Biochemistry Chapter 4,5,& 6 Test Bank Questions
EXAM 2
The net charge of the zwitterion form of Gly is ___ - answer-Zero
When a peptide bond is formed, an ___ reacts with a carboxylate group - answer-Amino Group
At a pH above the pKa, the phenol group of tyrosine is - answer-Deprotonated
In the tripeptide Lys-Pro-Ile, there are ___ charged groups at pH 7 - answer-Three
at a pH below the pKa, the ε-amino group of lysine is - answer-Protonated
at a pH below the pKa, the β-carboxylate group of Asp is ___ - answer-uncharged; Protonated
In the peptide Trp-Ser-Val, valine is at the - answer-C-terminus
In the tripeptide Trp-Val-Phe, the N-terminal residue is ___ - answer-tryptophan
In the tripeptide Lys-Pro-Ile, the C-terminal residue is - answer-Isoleucine
Biological systems usually produce a single enantiomer, whereas chemical synthesis produces a
___ - answer-racemic mixture
GABA is a neurotransmitter derived from ___ - answer-glutamate
Glutathione is a tripeptide containing a central ___ residue - answer-Cysteine
In the early 1930's William Rose fed laboratory rats a mixture of all 19 amino acids known to be
present in proteins. He observed that his rats lost weight. This observation led to the discovery
of ____ as the 20th amino acid found in proteins - answer-Thr
What percentage of the 20 Amino acids is considered to be nutritionally essential to lab
animals? - answer-50%
About half of the 20 amino acids are called essential because - answer-Our bodies cannot
synthesize them and therefor they need to be present in our diets
Which amino acid does not have a primary α-amino group? - answer-Proline
Which of the following statements is true?
,A) Amino acids can be derived from purines
B) Purines and Pyrimidines can be derived from amino acids
C) Corn contains all 20 standard amino acids
D) Amino acids can be derived from pyrimidines
E) None of the Above - answer-B
Which of the following Amino Acids is the least abundant in proteins?
A) V
B) W
C) G
D) F
E) A - answer-B
Zwitterions are - answer-ions that bear both negatively and positively charged groups
The formation of a dipeptide from two amino acids involves... - answer-Loss of water
Which of the following amino acids has a charged polar side chain at pH 7.0?
A) Leu
B) Ala
C) Met
D) Trp
E) Glu - answer-E
Which of the following tripeptides carries a NET positive charge at pH 7.0?
A) Ala-Thr-Asn
B) Gln-Val-Ser
C) Arg-Glu-Met
D) Pro-Ile-Leu
E) Leu-Lys-Gly - answer-E
Which of the following amino acids has a sulfur atom in its side chain?
A) Asn
B) Ser
C) Phe
D) Met
E) Tyr - answer-D
Which of the following amino acids does NOT have an ionizable side chain?
, A) Asp
B) Cys
C) Lys
D) His
E) Asn - answer-E
Which of the following amino acids has an uncharged polar side chain at pH 7.0?
A) Arg
B) Thr
C) Glu
D) Pro
E) Ile - answer-B
What is the structure of Asn? - answer-
The ionization of amino acids depends on the pH and the pKas of the ionizable groups. The pK1
and pK2 for the amino acid (Asn shown in previous question) are 2.1 and 8.8, respectively. At
what pH is the amino acid ionized predominantly as shown? - answer-pH 1.0
The pK1, pK2, and pKR for the amino acid arginine are 1.8, 9.0, and 12.5, respectively. At pH 7.0
arginine would be charged predominantly as follows: - answer-α-carboxylate-1, α-amino+1,
guanidino+1, net charge +1
The pK1, pK2, and pKR for the amino acid aspartic acid are 2.0, 9.9, and 3.9, respectively. At pH
7.0, aspartic acid would be charged predominantly as follows: - answer-α-carboxylate -1, α-
amino +1, β-Carboxylate -1, Net charge -1
The pK 1 , pK 2 , and pK R for the amino acid glutamate are 2.1, 9.5, and 4.1, respectively. At
pH 11.0, glutamate would be charged predominantly as follows: - answer-α-carboxylate −1, α-
amino 0, γ-carboxylate −1, net charge −2
The pK 1 , pK 2 , and pK R for the amino acid histidine are 1.8, 9.3, and 6.0, respectively. At pH
4.0 would be charged predominantly as follows: - answer-α-carboxylate −1, α-amino +1,
imidazole +1, net charge +1
The pK 1 , pK 2 , and pK R for the amino acid cysteine are 1.9, 10.7, and 8.4, respectively. At pH
5.0, cysteine would be charged predominantly as follows: - answer-α-carboxylate −1, α-amino
+1, sulfhydryl 0, net charge 0
The pK 1 , pK 2 , and pK R for the amino acid lysine are 2.2, 9.1, and 10.5, respectively. At pH
1.0, lysine would be charged predominantly as follows: - answer-α-carboxylate 0, α-amino +1,
ε-amino +1, net charge +2
