Lehninger Biochemistry Chapter 3 Questions And Answers Graded A+ .
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Lehninger Biochemistry Chapter 3
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Lehninger Biochemistry Chapter 3
Lehninger Biochemistry Chapter 3 Questions And Answers Graded A+ .
The chirality of an amino acid results from the fact that its α carbon:
A) has no net charge.
B) is a carboxylic acid.
C) is bonded to four different chemical groups.
D) is in the L absolute configuration in na...
The chirality of an amino acid results from the fact that its α carbon:
A) has no net charge.
B) is a carboxylic acid.
C) is bonded to four different chemical groups.
D) is in the L absolute configuration in naturally occurring proteins.
E) is symmetric. - correct answer. C) is bonded to four different chemical groups.
Of the 20 standard amino acids, only ___________ is not optically active. The reason is
that its side chain ___________.
A) alanine; is a simple methyl group
B) glycine; is a hydrogen atom
C) glycine; is unbranched
D) lysine; contains only nitrogen
E) proline; forms a covalent bond with the amino group - correct answer. B) glycine; is
a hydrogen atom
Two amino acids of the standard 20 contain sulfur atoms. They are:
A) cysteine and serine.
B) cysteine and threonine.
C) methionine and cysteine
D) methionine and serine
E) threonine and serine. - correct answer. C) methionine and cysteine
All of the amino acids that are found in proteins, except for proline, contain a(n):
, A) amino group.
B) carbonyl group.
C) carboxyl group.
D) ester group.
E) thiol group. - correct answer. A) amino group.
Which of the following statements about aromatic amino acids is correct?
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. - correct answer. C) On a molar basis, tryptophan absorbs more
ultraviolet light than tyrosine.
Which of the following statements about cystine is correct?
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. - correct answer. A) Cystine forms when the —CH2—SH R group is
oxidized to form a —CH2—S—S—CH2— disulfide bridge between two cysteines.
The uncommon amino acid selenocysteine has an R group with the structure —CH2—
SeH (pKa ≈ 5). In an aqueous solution, pH = 7.0, selenocysteine would:
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. - correct answer. A) be a fully ionized zwitterion with no net
charge.
Amino acids are ampholytes because they can function as either a(n):
A) acid or a base.
B) neutral molecule or an ion.
C) polar or a nonpolar molecule.
D) standard or a nonstandard monomer in proteins.
E) transparent or a light-absorbing compound. - correct answer. A) acid or a base.
Titration of valine by a strong base, for example NaOH, reveals two pK's. The titration
reaction occurring at pK2 (pK2 = 9.62) is:
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