Regulation of Gene Expression Chapter 18

Warm Up Explain the difference between a missense and a nonsense mutation. What is a silent mutation? QUIZ TOMORROW: Transcription/Translation. Write in your own words, what happens- describing initiation, elongation and termination in each!!!

Regulation of a Metabolic Pathway A.Feedback Inhibition- inhibits the activity of the first enzyme in the metabolic pathway. A.Regulation of Gene Expression- enzymes are controlled at the transcription level, by turning genes on/off.

Operons Operator- a segment of DNA that controls the access of RNA polymerase to the genes. Found within the promoter sequence. (on/off switch) Operon- the operator, promoter, and genes they control- the entire stretch of DNA required for metabolic pathway. (trp operon)

Types of Operons Repressible Operon- usually on but can be inhibited. (Ex: trp operon) Inducible Operon- usually off but can be stimulated. (Ex: lac operon) *Both are examples of negative gene regulation.

Repressible Operons Repressor- protein that can turn off the operon by binding to the operator and blocking the attachment of RNA polymerase, preventing transcription of the genes. Regulatory Gene- codes for a repressor or similar protein that controls the transcription of another gene or group of genes. Corepressor- a small molecule that cooperates with a repressor protein to switch an operon off.

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Inducible Operons Inducer- a small specific molecule that binds to the repressor which inactivates it.

Positive Gene Regulation Activator- a protein that binds to DNA and stimulates transcription of a gene.

Exit Slip A certain mutation in E.coli changes the lac operator so that the active repressor cannot bind. How would this affect the cells production of B- galactosidase?

Warm Up Exercise Explain the difference in an inducer and a repressor operon. QUIZ TOMORROW: Transcription/Translation. Write in your own words, what happens- describing initiation, elongation and termination in each!!!

Gene Expression Differential Gene Expression- the expression of different genes by cells with the same genome. Gene expression typically refers to actions occurring in transcription, but regulation can happen at other stages in more complex organisms.

Gene Expression Histone Acetylation- acetyl groups are attached to lysines in histone tails. –Neutralizes the positive charge on the lysine which cause histones to not bind to neighboring nucleosomes. Causes chromatin to form a looser structure. Deacetylation- removal of acetyl groups.

Gene Expression DNA Methylation- methyl groups are attached to bases in the DNA (usually cytosine). –Inactive DNA is typically more methylated than regions that are actively transcribed. Individual genes are usually more methylated in cells where they are not expressed. Genomic Imprinting- expression of an allele in an offspring is determined by whether the allele is inherited by the male or female parent.

Epigenetic Inheritance Epigenetic Inheritance- inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence. –Ex: histone acetylation and DNA methylation

Regulation of Transcription Initiation Control Elements- segments of noncoding DNA that serve as binding sites for transcription factors (proteins that regulate transcription). –Proximal Control Elements (near promoter) vs. Distal Control Elements called Enhancers (upstream or downstream of a gene or within an intron)

Transcription

INSERT FIGURE 18.10

Coordinate Control in Eukaryotes Genes with the same control elements are activated by the same chemical signals. (Not by a common operator, as in prokaryotes).