Download Fall 2005 Due: 9/9 GENETICS Homework 1 1. (1 point) The

Fall 2005
Due: 9/9
GENETICS
Homework 1
1.
(1 point) The percentage of cytosine in a doublestranded DNA molecule is 40%. What is the percentage
of thymine?
2.
(1.5 points) Which of the following relations would
you expect to be true for double-stranded DNA?
a) A + T = G + C
d) A + T
C + G
3.
= 1.0
b) A + G = T + C
c) A + C = G + T
e) A + G = 1.0
C + T
(1.5 points) A nontemplate strand in bacterial DNA has
the following base sequence:
5’-ATGATACTAAGGCCC-3’
What polypeptide would be encoded by this sequence?
Give the amino and carboxyl ends.
4.
(1.5 points)
3’-ACG-5’
a.
b.
c.
An anticodon on a tRNA has the sequence
What codons could this anticodon interact with?
What amino acid is carried by this tRNA?
What would be the effect if the G in the
anticodon were mutated to a U?
5.
(2 points) A series of auxotrophic mutants were
isolated in Neurospora. Examination of fungi containing
these mutations revealed that they grew on minimal medium
to which various compounds (A, B, C, D) were added; growth
responses to each of the four compound are presented in the
following table. Give the order of compound A, B, C, and D
in a biochemical pathway. Outline a biochemical pathway
that includes these four compounds and indicate which step
in the pathway is affected by each of the mutations.
Assume that mutations showing the same rescue phenotype are
in the same gene.
COMPOUND
Mutation
Number
A
B
C
D
134
276
987
773
772
146
333
123
+
+
+
+
+
-
+
+
+
+
+
+
+
+
-
+
+
+
+
+
+
+
+
6. (1.5 points) A geneticist isolates a gene that contains
five exons. He then isolates the mature mRNA produced by
this gene. After making the DNA single stranded, he mixes
the single-stranded DNA and RNA. Some of the singlestranded DNA hybridizes (pairs) with the complementary
mRNA. Draw a picture of what the DNA-RNA hybrids would
look like under the electron microscope. Label your picture
indicating clearly where the exons and introns are.
7. (1 point) How would the deletion of the Shine-Dalgarno
sequence affect translation of a bacterial mRNA?