Question 1

Even though mass spectrometry has been in use for over a hundred years,it had only limited use with proteins until the 1980s because

Accepted Answer

A)  not many proteins had been discovered and purified before the 1980s.
B)  it was not possible to disperse charged proteins into a gaseous stream of particles.
C)  many proteins are difficult or impossible to crystallize.
D)  proteins decompose too quickly into their component amino acids.E) C) and D)
F) A) and C)

Question 2

At neutral pH,the net charge of serine is

Accepted Answer

A)  positive.
B)  negative.
C)  zero.
D)  None of the above.E) All of the above
F) C) and D)

Question 3

The twenty standard amino acids are the only amino acids found in living organisms.

Accepted Answer

A) True 
 B)False

Question 4

At the isoelectric pH of an amino acid which has two pKa values the net charge is

Accepted Answer

A)  0.5.
B)  1.
C)  0.
D)  -1.E) A) and D)
F) B) and C)

Question 5

Fossil dating by amino acid racemization measured

Accepted Answer

A)  the amount of a D-amino acid present.
B)  the amount of an L-amino acid present.
C)  the amounts of both D and L forms of an amino acid present.
D)  the total of all amino acids present.E) A) and B)
F) B) and C)

Question 6

What information can be gained by comparing the sequences of proteins that have the same or similar function in different species?

Accepted Answer

A)  To determine evolutionary relationships and relatedness of species.
B)  To determine sequences that are conserved among species since they are likely to be important to the function and stability of the proteins.
C)  To locate highly variable residues which contribute little to the structure and function of the protein.
D)  All of the above.E) A) and D)
F) A) and C)

Question 7

Iodoacetate is used to acetylate sulfhydryl groups to prevent their oxidation to disulfides.

Accepted Answer

A) True 
 B)False

Question 8

Which amino acid is ideal for the transfer of protons within the catalytic site of enzymes due to the presence of significant amounts of both the protonated and deprotonated forms of its side chain at biological pH?

Accepted Answer

A)  Lysine.
B)  Asparagine.
C)  Tyrosine.
D)  Cysteine.
E)  Histidine.F) A) and E)
G) All of the above

Question 9

The distribution of amino acids in a protein often cannot be determined precisely by acid hydrolysis.Why?

Accepted Answer

A)  The side chains of asparagine and glutamine are also hydrolyzed.
B)  The amine groups on lysine and arginine neutralize much of the acid.
C)  The side chain of phenylalanine is almost totally destroyed by acid hydrolysis.
D)  All of the above.E) A) and B)
F) A) and C)

Question 10

Which shows a proper peptide bond?

Accepted Answer

A)   
B)   
C)   
D)   E) B) and C)
F) A) and D)

Question 11

Although the hydroxyl groups in serine and threonine are uncharged,they can react within active sites of some enzymes ________.

Accepted Answer

A)  precisely because they are uncharged
B)  because the hydroxyl group is polar
C)  because the hydroxyl group is small and fits into the site
D)  All of the aboveE) B) and C)
F) C) and D)

Question 12

An amino acid with two chiral carbon atoms

Accepted Answer

A)  is unstable.
B)  can exist in 4 forms,all of which are superimposable.
C)  can form three possible stereoisomers.
D)  can form four possible stereoisomers.
E)  can form five possible stereoisomers.F) A) and B)
G) C) and D)

Question 13

Amino acids are neutral at the isoelectric pH.

Accepted Answer

A) True 
 B)False

Question 14

The RS system of nomenclature describes

Accepted Answer

A)  the relative sizes of molecules.
B)  the way the amino acid side chains are arranged.
C)  the absolute configuration about chiral carbon centers .
D)  the strength of the chemical groups in amino acids.E) None of the above
F) All of the above

Question 15

According to the Henderson-Hasselbalch equation,when the concentrations of proton acceptor and proton donor are the same,then

Accepted Answer

A)  the carboxylic acid is totally neutralized.
B)  only salt forms are present.
C)  pH = pKa.
D)  pKa = log[proton acceptor]/[proton donor].E) None of the above
F) All of the above

Question 16

Asparagine and glutamine are both amides of aspartic acid and because they have uncharged sidechains are often found on the interior of proteins.

Accepted Answer

A) True 
 B)False

Question 17

All 20 common amino acids have an amino group and a carboxyl group bonded to the same carbon atom.

Accepted Answer

A) True 
 B)False

Question 18

Basic amino acids are ________ (positive,negative) at pH 7 and acidic R group amino acids are ________ (positive,negative) at pH 7.

Accepted Answer

A)  negative;positive
B)  negative;negative
C)  positive;negative
D)  positive;positiveE) A) and D)
F) B) and C)

Question 19

The purpose of adding ammonium sulfate to a solution containing proteins is to cause fractionation by precipitating the less soluble proteins.

Accepted Answer

A) True 
 B)False

Question 20

Uncharged R groups of amino acids are not polar.

Accepted Answer

A) True 
 B)False

Exam 3: Amino Acids and the Primary Structures of Proteins

Iodoacetate is used to acetylate sulfhydryl groups to prevent their oxidation to disulfides.

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An amino acid with two chiral carbon atoms

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The distribution of amino acids in a protein often cannot be determined precisely by acid hydrolysis.Why?

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Which shows a proper peptide bond?

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The purpose of adding ammonium sulfate to a solution containing proteins is to cause fractionation by precipitating the less soluble proteins.

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Fossil dating by amino acid racemization measured

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Amino acids are neutral at the isoelectric pH.

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Uncharged R groups of amino acids are not polar.

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Which amino acid is ideal for the transfer of protons within the catalytic site of enzymes due to the presence of significant amounts of both the protonated and deprotonated forms of its side chain at biological pH?

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Even though mass spectrometry has been in use for over a hundred years,it had only limited use with proteins until the 1980s because

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Although the hydroxyl groups in serine and threonine are uncharged,they can react within active sites of some enzymes ________.

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The twenty standard amino acids are the only amino acids found in living organisms.

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Basic amino acids are ________ (positive,negative) at pH 7 and acidic R group amino acids are ________ (positive,negative) at pH 7.

Correct AnswerverifiedShow Answer

At neutral pH,the net charge of serine is

Correct AnswerverifiedShow Answer

According to the Henderson-Hasselbalch equation,when the concentrations of proton acceptor and proton donor are the same,then

Correct AnswerverifiedShow Answer

At the isoelectric pH of an amino acid which has two pKa values the net charge is

Correct AnswerverifiedShow Answer

All 20 common amino acids have an amino group and a carboxyl group bonded to the same carbon atom.

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What information can be gained by comparing the sequences of proteins that have the same or similar function in different species?

Correct AnswerverifiedShow Answer

Asparagine and glutamine are both amides of aspartic acid and because they have uncharged sidechains are often found on the interior of proteins.

Correct AnswerverifiedShow Answer

The RS system of nomenclature describes

Correct AnswerverifiedShow Answer

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Basic amino acids are (positive,negative) at pH 7 and acidic R group amino acids are (positive,negative) at pH 7.

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