3. (1.5 Points) a Nontemplate Strand in Bacterial DNA Has the Following Base Sequence

Fall 2005 Due: 9/9

GENETICS Homework 1

1. (1 point) The percentage of cytosine in a double- stranded 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 b) A + G = T + C c) A + C = G + T

d) A + T = 1.0 e) A + G = 1.0 C + G C + T

3. (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) An anticodon on a tRNA has the sequence 3’-ACG-5’

a. What codons could this anticodon interact with? b. What amino acid is carried by this tRNA? c. 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 single- stranded 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?