asparagine

B Glutamic Acid

C Lysine

D Histidine

Question #9

The fully protonated form of histidine has a ____________charge.

A +4

B +3

C +2

D +1

Question #10

Chose the best true statement

A Proteases can cleave at specific points in the peptide chain

B Two of the statement are incorrect

C Cleave all peptide bonds

D Proteases are involved in many biological functions, including digestion of eaten proteins, and protein catabolism

E Proteases are involved in anabolism

Question #11

Proteases

A Cleave peptide bonds

B Degrade proteins

C three of the choices are correct

D cleaves disulfide bonds

E Produce amino acids or short peptides

Question #12

A protease

A increases the rate of proteolysis

B is also called a peptidase or proteinase

C cleaves proteins by the addition of a molecule of water to a peptide bond

D All the above statements are correct

E is an enzyme that catalyzes proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids

Question #13

Which of the following is an amino acid?

A Alanine

B Proline

C Glycine

D Serine

Question #14

Of the 20 standard amino acids, only ___________ is not optically active (nonchiral). The reason is that its side chain ___________.

A glycine; is unbranched

B proline; forms a covalent bond with the amino group

C alanine; is a simple methyl group

D lysine; contains only nitrogen

E glycine; is a hydrogen atom

Question #15

How many different standard amino acids are there?

A an infinite number

B 20

C 100

D 3

Question #16

Which of the following pairs of amino acids would carry a negative charge on their side chain at pH 8.0?

A Aspartate & Glutamate

B Asparagine & Glutamine

C Histidine & Lysine

D Leucine & Glycine

Question #17

An essential amino acid is one that

A the body cannot synthesize

B is essentially easy to synthesize

C the body can synthesize under essential conditions

D is essential to flagella motion

Question #18

Which one of the following amino acids contains an aromatic group?

A Leucine

B Phenylalanine

C Arginine

D Glycine

E Methionine

Question #19

A prosthetic group is:

A a subunit of an oligomeric protein

B synonymous with “protomer”

C a fibrous region of a globular protein

D a nonidentical subunit of a protein with many identical subunits

E a part of the protein that is not composed of amino acids

Question #20

At the isoelectric pH of a tetrapeptide:

A there are four ionic charges

B two internal amino acids of the tetrapeptide cannot have ionizable R groups

C the amino and carboxyl termini are not charged

D only the amino and carboxyl termini contribute charge

E the total net charge is zero

Question #21

The formation of a peptide bond between two amino acids is an example of a(n) ______________ reaction.

A oxidation reduction

B condensation

C group transfer

D cleavage

E isomerization

Question #22

For amino acids with neutral R groups, at any pH below the pI of the amino acid, the population of amino acids in solution will have:

A positive and negative charges in equal concentration

B no charged groups

C no net charge

D a net negative charge

E a net positive charge

Question #23

Titration of valine by a strong base, for example NaOH, reveals two pK’s. The titration reaction occurring at pK2 (pK2 = 9.62) is:

A —COOH + —NH2 → —COO– + —NH2+

B —COO– + —NH2+ → —COOH + —NH2

C —NH2 + OH– → —NH– + H2O

D —COOH + OH– → —COO– + H2O

E —NH3+ + OH– → —NH2 + H2O

Question #24

Amino acids are ampholytes because they can function as either a(n):

A acid or a base

B polar or a nonpolar molecule

C neutral molecule or an ion

D standard or a nonstandard monomer in proteins

E transparent or a light-absorbing compound

Question #25

The chirality of an amino acid results from the fact that its α carbon:

A has no net charge

B is bonded to four different chemical groups

C is symmetric

D is in the L absolute configuration in naturally occurring proteins

E is a carboxylic acid

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L4 Amino Acids and Proteins

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