L4 Amino Acids and Proteins

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Question #1

The charge of glutamic acid at pH > 10 is

A 0

B -2

C +2

D +1

Question #2

The charge of cysteine at pH below 2 is

A -2

B -1

C +1

D 0

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 0

B -1

C +2

D +1

Question #5

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

A +1

B +3

C -1

D +2

Question #6

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

A +1

B 0

C -1

D +2

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 Tyrosine

B Glutamic acid

C Cysteine

D Histidine

E Leucine

Question #8

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

A Histidine

B Glutamic Acid

C Asparagine

D Lysine

Question #9

The fully protonated form of histidine has a ____________charge.

A +2

B +3

C +4

D +1

Question #10

Chose the best true statement

A Cleave all peptide bonds

B Two of the statement are incorrect

C Proteases are involved in anabolism

D Proteases can cleave at specific points in the peptide chain

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

Question #11

Proteases

A Cleave peptide bonds

B Degrade proteins

C cleaves disulfide bonds

D Produce amino acids or short peptides

E three of the choices are correct

Question #12

A protease

A is also called a peptidase or proteinase

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

C increases the rate of proteolysis

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

E All the above statements are correct

Question #13

Which of the following is an amino acid?

A Glycine

B Proline

C Serine

D Alanine

Question #14

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

A lysine; contains only nitrogen

B alanine; is a simple methyl group

C glycine; is a hydrogen atom

D glycine; is unbranched

E proline; forms a covalent bond with the amino group

Question #15

How many different standard amino acids are there?

A 3

B an infinite number

C 100

D 20

Question #16

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

A Histidine & Lysine

B Asparagine & Glutamine

C Leucine & Glycine

D Aspartate & Glutamate

Question #17

An essential amino acid is one that

A is essential to flagella motion

B the body can synthesize under essential conditions

C the body cannot synthesize

D is essentially easy to synthesize

Question #18

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

A Phenylalanine

B Arginine

C Leucine

D Methionine

E Glycine

Question #19

A prosthetic group is:

A a subunit of an oligomeric protein

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

C a nonidentical subunit of a protein with many identical subunits

D a fibrous region of a globular protein

E synonymous with “protomer”

Question #20

At the isoelectric pH of a tetrapeptide:

A there are four ionic charges

B only the amino and carboxyl termini contribute charge

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

D the amino and carboxyl termini are not charged

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 condensation

B cleavage

C oxidation reduction

D group transfer

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 a net negative charge

B no net charge

C no charged groups

D a net positive charge

E positive and negative charges in equal concentration

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 —NH3+ + OH– → —NH2 + H2O

C —COOH + OH– → —COO– + H2O

D —NH2 + OH– → —NH– + H2O

E —COO– + —NH2+ → —COOH + —NH2

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 standard or a nonstandard monomer in proteins

D transparent or a light-absorbing compound

E neutral molecule or an ion

Question #25

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

A is a carboxylic acid

B is in the L absolute configuration in naturally occurring proteins

C has no net charge

D is symmetric

E is bonded to four different chemical groups

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L4 Amino Acids and Proteins

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