Question 1

As a protein is purified, both the amount of total protein and the activity of the purified protein decrease. Why, then, does the specific activity of the purified protein increase?

Accepted Answer

The answer of As a protein is purified, both the...

Question 2

According to the table, ion-exchange chromatography would be the LEAST effective method to separate which protein mixture? Protein
MW
PI
A
12,500
3)2
B
13,200
5)7
C
13,500
10)5
D
25,200
6)3
E
36,900
5)8
F
78,400
6)1

Accepted Answer

A)  proteins A, B, and C 
B)  proteins A, C, and E 
C)  proteins B, E, and F 
D)  proteins B, C, and E 
E)  All of the answers are correct.

Question 3

The term "proteome" has been used to describe:

Accepted Answer

A)  regions (domains) within proteins. 
B)  regularities in protein structures. 
C)  the complement of proteins expressed by an organism's genome. 
D)  the structure of a protein-synthesizing ribosome. 
E)  the tertiary structure of a protein.

Question 4

Which statement about cystine is CORRECT?

Accepted Answer

A)  Cystine forms when the -CH2-SH R group is oxidized to form a -CH2-S-S-CH2- disulfide bridge between two cysteines. 
B)  Cystine is an example of a nonstandard amino acid, derived by linking two standard amino acids. 
C)  Cystine is formed by the oxidation of the carboxylic acid group on cysteine. 
D)  Cystine is formed through a peptide linkage between two cysteines. 
E)  Two cystines are released when a -CH2-S-S-CH2- disulfide bridge is reduced to -CH2-SH.

Question 5

Compare the following sequences taken from four different proteins, and select the answer that BEST characterizes their relationships. A
B
C
1 DVEKGKKIDIMKCS
HTVEKGGKHKTGPNLH
GLFGRKTGQAPGYSYT
2 DVQRALKIDNNLGQ
HTVEKGAKHKTAPNVH
GLADRIAYQAKATNEE
3 LVTRPLYIFPNEGQ
HTLEKAAKHKTGPNLH
ALKSSKDLMFTVINDD
4 FFMNEDALVARSSN
HQFAASSIHKNAPQFH
NLKDSKTYLKPVISET

Accepted Answer

A)  Based only on sequences in column B, protein 4 reveals the greatest evolutionary divergence. 
B)  Comparing proteins 1 and 2 in column A reveals that these two proteins have diverged the most throughout evolution. 
C)  Protein 4 is the protein that shows the greatest overall homology to protein 1. 
D)  Proteins 2 and 3 show a greater evolutionary distance than proteins 1 and 4. 
E)  The portions of amino acid sequence shown suggest that these proteins are completely unrelated.

Question 6

To determine the isoelectric point of a protein, first establish that a gel:

Accepted Answer

A)  contains a denaturing detergent that can distribute uniform negative charges over the protein's surface. 
B)  exhibits a stable pH gradient when ampholytes become distributed in an electric field. 
C)  is washed with an antibody specific to the protein of interest. 
D)  neutralizes all ionic groups on a protein by titrating them with strong bases. 
E)  relates the unknown protein to a series of protein markers with known molecular weights, Mr.

Question 7

A major advance in the application of mass spectrometry to macromolecules came with the development of techniques to overcome which problem?

Accepted Answer

A)  Macromolecules were insoluble in the solvents used in mass spectrometry. 
B)  Mass spectrometric analyses of macromolecules were too complex to interpret. 
C)  Mass spectrometric analysis involved molecules in the gas phase. 
D)  Most macromolecules could not be purified to the degree required for mass spectrometric analysis. 
E)  The specialized instruments required were prohibitively expensive.

Question 8

Why do amino acids, when dissolved in water, become zwitterions?

Accepted Answer

The answer of Why do amino acids, when dissolved in...

Question 9

Even when a gene is available and its sequence of nucleotides is known, chemical studies of the protein are still required to determine:

Accepted Answer

A)  molecular weight of the protein. 
B)  the amino-terminal amino acid. 
C)  the location of disulfide bonds. 
D)  the number of amino acids in the protein. 
E)  whether the protein has the amino acid methionine in its sequence.

Question 10

Only one of the common amino acids has no free $\alpha$-amino group. Name this amino acid.

Accepted Answer

The answer of Only one of the common amino acids...

Question 11

What is the approximate charge difference between glutamic acid and $\alpha$-ketoglutarate at pH 9.5?

Accepted Answer

A)  0 
B)  1/2 
C)  1 
D)  11/2 
E)  2

Question 12

How are "signature sequences" useful in analyzing groups of functionally related proteins?

Accepted Answer

The answer of How are "signature sequences" useful in analyzing...

Question 13

If protein A has a pI of 3.1, protein B has a pI of 6.8, and protein C has a pI of 8.9, which protein would elute FIRST from a cation exchange column at pH 7?

Accepted Answer

A)  protein A 
B)  protein B 
C)  protein C 
D)  All three proteins would elute at the same time from the column. 
E)  Not enough information about the proteins is given in the problem.

Question 14

As more OH^- equivalents (base) are added to an amino acid solution, what titration reaction will occur around pH = 9.5?

Accepted Answer

The answer of As more OH^- equivalents (base) are added...

Question 15

What is the uniquely important acid-base characteristic of the histidine R group?

Accepted Answer

The answer of What is the uniquely important acid-base characteristic...

Question 16

What is the pI, and how is it determined for amino acids that have nonionizable R groups?

Accepted Answer

The answer of What is the pI, and how is...

Question 17

The following reagents are often used in protein chemistry. Match the reagent with the purpose for which it is best suited. Some answers may be used more than once or not at all; more than one reagent may be suitable for a given purpose.
(a) CNBr (cyanogen bromide)
(e) performic acid
(b) Edman reagent (phenylisothiocyanate)
(f) chymotrypsin
(c) Sanger reagent (FDNB)
(g) trypsin
(d) reducing agent (dithiothreitol)
(h) iodoacetamide
___ hydrolysis of peptide bonds on the carboxyl side of Lys and Arg
___ cleavage of peptide bonds on the carboxyl side of Met
___ breakage of disulfide (-S-S-) bonds
___ modification of sulfhydryl groups of Cys
___ determination of the amino acid sequence of a peptide
___ determining the amino-terminal amino acid in a polypeptide

Accepted Answer

The answer of The following reagents are often used in...

Question 18

The amino acid histidine has three ionizable groups, with pK_a values of 1.8, 6.0, and 9.2. (a) Which pK_a corresponds to the histidine side chain? (b) In a solution at pH 5.4, what percentage of the histidine side chains will carry a positive charge?

Accepted Answer

The answer of The amino acid histidine has three ionizable...

Question 19

According to the diagram, does this amino acid have a titratable R-group?

Accepted Answer

A)  yes, as evidenced by the steep center of the curve 
B)  yes, as evidenced by the two relatively flat parts of the curve 
C)  no, as evidenced by only two relatively flat parts of the curve 
D)  no, as evidenced by the steepness of the center of the curve 
E)  It cannot be determined from this graph.

Question 20

In a conjugated protein, a prosthetic group is:

Accepted Answer

A)  a fibrous region of a globular protein. 
B)  a nonidentical subunit of a protein with many identical subunits. 
C)  a part of the protein that is not composed of amino acids. 
D)  a subunit of an oligomeric protein. 
E)  synonymous with "protomer."

Exam 3: Amino Acids, Peptides, and Proteins

As a protein is purified, both the amount of total protein and the activity of the purified protein decrease. Why, then, does the specific activity of the purified protein increase?

According to the table, ion-exchange chromatography would be the LEAST effective method to separate which protein mixture? Protein MW PI A 12,500 3) 2 B 13,200 5) 7 C 13,500 10) 5 D 25,200 6) 3 E 36,900 5) 8 F 78,400 6) 1

The term "proteome" has been used to describe:

Which statement about cystine is CORRECT?

To determine the isoelectric point of a protein, first establish that a gel:

A major advance in the application of mass spectrometry to macromolecules came with the development of techniques to overcome which problem?

Why do amino acids, when dissolved in water, become zwitterions?

Even when a gene is available and its sequence of nucleotides is known, chemical studies of the protein are still required to determine:

Only one of the common amino acids has no free $\alpha$ -amino group. Name this amino acid.

What is the approximate charge difference between glutamic acid and $\alpha$ -ketoglutarate at pH 9.5?

How are "signature sequences" useful in analyzing groups of functionally related proteins?

If protein A has a pI of 3.1, protein B has a pI of 6.8, and protein C has a pI of 8.9, which protein would elute FIRST from a cation exchange column at pH 7?

As more OH^- equivalents (base) are added to an amino acid solution, what titration reaction will occur around pH = 9.5?

What is the uniquely important acid-base characteristic of the histidine R group?

What is the pI, and how is it determined for amino acids that have nonionizable R groups?

The amino acid histidine has three ionizable groups, with pK_a values of 1.8, 6.0, and 9.2. (a) Which pK_a corresponds to the histidine side chain? (b) In a solution at pH 5.4, what percentage of the histidine side chains will carry a positive charge?

According to the diagram, does this amino acid have a titratable R-group?

In a conjugated protein, a prosthetic group is:

Exam 3: Amino Acids, Peptides, and Proteins

As a protein is purified, both the amount of total protein and the activity of the purified protein decrease. Why, then, does the specific activity of the purified protein increase?

According to the table, ion-exchange chromatography would be the LEAST effective method to separate which protein mixture? Protein MW PI A 12,500 3) 2 B 13,200 5) 7 C 13,500 10) 5 D 25,200 6) 3 E 36,900 5) 8 F 78,400 6) 1

The term "proteome" has been used to describe:

Which statement about cystine is CORRECT?

To determine the isoelectric point of a protein, first establish that a gel:

A major advance in the application of mass spectrometry to macromolecules came with the development of techniques to overcome which problem?

Why do amino acids, when dissolved in water, become zwitterions?

Even when a gene is available and its sequence of nucleotides is known, chemical studies of the protein are still required to determine:

Only one of the common amino acids has no free α\alphaα -amino group. Name this amino acid.

What is the approximate charge difference between glutamic acid and α\alphaα -ketoglutarate at pH 9.5?

How are "signature sequences" useful in analyzing groups of functionally related proteins?

If protein A has a pI of 3.1, protein B has a pI of 6.8, and protein C has a pI of 8.9, which protein would elute FIRST from a cation exchange column at pH 7?

As more OH- equivalents (base) are added to an amino acid solution, what titration reaction will occur around pH = 9.5?

What is the uniquely important acid-base characteristic of the histidine R group?

What is the pI, and how is it determined for amino acids that have nonionizable R groups?

The amino acid histidine has three ionizable groups, with pKa values of 1.8, 6.0, and 9.2. (a) Which pKa corresponds to the histidine side chain? (b) In a solution at pH 5.4, what percentage of the histidine side chains will carry a positive charge?

According to the diagram, does this amino acid have a titratable R-group?

In a conjugated protein, a prosthetic group is:

Only one of the common amino acids has no free $\alpha$ -amino group. Name this amino acid.

What is the approximate charge difference between glutamic acid and $\alpha$ -ketoglutarate at pH 9.5?

As more OH^- equivalents (base) are added to an amino acid solution, what titration reaction will occur around pH = 9.5?

The amino acid histidine has three ionizable groups, with pK_a values of 1.8, 6.0, and 9.2. (a) Which pK_a corresponds to the histidine side chain? (b) In a solution at pH 5.4, what percentage of the histidine side chains will carry a positive charge?