Gene Expression in Prokaryotes

Question 1

True or False - constitutive genes are continuously expressed in most cells

Answer 1

True

Question 2

Genes whose transcription status is normally on are _____ and genes whose status is normally off are _____

Answer 2

On = repressed
Off = induced

Question 3

Difference between positive and negative regulation + both their end results

Answer 3

Positive = presence of activator which allows for transcription

Negative = presence of repressor = does not allow for transcription

Question 4

What is the purpose of allosteric effectors

Answer 4

they are indicated of changes in the environment for changes the cell need to adapt to (transcriptional profile)

Question 5

Allosteric effectors bind to regulatory proteins to modulate their ______

Answer 5

affinity for DNA

Question 6

Is allolactose an effector for a repressor or activator?

Answer 6

it is an effector for repression - it changes the shape of lac repressor so it unbinds from DNA and allows for transcription

Question 7

Is cAMP/CAP an example of an effector for activation or repression?

Answer 7

It would be for activation - when the effector (cAMP) binds to CAP it can bring efficiently onto the DNA and allow for transcription

Question 8

An inducer can act on an activator or repressor protein to ____ gene expression

Answer 8

up-regulate

Question 9

A corepressor can act on an activator or repressor protein to ___ gene expression

Answer 9

Down regulate

Question 10

What are the 2 ways an inducer can induce translation?

Answer 10

1. displacing a repressor

2. enabling an activator

Question 11

What are the 2 ways a repressor can disable translation?

Answer 11

1. enabling a repressor

2. displacing an activator

Question 12

An inducible operon is constitutively ___ until ____

Answer 12

Off until induced

Question 13

an inducible + repressible operon is regulated by a _______system

Answer 13

repressor

Question 14

Steps in an inducible operon (NOOOOOOO picture)

Answer 14

1. RNA pol is blocked because the repressor is on the DNA strand
2. When the inducer is added, it forms the repressor/inducer complex
3. RNA pol can transcribe now
4. Ribosomes translating mRNA
5. Forms polypeptides

Question 15

A repressible operon is constitutively ___ until _____

Answer 15

On until repressed

Question 16

Steps in a repressible operon

Answer 16

1. RNA polymerase is translating mRNA
2. Repressor is inactive and can’t bind to the operator until co-repressor is added
3. Polypeptides are formed
   Co - repressor added - translation is blocked due to repressor/co-repressor complex

Question 17

The Lac operon is a ____ because it is usually turned off but can be turned on in the presence of ____ - _____

Answer 17

the lac operon is an inducible operon

turned on in the presence of an inducer - allolactose

Question 18

The lac operon is only expressed when ____ is present and _____ is absent

Answer 18

the lac operon is only expressed when lactose is present and glucose is absent

Question 19

Two regulatory proteins turn the operon “on” and “off” in response to lactose and glucose levels: _____ + _____

Answer 19

The lac repressor and the catabolite activator protein