Prokaryotic Gene Regulation

Question 1

What are three features of prokaryotic gene expression?

Answer 1

Gene expression is temporally separated

Transcription and translation are coupled

Translation beings while mRNA is still being synthesized

Question 2

What are three features of eukaryotic gene expression?

Answer 2

Expression is temporally and spatially separated

Transcription is in the nucleus

Translation occurs in the cytoplasm

Question 3

What are three types of temporal regulation?

Answer 3

• Increased gene expression is dependent on continued presence of an inducing signal
• Increased gene expression is transient even in the presence of regulatory signal

-Increased gene expression occurs indefinitely after signal termination
(Irreversible and inherited

Question 4

What are three mechanisms to regulate metabolic flow?

Answer 4

• Change substrate concentration
• Change the efficiency of enzyme molecules that are present
• Change the quantity of enzyme present (genetic regulation)

Question 5

What are five ways to regulate substrate availability?

Answer 5

• altering the physiological substrate concentration (Km)
• availability of metal ions and cofactors
• proximity of the enzyme
• compartmentalization
• macromolecular complexes (fatty acid synthetase)

Question 6

What are two ways to regulate enzyme activity?

Answer 6

Allosteric regulation

Covalent Modification

Question 7

What are consititutive genes?

Answer 7

Proteins that are made in fixed amounts and are required in fairly constant amounts at all times.

Question 8

What are Induced enzymes?

Answer 8

Used for the catabolism of certain nutrients only when those nutrients are present.

These enzymes are turned on when the nutrient is present.

E.g. B-galactosidase

Question 9

What are repressed enzymes?

Answer 9

Anabolic enzymes that are repressed if the end product is available in the current medium.

The enzymes are derepressed when the end product is not present.

E.g. tryptophan biosynthesis enzymes

Question 10

What is an operon?

Answer 10

The DNA sequence that contains a cluster all of the genes related to that enzyme pathway

(Regulatory, promotor, operator, cistron)

Question 11

What is a cistron?

Answer 11

All of the structural genes within the operon

Question 12

What is polycistronic mRNA?

Answer 12

Multiple proteins on the same mRNA

Question 13

What is the Shine-Dalgarno sequence?

Answer 13

Sequence within the mRNA that the ribosomes bind to

Question 14

Describe the Lac operon when lactose is absent

Answer 14

The repressor is active and bound to the operator, meaning the operon is turned off

Question 15

Describe the lac operon when lactose is present

Answer 15

Allolactose is bound to the repressor, inactivating it.

The repressor is NOT bound to the operator, meaning transcription of the operon is turned on

Question 16

What is the role of Catabolite Activator Protien (CAP) in the Lac operon?

Answer 16

When glucose is low, cAMP is high and activates CAP.

Active CAP facilitates the binding of RNA polymerase to the promotor, stimulating transcription

Question 17

What would a mutation that causes an inability of the repressor to bind the operator cause?

Answer 17

Constitutive gene expression

Question 18

What would a mutation that causes an inability of the repressor to bind the inducer molecule?

Answer 18

No gene expression because the repressor would always be active

Question 19

What would a mutation in the operator locus cause?

Answer 19

The repressor being unable to bind, causing constitutive expression

Question 20

Describe the trp operon when tryptophan is absent.

Answer 20

The repressor is inactive, allowing gene transcription to occur

Question 21

Describe the trp operon in the present of tryptophan.

Answer 21

Tryptophan acts as a corepressor and binds the repressor, activating it.

This turns the operon off.

Question 22

What is the Jacob and Monod Model?

Answer 22

The idea that an operon is a controlling unit for gene expression.

Can be used as a model for enzyme repression as well as induction.

Question 23

What is attentuation?

Answer 23

A process of regulating amino acid biosynthesis through the premature termination of mRNA synthesis

Question 24

What determines whether or not mRNA synthesis is terminated early?

Answer 24

The formation of one of several possible secondary structures

Question 25

What determines which secondary structure is formed during attentuation?

Answer 25

The rate of movement of the first ribosome to translate the message.

Question 26

Describe the effect of amino acid concentration on the rate of ribosome activity.

Answer 26

High [AA] = quick translation = premature termination

Low [AA] = slow translation = complete translation