Biochemistry Exam 1

1-30 are quiz questions, the rest are things Dr. D stressed in class review

What is the net charge on the dipeptide lys-asp at a pH of 1.0?

A) +3

B) +1

C) +2

D) +4

C) +2, because in acidic conditions the amine gains H and the carboxyl stays neutral

How many of the 20 common amino acids contain acidic side chains?

A) 2

B) 1

C) 3

D) 0

A) 2, aspartic acid and glutamic acid

How many of the 20 common amino acids contain sulfur?

A) 1

B) 2

C) 3

D) 0

B) 2, methionine and cysteine

How many of the 20 common amino acids are achiral?
A) 0

B) 2

C) 3

D) 1

D) 1, glycine

The pKa’s of the -COOH groups of amino acids are usually between 2 and 3. Why are these so much lower than the pKa of acetic acid (4.7)

A) The amino group in amino acids can hydrogen bond with water.

B) The electron-withdrawing effect of the amino group increases the acidity of the acid group.

C) Amino acids are more soluble in water than acetic acid.

D) Amino acid are amphoteric

B) The electron-withdrawing effect of the amino group increases the acidity of the acid group. (NH3+ really positive)

How many of the 20 common amino acids are primary amines

A) 20

B) 18

C) 17

D) 19

D) 19, not proline

Which one of the following best defines the isoelectric point, pI?

A) The pH at which the charge on the amino acid is +1.

B) The pH at which the charge on the amino acid is 0.

C) The charge on the amino acid when the pH equals the pKa of the carboxylic acid group.

D) The charge on the amino acid when the pH is 7.0.

B) The pH at which the charge on the amino acid is 0

The amino groups in amino acids are

A) stronger bases than secondary amines.

B) same basicity of primary amines.

C) weaker bases than primary amines.

D) stronger bases than primary amines.

C) weaker bases than primary amines

Enantiomers are

A) Achiral

B) A pair of compounds that are not superimposable on their mirror images

C) Superimposable mirror images

D) Molecules with both hydrophobic and hydrophilic characteristics

B) A pair of compounds that are not superimposable on their mirror images

What is the name of the functional group at the end of the arginine side chain?

A) amidino group

B) imidazolium

C) guanidino group

D) amide

C) guanidino group

If the pI of amino acids with alkyl group side chains is 6.0, the pI of aspartic acid is ___________

A) larger than 6.0

B) equal to 6.0

C) less than 6.0

D) less than 0.0

C) less than 6.0

What is the relationship between the following two structures?

A) Diastereomers

B) Resonance forms

C) Keto-enol forms

D) Enantiomers

B) Resonance forms

Which one of the following amino acids has a side chain that is likely to be on the surface of a globular protein?

A) leucine

B) alanine

C) glutamic acid

D) phenylalanine

C) glutamic acid

Which of the following amino acids has its alpha carbon as part of a 5-membered ring?

A) proline

B) tryptophan

C) histidine

D) tyrosine

A) proline

What is the purpose of electrophoresis?

A) to neutralize amino acids

B) to synthesize amino acids or proteins

C) to separate amino acids or proteins

D) to analyze the amino acid sequence in a protein

C) to separate amino acids or proteins

What is the total number of tripeptides that can result from two L-alanines and one L-serine?

A) six

B) four

C) three

D) two

C) three, SAA, ASA, AAS

Nearly all naturally occurring amino acids _______?

A) have the (S) configuration at the alpha carbon.

B) have the (R) configuration at the alpha carbon.

C) are racemic mixtures.

D) have basic side chains.

A) have the (S) configuration at the alpha carbon.

Which of the following indicators is commonly used to visualize TLC bands of amino acids

A) Ninhydrin

B) Vanillin

C) potassium permanganate

D) bromocresol green

A) Ninhydrin

Which of the following arrangements is usually not found in the secondary structure of proteins

A) double helix

B) alpha helix

C) pleated sheet

D) random coil

A) double helix

Which amino acid has an imidazole ring in its side chain?

A) asparagine

B) tyrosine

C) tryptophan

D) histidine

D) histidine

Insulin is an example of a(an)

A) Storage protein

B) Transport protein

C) Hormone

D) Enzyme

C) Hormone

Myoglobin is a protein that contains oxygen in the muscles. To what class of protein does it belong?

A) Structural protein

B) Storage protein

C) Protective protein

D) Transport protein

B) Storage protein

All of the following are examples of fibrous proteins except.....

A) insulin

B) skin

C) wool

D) fingernails

A) insulin

All of the following are examples of denaturing proteins except.....

A) Souring of milk

B) Using a curling iron on your hair

C) Digestion of a cheeseburger

D) A mild sunburn

C) Digestion of a cheeseburger

Protein denaturation results in a disruption of the.....

A) Quaternary and Primary structure

B) Primary and Secondary structure

C) Secondary and Tertiary structure

D) Amino acid sequence

C) Secondary and Tertiary structure

Which protein is considered to be a globular protein?

A) collagen

B) albumin

C) keratin

D) myosin

B) albumin

The quaternary structure of hemoglobin contains......

A) 4 subunits

B) 2 subunits

C) 6 subunits

D) 8 subunits

 

A) 4 subunits

The protein configuration that is primarily the result of R group interactions is the…

A) tertiary structure

B) primary structure

C) secondary structure

D) quaternary structure

A) tertiary structure

All of the following are conjugated proteins except.....

A) hemoglobin

B) collagen

C) myoglobin

D) cytochrome P450

B) collagen

Proteins that consist of two or more chains assembled into a large 3-dimensional structure are said to display.....

A) secondary structure

B) primary structure

C) quaternary structure

D) tertiary structure

C) quaternary structure

What are the parts of an amino acid

carboxyl, amino, and side chain bonded to a C atom

Why are proteinogenic amino acids called alpha amino acids?

Because the amine group is on the alpha carbon

What determines the function of the amino acid in a protein

the side chain

How many proteinogenic amino acids are there

20

How many of the 20 amino acids are essential

10

What single amino acid has an R-configuration

cysteine

Are all amino acids L or R configurations

L

What are the neutral nonpolar aliphatic amino acids

Glycine, alanine, valine, leucine, isoleucine

What are the neutral nonpolar amino acids

proline, methionine

What are the neutral nonpolar aromatic amino acids

phenylalanine, tyrosine, tryptophan

What are the neutral polar amino acids

serine, cysteine, threonine, asparagine, glutamine

What are the basic amino acids

histidine, arginine, lysine

What are the acidic amino acids

glutamic acid, aspartic acid

Which two amino acids have two chiral centers

isoleucine and threonine

Which 2 amino acids have sulfur

methionine and cysteine

What does zwitterionic mean

the compound is overall neutral even though there are charged groups

Which amino acid is not chiral

glycine

In an integral protein where are nonpolar and polar amino acids located?

hydrophobic middle of the membrane and hydrophilic outside the membrane

Which amino acids serve as attachment and phosphorylation sites and why

serine, threonine, and tyrosine because of the hydroxyl group

How do disulfide bonds form

oxidation

Insulin storage

starts as an unreactive protein until it is needed, pancreas stores preproinsulin

Which amino acid is nonessential in desperate circumstances

arginine

What amino acids are essential?

His, Ile, Leu, Lys, Met, Phe, Thr, Trp, Val

How are peptide bonds formed?

dehydration

peptide bonds have slight double bond formation between N and C which causes what

rigid bond that cant rotate and bond is shorter than a single bond

The _____ C-----N bond is somewhat shorter than the _____ C----N bond

peptide; simple amine

Hydrolytic cleavage of the amide bond requires what kind of enzymes and what are two common ones and where do they cleave?

Hydrolytic enzymes

Trypsin: to the right of Arg and Lys groups

Chymotrypsin: to the right of Phe, Tyr, and Trp

How are amino acids named

start from N terminus and add -yl to group and final amino acid is normal name

structural proteins use what secondary structure

alpha helix

globular proteins use what secondary structure

beta sheets

What proteins reverse denaturation

chaperones

Prosthetic groups

non protein non amino acid groups like metals or organic materials

Ex: heme

Simple protein

no prosthetic groups, structural

Conjugated protein

have prosthetic groups

Heme structure

Iron II (ferrous) in middle of porphyrin ring

Iron binging in heme

bound to 4 nitrogens and hemoglobin by histidine, one site for oxygen

How does hemoglobin transport CO2

as carbamate

T Form (Taut) of Hemoglobin

deoxygenated, low O2 affinity

R Form (relaxed) of hemoglobin

oxygenated, high O2 affinity

Allosteric interactions

when specific molecules bind to a protein and modulates its activity

biphosphoglycerate

allosteric moderator, influence affinity of O2 for hemoglobin

Carbon monoxide poisoning

CO finds to Fe++ so hemoglobin cant bring O2 to tissues

Methemoglobin

Fe++ turns to Fe+++ > cant bind to oxygen, use antioxidants to prevent oxidation

Cyanide poisoning

messes with ETC, take methemoglobin to bind with cyanide