Biology 1202B Lecture Notes - Lecture 12: Histone H3, Dosage Compensation, Heterochromatin

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olivewombat473

29 Feb 2016

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An epigenetic trait is a stably heritable phenotype resulting form changes in a chromosome without alterations in the dna sequence. Epigenetic modifications are alterations to the chromatin, talking about dna and the associated proteins, specifically histones and things that don"t alter the sequence itself. These changes take place in the cell as a result of extracellular stimuli, lead to alteration in gene expression. Environmental expressions that alter expression not the sequence. Eg. if you got muscular in the gym over the years, you don"t pass down muscular genes to your kids, however the alteration of genes will create heritable alterations. Epigenetics = regulation of gene expression o o o. Means of differential gene expression between cell types may or may not be transcribed. Epigenetic events or marks are what determine what happens, histone modification. Histone modifications and dna methylation determine if expressed or silent. Histone modifications define chromatin show you how many sites of modification there are.

Related Questions

a. Suppose you isolated a mutation in the CRP gene that results in the production of a CRP protein that cannot bind cAMP. What effect would such a mutation have on expression of the lac operon in the presence versus the absence of lactose (assume that glucose is absent in both cases)?

Answer:

b. Suppose you isolated a different mutation in the CRP gene that results in the production of a CRP protein that binds to the CRP-binding site in the lac promoter even when there is no cAMP available. What effect would this mutation have on expression of the lac operon in the presence versus the absence of lactose, if glucose were also available in both cases?

Answer:

In the following points, I have summarized Lac operon in Ecoli. I need to check if this is on the right track? and where does 'cleavage of disaccharides' fit into this picture?

Lactose is a disaccharide and the bacteria need specific genes to manage catabolism

1) The lacl promotor gene synthesis the repressor protein which binds to the operator gene stopping the RNA polymerase from coding the lac operon genes

2)But when lactose is present, it needs the specific genes to catabolise lactose

3) So, When allolactose (a derivative of lactose)is present, it binds to the repressor protein, the repressor releases from the operator gene

4) This allows the RNA polymerase can attach to the DNA control region

5) And drive down the operon for transcription and induction of the enzyme lacZ(beta-galactosidase) lacY and lacA which breaks lactose down into glucose and galactose

6) When the lactose is all gone, the repressor returns to the operator in a feedback loop system

Suppose that recombinant DNA technology was used to make a gene in which the structural genes of the lac operon were placed immediately downstream of the promoter and operator of the trp operon. This new operon is then introduced into the chromosome of an E. coli strain that does not have the normal lac operon. Therefore, the only way to get expression of Î²-galactosidase is from this artificial gene.

Bacteria with this artificial gene were grown under various conditions, and the level of Î²-galactosidase expression was measured. The effect of mutation of the trpR gene was also evaluated. The results from these experiments are given below:

presence of tryptophan	presence of glucose	presence of lactose	genotype	Level of Î²-galactosidase expression:
present	absent	present	trpR⁺ trpO⁺	low
absent	present	present	trpR⁺ trpO⁺	high
present	absent	present	trpR^- trpO⁺	high
absent	present	present	trpR^- trpO⁺	high

Can someone please explain to me in detail why the levels of Î²-galactosidase happened to turn out like this?

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Biology 1202B Lecture Notes - Lecture 12: Histone H3, Dosage Compensation, Heterochromatin

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