Biology 1202B Lecture Notes - Lecture 15: Histone Code, Heterochromatin, Euchromatin

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13 Mar 2017

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Lecture 15 - regulation of gene expression ii. Many genes involved in the same biochemical process. A mechanism by which these genes can be controlled. This is how prokaryotes organize their genome. The promoter is a promoter for all the genes in the operon. They are transcribed as a single unit, and then translated into 3 different proteins. Plays a significant role in regulating which genes are turned on and off in a cell. These epigenetic modifications are stable and heritable, which results in changes to chromatin w/o alterations in the dna sequence. A way that cells/organisms can respond to environmental stimuli by regulating gene expression, which can be passed on through dna replication. Euchromatin is potentially active chromatin; can be transcribed. Heterochromatin is bound w/ proteins and densely packed; transcriptionally silent. Epigenetic modifications signal whether dna should be euchromatic or heterochromatic. Their primary method of action is through chromatin. Histones are proteins, which have n and c terminal tails.

Related Questions

What role do insulator sequences play in the regulation of eukaryotic transcription?

A		They block communication between enhancers and nontargeted promoters
B		They block binding of transcription factors to cis-acting promoter elements
C		They block binding of transcription repressors to cis-acting promoter elements
D		They block binding of transcription factors to enhancers
E		They block binding of transcription factors to silencers

What would be the effect of a mutation in the lacI gene that prevented the repressor from binding to lactose?

A		The lac Z, Y, and A genes would not be expressed.
B		The lac Z, Y, and A genes would be expressed constitutively
C		The lac Z, Y, and A genes would be repressed by lactose.
D		The lac Z, Y, and A genes would be induced by lactose.
E		The lac Z and Y genes would be repressed but not the lac A gene.

maroonferret375

1) In the wildtype (the DNA sequence most commonly found in nature) lac operon, transcription is severely down-regulated. A mutation in lacI that causes an early stop codon in the sequence (called a lacI - strain) results in an operon that has high levels of transcription of the polycistronic m-RNA. What type of regulatory protein is the LacI protein (hint: we covered this type of protein in lecture)?

The Lac regulatory protein is called a repressor. (is this correct)

2) If a bacterium with a wildtype lac operon is grown in the presence of lactose, high levels of transcription result for a while, however, eventually transcription is again down-regulated. If, on the other hand, the sugar IPTG is present (instead of lactose), transcription levels are high and remain high. What function do IPTG and lactose share? How are they differently affected by the operon product? (need help with this question)

Lactose and IPTG affected by the operon are both inducers of the Lac-Operon. (is this correct)

3) What is âepigeneticsâ? What forms of gene regulation are usually involved in epigenetic control of a trait? Why do we have such a limited understanding of epigenetic processes? (need help with this question)

Epigenetics is the study of phenotype changes that do not change the DNA sequence. Genes can be turned on and off based on environment situations of past generations, (parents or even grandparents) were exposed. Examples of some environmental factors could be diet, stress, smoking, drinking alcohol, and diseases. Histone modification and methylation are usually involved in epigenetic control of a trait. (is this correct)

18) In your research on gene regulation in E. coli, you produce 2 mutant strains with the same phenotype: they can grow on lactose but not on glucose. To investigate these 2 mutants further, you perform a complementation test using them and discover that the diploid combination strain can grow on glucose or lactose. From this, you can deduce that:

a.)Both mutants have a mutation in the same gene

b.)The 2 mutants have mutations in different genes
c.)Glucose and lactose metabolic pathways in E. coli utilize at least one shared gene in common
d.)At least 2 different genes are required for glucose metabolism in E. coli
e.) b) and d)

19. In your research on the lac operon, you produce a unique regulatory mutatant strain of E. Coli where the lac l gene's repressor protein binding site for the operator is normal (wild-type) but its lactose binding site no longer binds lactose. The expected phenotype of this mutant will be:

a. inability to grow on lactose only medium

b. ability to grow on lactose only medium

c. blue colony color when grown on glycerol plus x-gal medium

d. blue colony oclor when grown on lactose plus x-gal medium

e. b & d

20.

20) In your research on the lac operon, you create a diploid E.coli strain with the following genotype (+) = wild type gene, (-) = mutant gene.

I- /O+ /Z- /Y+

I+ /Oc /Z+ /Y+
Can this diploid mutant grow on medium containing lactose as the only carbon source?

a) Yes

b) No

c) Maybe, it depends on if the Oc mutation is dominant or recessive

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Biology 1202B Lecture Notes - Lecture 15: Histone Code, Heterochromatin, Euchromatin

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