Question 1

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

Accepted Answer

The amino acid l-proline has n...

Question 2

In a highly basic solution,pH = 13,the dominant form of glycine is:

Accepted Answer

A)  NH2-CH2-COOH.
B)  NH2-CH2-COO-.
C)  NH2-CH3+-COO-.
D)  NH3+-CH2-COOH.
E)  NH3+-CH2-COO-.F) A) and D)
G) B) and D)

Question 3

An octapeptide composed of four repeating glycylalanyl units has:

Accepted Answer

A)  one free amino group on an alanyl residue.
B)  one free amino group on an alanyl residue and one free carboxyl group on a glycyl residue.
C)  one free amino group on a glycyl residue and one free carboxyl group on an alanyl residue.
D)  two free amino and two free carboxyl groups.
E)  two free carboxyl groups,both on glycyl residues.F) D) and E)
G) A) and B)

Question 4

How can isoelectric focusing be used in conjunction with SDS gel electrophoresis?

Accepted Answer

Isoelectric focusing can separate protei...

Question 5

Which of the following statements about aromatic amino acids is correct?

Accepted Answer

A)  All are strongly hydrophilic.
B)  Histidine's ring structure results in its being categorized as aromatic or basic,depending on pH.
C)  On a molar basis,tryptophan absorbs more ultraviolet light than tyrosine.
D)  The major contribution to the characteristic absorption of light at 280 nm by proteins is the phenylalanine R group.
E)  The presence of a ring structure in its R group determines whether or not an amino acid is aromatic.F) A) and D)
G) A) and E)

Question 6

Which of the following statements 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.F) C) and D)
G) B) and E)

Question 7

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."F) B) and E)
G) B) and D)

Question 8

In the amino acid glycine,what effect does the positively charged -NH3+ group have on the pKa of an amino acid's -COOH group?

Accepted Answer

The positively charged amino group stabi...

Question 9

The uncommon amino acid selenocysteine has an R group with the structure -CH2-SeH (pKa  ≈\approx≈   5) .In an aqueous solution,pH = 7.0,selenocysteine would:

Accepted Answer

A)  be a fully ionized zwitterion with no net charge.
B)  be found in proteins as d-selenocysteine.
C)  never be found in a protein.
D)  be nonionic.
E)  not be optically active. F) A) and E)
G) A) and B)

Question 10

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

Specific activity is the units of enzyme...

Question 11

The amino acid histidine has a side chain for which the pKa is 6.0.Calculate what fraction of the histidine side chains will carry a positive charge at pH 5.4.Be sure to show your work.

Accepted Answer

Therefore,at pH 5....

Question 12

What are the structural characteristics common to all amino acids found in naturally occurring proteins?

Accepted Answer

All amino acids found in naturally occur...

Exam 3: Amino Acids, peptides, and Proteins

Which of the following statements about aromatic amino acids is correct?

Correct Answer
verified

The uncommon amino acid selenocysteine has an R group with the structure -CH₂-SeH (pK_a $\approx$ 5) .In an aqueous solution,pH = 7.0,selenocysteine would:

Correct Answer
verified

An octapeptide composed of four repeating glycylalanyl units has:

Correct Answer
verified

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?

Correct Answer
verified
Specific activity is the units of enzyme...
View Answer

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

Correct Answer
verified
The amino acid l-proline has n...
View Answer

What are the structural characteristics common to all amino acids found in naturally occurring proteins?

Correct Answer
verified
All amino acids found in naturally occur...
View Answer

Which of the following statements about cystine is correct?

Correct Answer
verified

How can isoelectric focusing be used in conjunction with SDS gel electrophoresis?

Correct Answer
verified
Isoelectric focusing can separate protei...
View Answer

In a conjugated protein,a prosthetic group is:

Correct Answer
verified

The amino acid histidine has a side chain for which the pK_a is 6.0.Calculate what fraction of the histidine side chains will carry a positive charge at pH 5.4.Be sure to show your work.

Correct Answer
verified

Therefore,at pH 5....
View Answer

In the amino acid glycine,what effect does the positively charged -NH₃⁺ group have on the pK_a of an amino acid's -COOH group?

Correct Answer
verified
The positively charged amino group stabi...
View Answer

In a highly basic solution,pH = 13,the dominant form of glycine is:

Correct Answer
verified

Exam 3: Amino Acids, peptides, and Proteins

Which of the following statements about aromatic amino acids is correct?

Correct AnswerverifiedShow Answer

The uncommon amino acid selenocysteine has an R group with the structure -CH2-SeH (pKa ≈\approx≈ 5) .In an aqueous solution,pH = 7.0,selenocysteine would:

Correct AnswerverifiedShow Answer

An octapeptide composed of four repeating glycylalanyl units has:

Correct AnswerverifiedShow Answer

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?

Correct AnswerverifiedSpecific activity is the units of enzyme...View AnswerShow Answer

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

Correct AnswerverifiedThe amino acid l-proline has n...View AnswerShow Answer

What are the structural characteristics common to all amino acids found in naturally occurring proteins?

Correct AnswerverifiedAll amino acids found in naturally occur...View AnswerShow Answer

Which of the following statements about cystine is correct?

Correct AnswerverifiedShow Answer

How can isoelectric focusing be used in conjunction with SDS gel electrophoresis?

Correct AnswerverifiedIsoelectric focusing can separate protei...View AnswerShow Answer

In a conjugated protein,a prosthetic group is:

Correct AnswerverifiedShow Answer

The amino acid histidine has a side chain for which the pKa is 6.0.Calculate what fraction of the histidine side chains will carry a positive charge at pH 5.4.Be sure to show your work.

Correct AnswerverifiedTherefore,at pH 5....View AnswerShow Answer

In the amino acid glycine,what effect does the positively charged -NH3+ group have on the pKa of an amino acid's -COOH group?

Correct AnswerverifiedThe positively charged amino group stabi...View AnswerShow Answer

In a highly basic solution,pH = 13,the dominant form of glycine is:

Correct AnswerverifiedShow Answer

Correct Answer
verified

The uncommon amino acid selenocysteine has an R group with the structure -CH₂-SeH (pK_a $\approx$ 5) .In an aqueous solution,pH = 7.0,selenocysteine would:

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
Specific activity is the units of enzyme...
View Answer

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

Correct Answer
verified
The amino acid l-proline has n...
View Answer

Correct Answer
verified
All amino acids found in naturally occur...
View Answer

Correct Answer
verified

Correct Answer
verified
Isoelectric focusing can separate protei...
View Answer

Correct Answer
verified

The amino acid histidine has a side chain for which the pK_a is 6.0.Calculate what fraction of the histidine side chains will carry a positive charge at pH 5.4.Be sure to show your work.

Correct Answer
verified

Therefore,at pH 5....
View Answer

In the amino acid glycine,what effect does the positively charged -NH₃⁺ group have on the pK_a of an amino acid's -COOH group?

Correct Answer
verified
The positively charged amino group stabi...
View Answer

Correct Answer
verified