Gene Regulation

IV. Gene Regulation

Proteins, coded for by genes, can be made all of the time, only when needed, or just once. Many regulatory mechanisms exist to control gene expression.

A. Prokaryotic Gene Regulation 1. Control production of RNA, so only make polypeptides when needed (Proteins made "on demand")

2. ­ a group of genes in a region of a prokaryotic chromosome that can be controlled in a unified manner

a. :

b. Operator:

c. Structural Genes: sequences that actually code for proteins (usually enzymes)

d. Regulatory Gene (located anywhere on a chromosome): codes for protein, which controls gene expression

1 Gene Regulation

http://www.sumanasinc.com/webcontent/animations/c ontent/lacoperon.html 3. Inducible a. Normally off, but can be turned on when needed (i.e. when substrate is present)

b. : 's ability to break down lactose in glucose­deprived environment

1) Repressor (active) always bound to operator

2) If lactose is present (in high concentration), it acts as an when it combines with repressor to remove it from operator (inactivates repressor)

3) RNA polymerase can bind to promoter and transcribe structural genes to make enzyme to digest lactose

4) Lactose is digested, so lactose levels drop ­­> lactose released from repressor, so it binds back to operator

5) Gene shuts off again

2 Gene Regulation

4. Repressible Operon a. Normally on, but can be turned off when not needed (i.e. Protein needed daily so gene always on, but turns off when level gets too high)

b. trp operon: bacteria make from precursor molecule when nutrient medium lacks this amino acid

1) Genes normally on: RNA polymerase binds to promoter and transcribes genes

2) When trp levels are high, trp binds to repressor and acts as ­­> activates repressor

3) Repressor can now bind to operator and shut off genes for production of tryptophan pathway enzymes

4) When trp levels drop, trp released from repressor ­­> Inactivates repressor

5) Genes turn back on and more trp is made

3 Gene Regulation

5. Positive Gene Regulation a. cAMP accumulates when glucose is scarce

b. Regulatory protein (CAP) is an activator (binds to DNA and stimulates of a gene)

4 Gene Regulation

B. Eukaryotic Gene Regulation

5 Gene Regulation

1. Acetylation

2. DNA Methylation

6 Gene Regulation

3. Enhancers & Transcription Factors

7 Gene Regulation

4. MicroRNAs (miRNA)

C. Finding (and amplifying) genes from RNA 1. Reverse Transcriptase

2. Reverse Transcriptase­Polymerase Chain Reaction (RT­PCR)

8 Gene Regulation

9 Attachments

lac operon animation lac operon animation2 trp operon lac animation 3 trp operon 2