Question 1

Most purification procedures for proteins are carried out at room temperature.

Accepted Answer

A) True 
 B)False  False

Question 2

Ultraviolet (UV)light can be used to estimate protein solution concentrations because

Accepted Answer

A) phenylalanine absorbs at 260 nm. 
B) all the amino acids absorb UV light. 
C) aromatic amino acids absorb at 280 nm. 
D) tryptophan and tyrosine absorb at 280 nm. 
E) All of the above. 
A) phenylalanine absorbs at 260 nm. 
B) all the amino acids absorb UV light. 
C) aromatic amino acids absorb at 280 nm. 
D) tryptophan and tyrosine absorb at 280 nm. 
E) All of the above. D

Question 3

Arginine is the most basic of the 20 amino acids because its side chain is ________ under most cell conditions.

Accepted Answer

A) very highly charged 
B) hydrophobic 
C) titrated 
D) protonated 
E) negatively charged 
A) very highly charged 
B) hydrophobic 
C) titrated 
D) protonated 
E) negatively charged D

Question 4

In a biochemistry laboratory a student added ammonium sulfate to a tube containing a buffered protein solution.The student then centrifuged the solution.What was the student probably trying to do?

Accepted Answer

A) Change the pH of the buffer solution to solubilize all proteins. 
B) Hydrolyze the proteins into their constituent amino acids to determine the percent composition. 
C) Derivatize the N-terminal amino acid of all proteins. 
D) Selectively precipitate and purify a certain protein. 
A) Change the pH of the buffer solution to solubilize all proteins. 
B) Hydrolyze the proteins into their constituent amino acids to determine the percent composition. 
C) Derivatize the N-terminal amino acid of all proteins. 
D) Selectively precipitate and purify a certain protein.

Question 5

Which structure below is appropriate for glycine at neutral pH?

Accepted Answer

A) H₂NCH₂COOH 
B) H₂NCH₂COO- 
C) +H₃NCH₂COO- 
D) +H₃NCH₂COOH 
A) H₂NCH₂COOH 
B) H₂NCH₂COO- 
C) +H₃NCH₂COO- 
D) +H₃NCH₂COOH

Question 6

A mixture of four proteins (X,Y,Z and N)is applied to a gel-filtration column.Given the information supplied,which will elute first?

Accepted Answer

A)  Z 
B)  Y and N elute together 
C)  X 
D)  Cannot answer without information about the isoelectric point. 
A)  Z 
B)  Y and N elute together 
C)  X 
D)  Cannot answer without information about the isoelectric point.

Question 7

Which statement is true about SDS-PAGE of proteins?

Accepted Answer

A) The migration order for proteins in SDS-PAGE is the same as the order in gel filtration because both are sieving techniques. 
B) Some proteins migrate toward the anode and others toward the cathode. 
C) The rate of migration is inversely proportional to the logarithm of the protein's mass. 
D) SDS-PAGE is purely an analytic technique and is not used to purify proteins. 
A) The migration order for proteins in SDS-PAGE is the same as the order in gel filtration because both are sieving techniques. 
B) Some proteins migrate toward the anode and others toward the cathode. 
C) The rate of migration is inversely proportional to the logarithm of the protein's mass. 
D) SDS-PAGE is purely an analytic technique and is not used to purify proteins.

Question 8

The first treatment of a crude protein extract usually involves

Accepted Answer

A) electroplating of unwanted proteins. 
B) acidification followed by neutralization. 
C) fractionation with varying salt concentrations and centrifugation. 
D) treatment with a great number of proteases. 
A) electroplating of unwanted proteins. 
B) acidification followed by neutralization. 
C) fractionation with varying salt concentrations and centrifugation. 
D) treatment with a great number of proteases.

Question 9

A mixture of two proteins with the same pI and molecular weights (MW)of 10,000 and 15,000 daltons,respectively,are applied to a gel filtration column.What happens during elution?

Accepted Answer

A) Both elute together. 
B) The one with MW of 10,000 elutes first. 
C) The one with MW of 15,000 elutes first. 
D) More information is needed about the specificity of the column matrix to tell what happens. 
A) Both elute together. 
B) The one with MW of 10,000 elutes first. 
C) The one with MW of 15,000 elutes first. 
D) More information is needed about the specificity of the column matrix to tell what happens.

Question 10

Histidine has pKa values of 1.8,6.0 (R-group)and 9.3.At pH 8.0,the net charge on histidine is

Accepted Answer

A) positive. 
B) negative. 
C) neutral (uncharged). 
D) Insufficient information to tell. 
A) positive. 
B) negative. 
C) neutral (uncharged). 
D) Insufficient information to tell.

Question 11

When cystine is isolated after a protein is hydrolyzed,it is deduced that

Accepted Answer

A) 2 cysteine amino acids are present in the protein. 
B) the protein is linked by a disulfide bridge. 
C) 2 cysteine amino acids in the protein or proteins must be adjacent. 
D) All of the above. 
A) 2 cysteine amino acids are present in the protein. 
B) the protein is linked by a disulfide bridge. 
C) 2 cysteine amino acids in the protein or proteins must be adjacent. 
D) All of the above.

Question 12

Dialysis during protein purification is a process to

Accepted Answer

A) concentrate proteins. 
B) remove high molecular weight substances. 
C) dissolve insoluble proteins. 
D) remove low molecular weight solutes such as salts. 
A) concentrate proteins. 
B) remove high molecular weight substances. 
C) dissolve insoluble proteins. 
D) remove low molecular weight solutes such as salts.

Question 13

The pKa's of the side chain group and the α-carboxyl group of glutamate are 4.1 and 2.1,respectively.Which statement accounts for this difference?

Accepted Answer

A) The side chain has more possible resonance structures. 
B) The α-carboxyl group has less steric hindrance and is therefore ionized more easily. 
C) The side chain is a different functional group than the α-carboxyl group. 
D) The α-carboxyl group is closer to the α-amino group than the side chain is. 
A) The side chain has more possible resonance structures. 
B) The α-carboxyl group has less steric hindrance and is therefore ionized more easily. 
C) The side chain is a different functional group than the α-carboxyl group. 
D) The α-carboxyl group is closer to the α-amino group than the side chain is.

Question 14

Match the following to their functions.
-Controls the constriction of certain blood vessels

Accepted Answer

A) N-formylmethionine 
B) Histamine 
C) S-adenosylmethionine 
D) g-aminobutyrate 
E) selenocysteine
F)epinephrine (adrenaline) 
A) N-formylmethionine 
B) Histamine 
C) S-adenosylmethionine 
D) g-aminobutyrate 
E) selenocysteine
F)epinephrine (adrenaline)

Question 15

Gel-filtration chromatography separates a mixture of proteins on the basis of ________.

Accepted Answer

A) charge 
B) size 
C) affinity for ligands in the column matrix 
D) density 
A) charge 
B) size 
C) affinity for ligands in the column matrix 
D) density

Question 16

Selenocysteine,N-formylmethionine and pyrrolysine are found in many proteins.These amino acids are considered standard amino acids along with 20 common amino acids because they

Accepted Answer

A) are incorporated into proteins from specific codons. 
B) are formed by post-translational modifications. 
C) play key roles in metabolism. 
D) are precursors of other important amino acids. 
A) are incorporated into proteins from specific codons. 
B) are formed by post-translational modifications. 
C) play key roles in metabolism. 
D) are precursors of other important amino acids.

Question 17

Which substance is used to fractionate proteins based on differences in their solubility as a function of salt concentration?

Accepted Answer

A) Cellophane. 
B) Sodium dodecyl sulfate. 
C) Phenylisothiocyanate. 
D) Ammonium sulfate. 
A) Cellophane. 
B) Sodium dodecyl sulfate. 
C) Phenylisothiocyanate. 
D) Ammonium sulfate.

Question 18

Proteins can be modified by adding ________ to protein residues.

Accepted Answer

A) sugars and phosphate groups 
B) hydroxyl and formyl groups 
C) cystine 
D) A and B 
E) All of the above 
A) sugars and phosphate groups 
B) hydroxyl and formyl groups 
C) cystine 
D) A and B 
E) All of the above

Question 19

What is the N-terminal for the pentapeptide Val-Ile-Glu-Arg-Tyr?

Accepted Answer

A) The NH₃+ group on the side chain of Arg. 
B) Valine. 
C) Tyrosine. 
D) Tryptophan. 
A) The NH₃+ group on the side chain of Arg. 
B) Valine. 
C) Tyrosine. 
D) Tryptophan.

Question 20

In which technique is a protein solution pumped through a metal needle at high voltage to create tiny droplets that are analyzed for their mass/charge ratio?

Accepted Answer

A) Electrospray mass spectrometry. 
B) MALDI-TOF. 
C) Aerosol microscopy. 
D) Millikan analysis. 
E) SDS-PAGE. 
A) Electrospray mass spectrometry. 
B) MALDI-TOF. 
C) Aerosol microscopy. 
D) Millikan analysis. 
E) SDS-PAGE.

Exam 3: Amino Acids and the Primary Structures of Proteins

Most purification procedures for proteins are carried out at room temperature.

Ultraviolet (UV)light can be used to estimate protein solution concentrations because

Arginine is the most basic of the 20 amino acids because its side chain is ________ under most cell conditions.

In a biochemistry laboratory a student added ammonium sulfate to a tube containing a buffered protein solution.The student then centrifuged the solution.What was the student probably trying to do?

Which structure below is appropriate for glycine at neutral pH?

A mixture of four proteins (X,Y,Z and N)is applied to a gel-filtration column.Given the information supplied,which will elute first?

Which statement is true about SDS-PAGE of proteins?

The first treatment of a crude protein extract usually involves

A mixture of two proteins with the same pI and molecular weights (MW)of 10,000 and 15,000 daltons,respectively,are applied to a gel filtration column.What happens during elution?

Histidine has pKa values of 1.8,6.0 (R-group)and 9.3.At pH 8.0,the net charge on histidine is

When cystine is isolated after a protein is hydrolyzed,it is deduced that

Dialysis during protein purification is a process to

The pKa's of the side chain group and the α-carboxyl group of glutamate are 4.1 and 2.1,respectively.Which statement accounts for this difference?

Match the following to their functions. -Controls the constriction of certain blood vessels

Gel-filtration chromatography separates a mixture of proteins on the basis of ________.

Selenocysteine,N-formylmethionine and pyrrolysine are found in many proteins.These amino acids are considered standard amino acids along with 20 common amino acids because they

Which substance is used to fractionate proteins based on differences in their solubility as a function of salt concentration?

Proteins can be modified by adding ________ to protein residues.

What is the N-terminal for the pentapeptide Val-Ile-Glu-Arg-Tyr?

In which technique is a protein solution pumped through a metal needle at high voltage to create tiny droplets that are analyzed for their mass/charge ratio?

Introduction to Biochemistry

Water

Proteins: Three-Dimensional Structure and Function

Properties of Enzymes

Mechanisms of Enzymes

Coenzymes and Vitamins

Carbohydrates

Lipids and Membranes

Introduction to Metabolism

Glycolysis

Gluconeogenesis, the Pentose Phosphate Pathway, and Glycogen Metabolism

The Citric Acid Cycle

Electron Transport and Atp Synthesis

Photosynthesis

Lipid Metabolism

Amino Acid Metabolism

Nucleotide Metabolism

Nucleic Acids

DNA Replication, repair, and Recombination

Transcription and RNA Processing

Protein Synthesis

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