What is the function of a sigma factor

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Chapters 7 & 8 Study Guide

Provide a detailed response to each essay question. With each question is a helpful hint in red. Make

sure that you answer the actual question…..not just the hint! Write out complete essays in your

BIOL241 notebook.

1. Sample #1 DNA sequence is composed of 10% T. Sample #2 DNA sequence is composed of 40% T. Which sample of DNA will denature the fastest when exposed to high temperature?

Explain why. Hint: The maximum % is 100%. What is the relationship between the number of

AT bonds and GC bonds when it comes to DNA denaturation?

2. What is the function of a sigma factor? Explain why knowing the orientation of a promoter is critical when determining the amino acid sequence of an encoded protein. Hint: What

determines which DNA strands functions as the template strand or the coding strand?

3. Why are semiconservative replication and degeneracy of the genetic code advantageous to the survival of species? Hint: Look at the genetic code of leucine. What would happen if there

was a mutation that resulted in a mRNA codon changing from CUC to CUA?

4. A student sequences DNA and discovers a point mutation in the intron of a segment coding for protein X. Explain what will be the effect of this mutation on protein X. Hint: What is the

difference between an intron and exon?

5. A student wants to study the effects of UV light-induced thymine dimers. Bacteria are exposed to UV light. If the student wants to maximize the amount of thymine dimers, she should

incubate the bacteria in the dark, light or it does not make a difference? Explain. Hint: Review

how mutations caused by UV light are repaired in bacteria.

6. Why is deleting one nucleotide generally more harmful in terms of mutational change than deleting three nucleotide? Hint: Review the types of mutations.

7. You are trying to isolate the mRNA for a gene encoding an enzyme that degrades the sugar mannitol in a species of Staphylococcus aureus. You are having problems with your

experiments because the organism does not produce the enzyme when grow under optimum lab

conditions and on complex media, such as nutrient broth or tryptic soy agar plates. Based on

your knowledge of operons in the regulation of prokaryotic gene expression, what would be the

best way to increase the amount of the desired enzyme? Explain why. Hint: Review the

regulation of inducible operons. What signal(s) are required to induce their function?

8. Why is replica plating used to isolate an auxotrophic mutant from a prototrophic parent? Hint: How are the two mutants different from one another? What mechanisms are used to isolate

them in the lab?

9. Explain why genetic changes have a more profound effect and are more easily observed in prokaryotes then in eukaryotes. Which has a longer-lived effect on a cell, a change in the

genotype or a change in the phenotype? Explain. Hint: What does it mean to be diploid?

What does it mean to be haploid? What is likely to be a more permanent effect – a change in

the DNA or a change in how the gene is expressed?

10. Why are mutation and recombination important in the process of natural selection and the evolution of organisms? Hint: What is the role of genetic diversity in natural selection and

evolution?

 
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