Exercise: Gene Expression




BIO372 : Cancer : Biology of Cancer : Gene Expression

Exercise: Gene Expression

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DUE: 28-Apr-2000 Assignments sent after the due date will receive a grade of zero.

As we have seen earlier in the semester, proteins are manufactured by the cell in a number of steps from the original information contained in the DNA of the genes.

Every cell in the body has a full complement of all genes. In cells of a particular type only a subset of the genes make their protein products because the expression of the genes is regulated.

1. The enzyme responsible for transcribing the information from DNA to the messenger RNA is RNA polymerase. For a gene to be expressed, RNA polymerase must be able to attach to the DNA molecule at a promoter site at the beginning of the gene.

One way that gene expression is regulated is to control the ability of RNA polymerase to bind to the DNA. Examples of such regulation are shown by the lac and trp genes in E. coli.

a) What difference in the structure of the repressor occurs when it binds to the lactose or tryptophan molecule that makes it possible to actively bind the operator site near the gene?

b) The regulation of the trp gene works with a negative feedback loop, i.e., like a thermostat: when there is too little tryptophan, the gene is on; when there is too much tryptophan, the gene is turned off. Explain how this regulation system manages to produce the "right amount" of tryptophan.

2. One of the tumor suppressor genes, p53, codes for a protein in the nucleus that binds to a promoter site for growth inhibitory genes. What is an hypothesis that would account for the diminished effectiveness of a mutated p53 gene?

3. When a cell lives out its life span, it dies a natural death by apoptosis. When a cell is injured, it dies by necrosis.

a) What are the main differences in cell death by necrosis and death by apoptosis?

b) Describe two instances in which cells needed in the development of an individual are naturally eliminated by apoptosis when they have served their purposes.

c) Bcl-2 is a gene in human cells that blocks apoptosis. It was listed in the reading as an oncogene. What is an hypothesis that would explain how bcl-2 contributes to some cancers?

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