Topic 8

Question 1

What multiple levels of regulation affect gene expression?

Answer 1

Question 2

Define constitutive genes.

Answer 2

continuously expressed in most cells; gene products essential compounds of almost all living cells

Ex) tRNAs, rRNAs, ribosomal proteins, RNA polymerase subunits, enzymes catalyzing housekeeping functions

Question 3

Gene expression correlates with specific enzymatic requirements.
Compare catabolic pathways and anabolic pathways.

Answer 3

Catabolic pathways: breakdown substrates and activity increases after stimulus
Anabolic pathways: builds product and activity decreases after stimulus

Question 4

Regulatory proteins control transcription- what are these called?

Answer 4

transcription factors

Question 5

What is the transcription factor before the promoter than helps RNA polymerase bind and start transcription called?

Answer 5

activators and activator binding sites

Question 6

What is the transcription factor on the operator that can prevent RNA polymerase binding or starting transcription

Answer 6

repressors

Question 7

Transcription factors themselves are also regulated. How?

Answer 7

Question 8

The bacterial genome is organized in operons. What does this mean?

Answer 8

Operons coordinately regulate units of gene expression; group of genes that act like a single gene for regulation and transcription.

A single mRNA transcript carries the coding information of an entire operon; all genes in an operon are co-transcribed and therefore are coordinately expressed

Question 9

Compare an inducible operon and a repressible operon/

Answer 9

Inducible operon constitutively off until induced
A repressible operon constitutively on until induced

Question 10

Explain this chart

Answer 10

The lac operon is transcribed only in the presence of lactose because it is an inducer.
But the lac operon can only be transcribed in the presence of cAMP-CAP and this takes precedence over lactose.

So, in the presence of lactose alone it induces transcription of the metabolic enzyme by binding with the repressor protein.
In the presence of glucose alone, cAMp-CAP (a catabolic activator protein that is required to help polymerase bind) does not bind to the promoter region and thus prevents the transcription for the enzyme. Note this is because glucose is a cheaper energy and it would be a waste to produce the enzyme.
In the presence of both, glucose takes precedence over lactose and LacO is not transcribed because even though the repressor detaches from the operon, cAP-cAMP does not bind to the promoter and the polymerase doesn’t bind.

Question 11

What is the role of the Three Operators (O1, O2, and O3)?

Answer 11

Question 12

Why is enzymatic activity not as simple as on/off?

Answer 12

(1) Gene regulation is leaky- a tiny amount is produced even in a repressed system
(2) Loss of the repressor restores full gene expression
(3) Mutation of the operator only restores partial expression
(4) Multiple expressed copies of genes multiplies the enzymatic activity