Before the eluant from the column is collected in the fraction collector: Select

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Before the eluant from the column is collected in the fraction collector:

Select one:

a. It is mixed with a buffer to lower the ion concentration

b. It passes through a spectrophotometer

c. It is heated for a short period and sterilized

d. It is first collected in a large cylinder and then dispensed into smaller vials

e. All of the above

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In SDS-PAGE, the protein sample is typically treated with a reducing agent. This treatment allows-

Select one:

a. To separate large polypeptides from small polypeptides

b. To denature proteins

c. To separate a multi-subunit protein to its individual polypeptides

d. To accelerate the formation of disulfide bridges in the proteins

e. None of the above

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Which of the following interactions is NOT a basis for an affinity chromatography procedure?

Select one:

a. Antigen-antibody

b. Hormone-receptor

c. DNA- transcription factor

d. Negative charge- positive charge

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At any pH below the pI of the amino acid glycine, it will have:

Select one:

a. A net positive charge

b. A zero net charge.

c. A net negative charge.

d. One fully positive and one fully negative charge

e. its both carboxyl- and amino groups half dissociated

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The graph depicts the elution profile from a CM-cellulose (ion exchange) resin. Which of the proteins bound the least tightly to the resin?

Select one:

a. X

b. 1

c. 2

d. 5

e. can't tell from the information provided

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The graph above depicts the elution profile from a DEAE-cellulose (ion exchange resin). The peaks labeled "1" through "5" consist of:

Select one:

a. Positively charged amino acids

b. Neutral amino acids

c. The amino acids that did not bind to the column

d. Negatively charged amino acids

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The functional differences, as well as differences in three-dimensional structures, between two different enzymes from e. coli result directly from their different:

Select one:

a. affinities for ATP.

b. amino acid sequences.

c. roles in DNA metabolism.

d. roles in the metabolism of e. coli.

e. secondary structures.

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A protein has a molecular mass of 200 kDa as determined by gel filtration (=native molecular weight). When separated by SDS-PAGE (without a reducing agent present) only one polypeptide appeared with a mass corresponding to 100 kDa. When determined by SDS-PAGE in combination with a reducing agent (DTT) exactly two polypeptides appeared of sizes 40 and 60 kDa. What is the correct structure of the native protein?

Select one:

a. The native protein is made of one 40 kDA and one 60 kDA polypeptides

b. The native protein is made of two 100 kDa polypeptides

c. The native protein is made of two 40 kDA and two 60 kDA polypeptides

d. The native protein is made of four polypeptides - two 100 kDa polypeptides, one 40 kDA and one 60 kDA polypeptides

e. None of the answers is correct.

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Free amino acids are different from their residues in proteins by-

Select one:

a. The size of the R group

b. Having a lower molecular weight

c. Being larger by the size of a water molecule

d. 110 daltons

e. None of the above

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Four proteins, each containing a single polypeptide, are separated by SDS-PAGE: human cytochrome c (MW 13,000), human serum albumin (MW 67,000), bovine myoglobin (MW 16,890), and human apolipoprotein B (MW 513,000). Which one would show up as the band at the bottom of the gel?

Select one:

a. cytochrome c

b. apolipoprotein B

c. bovine myoglobin

d. serum albumin

e. can't tell from the data provided.

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The peptide alanylglutamylglycylalanylleucine:

Select one:

a. Will be easily dissolved in an aqueous solution .

b. has five peptide bonds.

c. Has no free carboxyl group.

d. Is mostly hydrophobic

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The pentapeptide leucylglycylthreonyltyrosylalanine is first incubated with l-fluoro-2,4-dinitrobenzene (FDNB). When the resulting compound is heated to 110oC for 24 h in the presence of 6 M HCl, the solution will contain:

Select one:

a. one alpha-amino acid labeled by FDNB and an unlabeled tetrapeptide.

b. five alpha-amino acids with only alanine labeled by FDNB.

c. all five alpha-amino acids, each labeled by FDNB.

d. all five alpha-amino acids, but only lysine will be labeled by FDNB.

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In affinity chromatography, the bound proteins are typicallty eluted by a solution containing:

Select one:

a. Salt

b. Ligand

c. Acid

d. A and B

e. A, B, and C

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Which of the following is FALSE with respect to the amino acid composition of proteins?

Select one:

a. Proteins that are closely related by evolution tend to have similarities in their composition and sequence

b. Most proteins contain at least one each of the 20 different standard amino acids.

c. Amino acid composition vary between proteins that have different functions

d. Proteins with the similar molecular weights tend to have similar amino acid composition.

e. Proteins that contain more than one domain usually have more than one function

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Which of the following pentapeptides is expected to be the BEST dissolved in water?

Select one:

a. NH2 - ser - pro- gly - ala- cys - asn - COOH

b. NH2 - tyr - thr - gly - ser - gln - asp - COOH

c. NH2 - ser - ala - gly - phe - gln - asp - COOH

d. NH2 - gly - leu - phe - val - ser - gly - COOH

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We have isolated an unknown human protein. By determining the amino acid sequence of a 15-25 residue-long portion of it we can-

Select one:

a. Tell what is the biological function of the protein

b. Find the gene coding for the protein by searching the genebank database

c. Compute the precise 3-D structure of the protein

d. All of the above

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

Select one:

a. cleavage

b. ester formation

c. group transfer

d. dehydration

e. oxidation reduction

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Electrophoresis in the presence of SDS separates proteins almost exclusively on the basis of:

Select one:

a. Mass

b. Charge

c. Shape

d. Polarity

e. Solubility

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The following compound is-

Select one:

a. FDNB

b. PITC

c. Phenylalanine

d. Histidine

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Dr. Strangelab performed peptide mapping to a polypeptide he had purified by using a protease. All the fragments had either arginine or lysine residues at their C terminal end. The polypeptide Dr. Strangelab used -

Select one:

a. Must have been a mixture of two different polypeptides

b. Could not have been cleaved by trypsin

c. Was definitely one to bind a cation-exchange column

d. Had either arginine or lysine residues at its C-terminal end

Question 21

In a mixture of the five proteins listed below, which should elute FIRST in size-exclusion chromatography?

Select one:

a. cytochrome c, Mr = 13,000

b. immunoglobulin G, Mr = 145,000

c. ovalbumin, Mr = 43,000

d. RNA polymerase, Mr = 450,000

e. serum albumin, Mr = 68,500

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The reagent used in the Edman degradation is-

Select one:

a. PITC

b. FDNB

c. DTT

d. Urea

e. None of the above

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Why is column chromatography performed at the end of every cycle of Edman degradation?

Select one:

a. To completely purify the amino acid

b. To determine the molecular weight of the amino acids

c. To find out the name of a labeled amino acid by its point of elution from the column

d. To separate between the polypeptides

e. To separate the labeled amino acid from the unlabeled ones

Question 24

To cleave a polypeptide next to a tyrosine residue, one can use which of the following enzymes-

Select one:

a. chymotrypsin

b. invertase

c. RNA polymerase

d. trypsin

e. CNBr

Question 25

Proteases are useful in sequencing because-

Select one:

a. There is a protease to cut near any of the twenty amino acids

b. After a protein is digested by a protease it is completely destroyed and there is no need to sequence it any longer

c. Protease digestion generates fragments of equal sizes along the original length of the protein.

d. All of the above

e. None of the above

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Molecules that differ in size can be separated from each other by which of the following methods-

Select one:

a. Ion exchange chromatography

b. Affinity chromatography

c. gel-filtration chromatography

d. A, B, and C

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The flow-through fraction in ion exchange chromatography of amino acids in which a anion exchange resin was used is expected to contain mainly:

Select one:

a. Negatively charged amino acids

b. Positively charged amino acids

c. Polar amino acids

d. Non-polar amino acids

e. All the answers are correct

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Which method of protein chromatography can accomplish the greatest level of purification in a single step:

Select one:

a. SDS-PAGE

b. affinity chromatography

c. hydrophobic chromatography

d. gel-filtration

e. ion exchange

Explanation / Answer

Q1). b. It passes through a spectrophotometer

Before the eluant from the column is collected in the fraction collector, it passes through a spectrophotometer or mass spectrometer to determine its concentration.

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