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814 Chapter 26
Copyright © 2017 Pearson Education, Inc.
7.
parental DNA =
rst generation
original generation
second generation
third generation
fourth generation
8.
Thymine and uracil differ only in that thymine has a methyl substituent that uracil does not have (thymine
is 5-methyluracil). Because thymine and uracil both have the same groups in the same positions that can
participate in hydrogen bonding, they both call for incorporation of the same purine. Because thymine
and uracil form one hydrogen bond with guanine and two with adenine, they both incorporate adenine to
maximize hydrogen bonding.
9.
Because methionine is known to be the first base incorporated into the heptapeptide, the mRNA sequence
is read beginning at AUG, since that is the only codon that codes for methionine.
Met
@
Asp
@
Pro
@
Val
@
Ile
@
Lys
@
His
10.
Met-Asp-Pro-Leu-Leu-Asn
11.
It does not cause protein synthesis to stop because the sequence UAA does not occur within a triplet. The
reading frame causes the triplets to be AU
U
and
AA
A. In other words, the U is at the end of a triplet and
the next triplet starts with AA.
12.
A change in the third base of a codon is least likely to cause a mutation because the third base is variable
for many amino acids. For example, CUU, CUC, CUA, and CUG all code for leucine.
13.
The sequence of bases in the template strand of DNA specifies the sequence of bases in mRNA, so the
bases in the template strand and the bases in mRNA are complementary. Therefore, the sequence of bases
in the sense strand of DNA is identical to the sequence of bases in mRNA, except that wherever there is a
U in mRNA, there is a T in the sense strand of DNA.
5
¬
G
¬
C
¬
A
¬
T
¬
G
¬
G
¬
A
¬
C
¬
C
¬
C
¬
C
¬
G
¬
T
¬
T
¬
A
¬
T
¬
T
¬
A
¬
A
¬
A
¬
C
¬
A
¬
C
¬
3
14.
Met
Asp Pro
Val
Ile
Lys
His
codons
AUG GAU CCU GUU AUU AAA CAU
GAC CCC GUC AUC AAG CAC
CCA GUA AUA
CCG GUG