3.6: Regulating gene expression + Lac/Mal operons

Question 1

Two mechanisms of gene regulation

Answer 1

Induction: Signal molecule promotes gene expression (i.e., catabolic genes - enzyme needed to break down lactose = only expressed when lactose is present)
Repression: Signal molecule inhibits gene expression (i.e., anabolic genes - enzyme needed to synthesize amino acid = presence of amino acid stops gene expression)

Question 2

Constitutively expressed vs Environmentally regulated genes

Answer 2

Expressed all the time (even at low levels) vs expressed at high levels only under certain environmental conditions

Question 3

What is a operon

Answer 3

Region of DNA that codes for a series of functional genes which shares a single promoter.

Question 4

DNA regulatory region

Answer 4

Specific nucleotide sequence near/partially overlapping the promoter sequence of an operon.
Common example is the operator.

Question 5

Regulatory genes/proteins

Answer 5

Binds to the DNA regulatory region. Determines if RNA polymerase can initiate transcription.
Constitutively expressed at low levels and are usually not part of the operon.

Question 6

Signal molecules and regulatory genes/proteins

Answer 6

Regulatory proteins are allosteric, and adopts different shapes depending on if signal molecules bind or not.
This binding determines whether or not the regulatory protein can bind to the regulatory region on the operon.

Question 7

Positive vs negative operon regulation

Answer 7

Same concept as inducer vs repressor
Positive: Regulatory gene/protein ACTIVATES gene expression. Thus, they are called activators.
Negative: Regulatory gene/protein inhibits gene expression. They are now repressors.

Question 8

Polycistronic mRNA

Answer 8

mRNA that codes for more than one protein, the product of an operon.
Usually codes for products that are needed in successive steps for either a synthesis or a breakdown of a molecule.