MCB Lecture 21 Gene expression

Question 0

What is regulated gene expression?

Answer 0

The gene is only transcribed under specific conditions and signals

Question 1

What is constitutive gene expression?

Answer 1

The gene is always on

This may be a housekeeping gene

Question 2

What is negative gene regulation?

What molecule causes it?

Answer 2

This is when the rate of transcription is decreased

Repressors cause this

Question 3

What is positive gene regulation?

What molecules causes it?

Answer 3

This is when the rate of transcription is increases

Activators cause this

Question 4

What are the levels of regulation in gene expression?(3)

Answer 4

Transcriptional
Post transcriptional
Post translational

Question 5

What is the role of ligand a in gene expression?

Answer 5

A ligand binds to an activator or repressor and changes the function of it

Question 6

What is a major ligand in gene expression

Answer 6

Tryptophan

Question 7

Describe the four ways that ligand a may change gene expression

Answer 7

Ligand binds to a repressor, causing it to bind to an operator. GENE OFF
Ligand binds to a repressor, inhibiting it from binding to the operator. GENE ON
Ligand binds to an activator, causing it to binding to an operator. GENE ON
Ligand binds to an activator, inhibiting it from binding to an operator. GENE OFF

Question 8

What are the two regions in the prokaryotic promoter?

What happens at these two regions?

Answer 8

-35 and -10

The sigma subunit has two prongs which bind to these regions.
The RNA pol then binds forming the holo enzyme which is ready to transcribe
Transcription starts (sigma falls off)

Question 9

Where does the sigma factor bind? What happens next?

Answer 9

To the -35 and -10 regions in the promoter

Question 10

What is an operon?

How many promoters does it have?

Answer 10

This is a region of many genes that are under the control of one promoter
They are all transcribed into one mRNA, then into many proteins

Question 11

Describe the mRNA produced from an operon and the proteins that result

Answer 11

Only one mRNA

Many proteins

Question 12

Where is an operator located?

Answer 12

In between the -35 and -10 of a promoter

Question 13

What is the function of an operator?

Answer 13

It binds activators and repressors,thus controlling transcription and gene expression

Question 14

What is a cistron? Thus, what is a poly cistron?

Answer 14

A cistron is a gene in the operon

A poly cistron is the group of cistrons

Question 15

What are cis acting elements?

Give an example of a cis acing element

Answer 15

These are regions of DNA that control the expression of a gene

Eg. Operator

Question 16

What are trans acting elements?

Give examples

Answer 16

These are factors that are mobile and interact with regions of DNA, bringing about changes in transcription and this gene expression

Eg. Activator or repressor

Question 17

How are cis and trans acting elements / factors differentiated?

Answer 17

If a cis acting element is moved, it will no longer function

This is not true for trans acting elements

Question 18

Describe the nutrition of E. coli

Answer 18

Glucose is preferred

Lactose at a push

Question 19

What is lactose broken down into, and what enzyme does this?

Answer 19

Broken down into galactose and glucose

Beta-galactosidase to break the beta-galactoside linkage

Question 20

Describe the lac operon and does it have its own promoter?

Answer 20

Yes it does

O
P
Y
Z
A

Question 21

What does lacP do?

Answer 21

This is the promoter for the operon

Question 22

What does lac O do?

Answer 22

It is the operator for the operon

Question 23

What does lac Z do?

Answer 23

Codes for beta galactosidase

Question 24

What does lac Y do?

Answer 24

Codes for the transporter that brings lactose across the membrane

Question 25

What does lac A do?

Answer 25

Removes harmful compounds

Question 26

What is the CAP binding site?

Answer 26

This binds CAP and cAMP, controlling the expression of the operon

When the CAP binding site is bound, the lac operon is expressed

Question 27

When is lac Z expressed?

Answer 27

Only expressed when there is lactose and no glucose

Question 28

Under what conditions is lacZ not expressed?

Answer 28

When there is glucose, or when there is neither glucose or lactose

Question 29

When is LacI expressed?

Answer 29

Lac I is expressed when there is no lactose

Question 30

What is the function of lacI?

Answer 30

LacI inhibits the transcription of lacZ

Question 31

Describe how and when lacI is switched off

Answer 31

When lactose is present in the cell, it acts as a ligand on the lacI repressor protein

LacI is then repressed, and transcription of lacZ occurs

Question 32

What binds to CAP binding site?

Answer 32

Cap and cAMP

Question 33

What does binding to the CAP binding site bring about?

Answer 33

Activates the lac operon

Question 34

What is the phenotype of I-?

Answer 34

No repressor for lacZ

Question 35

What is the phenotype of P-?

Answer 35

No promoter, lac operon not transcribed because RNA pol can’t bind

Question 36

What is the phenotype of O-?

Answer 36

No operator, constitutive expression because lacI can’t bind

Question 37

What is the phenotype of lacZ-?

Answer 37

No galactosidase produced, no glucose produced

Question 38

What is the phenotype of lacY-?

Answer 38

Lactose can’t get into the cell

Question 39

What is the name of the channel through which lactose passes?
What gene codes for it?

Answer 39

It is called per ease

It is coded for by LacY