biochem exam questions

What is the net charge of asp when completely protonate? Assume the pKa of -NH3+ is 9.2 and pKa of -COOH is 2.1.

+1

Which of the following R groups below is valine?

-CH2(CH3)2

Which of the following R groups below is leucine?

-CH2CH(CH3)2

Which of the following correctly represents a protein backbone?

-Ca-C-N-Ca-C-N-

Which of the following peptide segments is most likely to form an α helix?

-Met-Glu-Ile-Val-Trp-Lys-Leu-Ala-

What is the net charge of glu at pH 3.9? Assume the pKa of -NH3+ is 9.2 and pKa of -COOH is 2.1.

0

What is the concentration of a protein that has an extinction coefficient of 66,000 M-1cm-1, a pathlength of 1 cm and an absorbance of 0.76

11.5uM

Consider that a hydrogen bond requires a weekly acidic donor and a weakly basic acceptor, how many donors and acceptors, respectively, does 1 water molecule have?

2 donors, 2 acceptors

IgG is one the of the five classes of antibodies. What is their subunit composition?

2 heavy chains and 2 light chains

What is the biochemical definition of steady state conditions?

25c and pH 7

How many PKA's does the tripeptide valine-histidine-tryptophan have

3

What is the pI of the dipeptide tyr-pro? Assume the pKa of -NH3+ is 9.2 and pKa of -COOH is 2.1.

5.97

Which pH is closest to neutral pH?

6.7

What is the pI of the dipeptide glu-val? Assume the pKa of -NH3+ is 9.2 and pKa of -COOH is 2.1.

7.98

How does fetal hemoglobin (Hb F) differ from normal adult hemoglobin (Hb A)?

A histidine residue in Hb A is replaced with a neutral amino acid in Hb F.

which of the following statements reaction spontaneity is false?

A reaction is said to be spontaneous when it can proceed in either the reverse or forward direction

Which of the following statements about conversion from T to R state is incorrect?

A smaller central cavity is formed when subunits displace

Which of the following is not part of the general structure of alpha amino acids?

Alpha amino group R group Hydrogen Carboxyl group Alpha carbon

Define primary structure

Amino acid sequence

Which of the following statements is incorrect?

BPG binding increases the oxygen affinity of hemoglobin.

There is a limited size of polypeptides that are observed in biological organism. Which of the following is not a reason why this is observed?

Characteristics of proteins are only dependent on amino acid composition favoring smaller polypeptides

Which of the following statements about secondary structures is true?

Coils are unique and irregular structures and are considered a type of secondary structure.

A peptide bond is formed by a ____ reaction between two amino acids.

Condensation

Which statement about 3° structure determination is false?

Cryo-EM is most suitable for measuring very small proteins.

What is denaturation

Disruption in the structure

Which of the following statements about heme properties is correct?

Fe has six coordination positions, four of which are occupied by the nitrogen atoms of the porphyrin ring.

Which of the following amino acids is not capable of forming an isopeptide bond?

Gln

Which of the following statements describes an important difference between hemoglobin (Hb) and myoglobin (Mb)?

Hb is a heterotetramer containing 2 alpha and 2 beta chains

Which amino acid has a side chain pKa of 6.04?

His

Which of the following interactions is most responsible for the maintenance of protein secondary structure?

Hydrogen bonds

The pH at which a polypeptide carries no charge is called:

Isoelectric point

Which stereochemical configuration of amino acids do proteins use?

L

Under which of the following conditions would hemoglobin have the highest affinity for oxygen?

Low bisphosphoglycerate and high pH

Which of the following amino acid combinations will have the least ability to stabilize tertiary structure?

Lys and Arg

In anion exchange chromatography, the resin is

Positively charged

In a protein, which amino acid is considered the most conformationally restricted?

Pro

Which of the following amino acids does not have absorbance in the UV range (280 nm)

Pro

Which of the following polypeptides is least likely to form a beta strand?

Ser-Glu-Asp-Asn-Phe-Gly-Ala-Pro-Lys-Ser-Ile-Leu-Trp

Which statement correctly describes oxygen binding to hemoglobin?

The binding of the first oxygen molecule enhances the binding of the other three oxygen molecules

Under which of the following conditions will hemoglobin bind less oxygen?

The concentration of carbon dioxide increases

What would be the result if a protein was treated with a chaotropic agent?

The protein would denature, and the nonpolar portions would become more soluble

Which of the following is not a type of chromatography used to separate proteins

Thin layer chromatography

Which amino acid has a side chain pKa of 10.46?

Tyr

Which of the following statements about water is false?

Water is a nonpolar molecule

Which of the options below is a naturally occurring constraint on the formation of a β-strand?

a Pro residue

Choose the correct definition of a Bronsted-Lowery base:

a proton acceptor

Which of the following answers correctly lists functional groups in the molecule shown below?

amide, hydroxyl

Proteins are made from which monomer?

amino acids

Micelles are formed from

amphiiphilic compounds with a single nonpolar tail

Hydronium ion is formed when

an additional proton is accepted by a water molecule

In an α-helix, the R groups on the amino acid residues:

are found on the outside of the helix spiral.

Which type of amino acids have absorbance that can be used to quantify them?

aromatic

A test that is highly specific for a target protein is called

assay

The first step in sequencing a protein is:

break the disulfide bonds bewteen polypeptide chains

Which one of the following functional groups has a negative formal charge?

carboxylate group

A strong acid ionizes __________________ while a weak acid ionized ________________.

completely, partially

The following reaction is nonspontaneous when it occurs at 300 K. The ΔS for the reaction is -75 J mol-1 K-1 and the ΔH is -15,000 J mol-1. Does the temperature need to be increased or decreased to make the reaction spontaneous?

decreased

Which of the following is not one of the four major levels of protein structure?

domain structure

Which of the following terms is defined as the heat exchanged in a reaction?

enthalpy

What type of cell has a membrane enclosed nucleus encapsulating DNA?

eukaryote

What two things provide efficiency in cellular functions (two answers need to be selected)?

evolved metabolic pathways, compartmentation

The amino acid composition is more important than the sequence of amino acids.

false

The _______________ law of thermodynamics states that energy is neither created nor destroyed

first

What is the function of protein disulfide isomerase?

form temporary disulfide bonds to stabilize intermediate forms

Which pair of amino acids below would interact through electrostatic interactions at pH 7.0?

glu and lys

Water organized around a substance is called a __________.

hydration shell

Which of the following forces does not contribute to protein stability.

hydrophilic affect

The center of globular proteins is composed of non-polar residues due to the

hydrophobic effect

The variable portion of the antibody sequence responsible for binding the antigens is found in the:

hypervariable loop

Which amino acid is least soluble in water?

ile

Met

interior

Which of the following statements about oxygen bound to myoglobin is correct?

is the sixth coordination link to the heme iron

Which of the statements about dialysis is true?

it is the movement of water and solutes across a a membrane

Which of the following statements about fibrous proteins is false?

keratin is a triple helix with individual right-handed helices and left-handed coiled helices.

Which statement best describes osmosis?

net movement of water across a membrane

Hypervariable region has the sequence Ala-Leu-Gly-Asn-Ile. What property would you expect an antigen to have for favorable binding at pH 7.

nonpolar

What is the net charge of gly at pH 7.0? Assume the pKa of -NH3+ is 9.2 and pKa of -COOH is 2.1.

o

Which of the following statements about structure is true?

only proteins with more than one subunit have quaternary structure

The pressure that must be applied to equalize the flow of water across a membrane in both directions is called

osmotic pressure

A protein is least soluble when:

pH = pI

monosaccharides are the monomers that make up which biological polymer?

polysaccharides

When △H is +, what must △S be for a reaction to be spontaneous. Choose all correct answers

positive if temperature is above deltaH/deltaS

When the pH is below the pKa, the functional group will always be

protonated

Which of the following statements about the protein backbone is false?

rotation occurs around the C-N and Ca-N bond

Which level of structure is defined as local spatial arrangements of the protein backbone?

secondary structure

Which of the following elements is not one of the four most abundant elements that makes up life

sulfur

His

surface

Asn

surface or interior

Which of the following statements about hemoglobin conformations is false?

the T stat of hemoglobin has a higher affinity for O2

As the concentration of {H+] in solution increases, which of the following statements are true? Select all that apply

the concentration of [OH-] decreases, the pH decreases

Which of the following is not a change in hemoglobin that occurs due to the binding of molecular oxygen?

the heme moves into the hydrophobic pocket of hemoglobin

Which of the following correctly describes why antiparallel B sheets are more stable than parallel B sheets?

the hydrogen bonding distance and angles are optimal

Mass spectrometry can help in protein sequencing by measuring:

the mass to charge ratio (m/z)

Consider a mutant hemoglobin that has a hill coefficient of 1 and p50 value that is lower than normal hemoglobin. Choose the statement below that best describes the two proteins.

the oxygen binding curve for the hypothetical hemoglobin is hyperbolic, and the curve for the normal hemoglobin is sigmoidal.

Which of the following statements correctly describes the β-sheet?

the sheets have a pleated edge on appearance (zigzag like)

What is the correct definition of the hydrophobic effect?

the tendency of water to minimize its contacts with hydrophobic molecules

Which of the following statements about molecular chaperones is false?

they can help shuttle proteins across membranes and prevent improper aggregation.

Which of the following statements about motifs is false?

β barrels can be made from a combination of β-strands and α-helices