MBG*2040 Molecular Biology Assignment #8

25 Jun MBG*2040 Molecular Biology Assignment #8

Question

MBG*2040 Molecular Biology Assignment #8

Tutorial assignment for Mutation, DNA repair and recombination

Sheet #1

Name: __________________________________________ID#_____________

Tutorial Day and Time:____________________________________________

TA Name:_______________________________________________________

Chapter 13: Lecture Topics

Sources of Genetic Variability
The Molecular Basis of Mutation
DNA Repair Mechanisms

The assignment questions are based upon information presented in lectures on these topics. To enhance understanding and develop analytical skills, students are also encouraged to peruse the basic exercises and problems at the end of Chapter 13.

Assignment questions to be answered in advance of the tutorial. A codon table is provided.

1 a) List the purine bases:

b) List the pyrimidine bases:

c) Distinguish between a transition and a transversion mutation

d) What is a tautomeric shift?

e) Tautomeric shifts usually result in transition mutations. Is this statement correct? Explain.

2. The X-linked gene that encodes the enzyme glucose-6-phosphate dehydrogenase (G6PD) is 18 kilobase pairs, with 13 exons. The enzyme has a molecular mass of 58 kDa and consists of 531 amino acids. A man has a null allele of the G6PD gene. Analysis of the DNA sequence of the man’s G6PD gene indicates that there is a 5’CAT to 5’GAT change in the non-template DNA strand of exon 8 which results in an amino acid substitution in position 282 of the enzyme. The next two questions are based on this information.

a) The mutation results in an amino acid change from ____________ to _______________.

b) Which of the terms below best categorizes the man’s mutation? Support your answer.

i. Missense mutation caused by a transition.

ii. Missense mutation caused by a transversion.

iii. Nonsense mutation caused by a transition.

iv. Nonsense mutation caused by a transversion.

v. Frameshift mutation.

vi. Silent mutation.

3. A small portion of a hypothetical mRNA encoded from a wildtype gene has the sequence,

5′ AUGAAUCAGCCGUUACCCGUA 3′. This mRNA encodes the polypeptide fmet-asn-gln-pro-leu-pro-val.

a) A transition mutation occurred in the DNA at the nucleotide position indicated by the underlined C. What will be the sequence of the polypeptide produced by this mutant?

b) A transversion mutation occurred in the DNA at the nucleotide position indicated by the underlined U. What will be the sequence of the polypeptide produced by this mutant?

c) Categorize a) and b) as to whether these are silent, nonsense, missense or frameshift mutations.

4. The nucleotide sequence of a portion of the coding region of the template strand of a protein-encoding gene is 5′ CATACCGA 3′. A mutation deletes a single base pair which removes the single G from the template strand. Three students suggest possible ways in which this mutation could be suppressed. Which one is correct (and why)?

a. Melanie claims a second base pair deletion, close to but downstream from the original mutation within the same gene, will suppress the above mutation.

b. Liz claims a second mutation which adds a base pair, close but downstream from the original mutation within the same gene, will suppress the above mutation.

c. Wayne claims a second mutation which deletes exactly three base pairs, close to but downstream from the original mutation, will suppress the above mutation.

5. Of all possible missense mutations that can occur in the segment of DNA encoding the amino acid tryptophan, what is the ratio of transversions to transitions if all single base-pair substitutions occur at the same frequency?

UNIVERSAL GENETIC CODE TABLE
2nd position

U C A G

U

Phe

Phe

Leu

Leu

Ser

Ser

Ser

Ser

Tyr

Tyr

Stop

Stop

Cys

Cys

Stop

Trp

U

C

A

G

1st position

C
Leu

Leu

Leu

Leu

Pro

Pro

Pro

Pro

His

His

Gln

Gln

Arg

Arg

Arg

Arg

3rd position

U
C

A

G

A

Ile

Ile

Ile

Met

Thr

Thr

Thr

Thr

Asn

Asn

Lys

Lys

Ser

Ser

Arg

Arg

U

C

A

G

G

Val

Val

Val

Val

Ala

Ala

Ala

Ala

Asp

Asp

Glu

Glu

Gly

Gly

Gly

Gly

U

C

A

G