Lecture 4

Question 1

Consititutive gene expression?

Answer 1

When a gene is transcribed (Expressed) at a relatively constant level under all conditions

Question 2

Regulated gene expression

Answer 2

When a gene is transcribed under certain cellular or environmental conditions

Question 3

Operons

Answer 3

In a bacterial chromosome, a group of contiguous genes that are transcribed into a single mRNA molecule

Question 4

Cistron

Answer 4

A section of DNA that contains the genetic code for a single polypeptide for a single polypeptide and functions as a hereditary unit. SO basically a gene, commonly used for pros

Question 5

Polycistron

Answer 5

Individual mRNA that encodes several different proteins, commonly found in bacteria but not euks

Question 6

Operator

Answer 6

Short region of DNA in a bacterial chromosome that control the transcription of an adjacent gene. Lies in between the -35 to -10 region. Makes up the promoter region.

Question 7

Cis acting elements

Answer 7

DNA sequences in the vicinity of the structural portion of a gene that are required for gene expression

Question 8

Trans acting elements

Answer 8

Factors, usually proteins, that bind to the cis-acting sequences to control gene expression

Question 9

What is meant when regulated gene expression can be repressed or activated?

Answer 9

Repression, negative form of control resulting in decreasing of the gene transcription.
Activation is the opposite

Question 10

Describe the 2 types of regulation, so describe negative and positive regulation and how ligand binding works

Answer 10

Negative regulation is when a bound repressor proteiin PREVENTS transcription.
Ligand binds to remove regulatory protein from DNA, so the addition of a ligand will switch ON gene transcription.
Ligand binds to allow regulatory protein to bind to DNA. So the removal of ligand switches gene on by removing repressor protein.
Positive regulation, is the same as negative but the gene is on

Question 11

downstram is wha?

Answer 11

3 to 5 on the template strand

Question 12

where does the sigma factor bind?

Answer 12

-35 to -10 region

Question 13

Where do the regulator proteins bind to in terms of region?

Answer 13

to the promoter region in a bacterial chromosome

Question 14

Tryptophan is an example of what type of regulation

Answer 14

Negative regulation where the ligand must be bound to the protein for negative regulation to take place. so bottom left corner

Question 15

Gene expression is normally regulated in response to what?Use an example for this

Answer 15

In response to changes in environment.

E coli responds to changes in salt, pH, competition, toxins, temperature, carbon source and nitrogen source

Question 16

What is the preferred carbon source for ecoli and why? but what else can it use

Answer 16

Glucose as it can easily be used for energy through glycolysis and the TCA Cycle or assimilated into various compounds required for growth.
Can use fatty acids, amino acids, lactose and glycerol

Question 17

Structure of lactose?

Answer 17

Galactose and glucose with a beta galactoside linkage

Question 18

What are the requirements for ecoli to use lactose as a carbon source?

Answer 18

Permease, Bgalactosidase enzyme

Question 19

What is permease?

Answer 19

Lactose transporter protein

Question 20

What makes up the lac operon?

Answer 20

Promoter, Operator, LacZ gene, lacY gene, lacA gene

Question 21

The following encodes what

a) lacZ
b) lacY
c) lacA

Answer 21

a) Encodes a Beta Galactosidase enzyme
b) Lactose transporter/Permease
c) Thiogalactoside transacetylase, removes toxic thios that get transported in by lacY

Question 22

Lac operon is what type of system?

Answer 22

Inducible

Question 23

Lac operon requires what for induction and what represses the expression of lac genes ?

Answer 23

Requires lactose and glucose represses the expression of the lac genes

Question 24

What is the lacI for and where is it located?

Answer 24

LacI encodes the lac repressor protein and is outside of the lac operon so its not actually part of the operon

Question 25

In the absence of lactose, the LacI does what?

Answer 25

lacI binds to the operator region and blocks RNA polymerase therefore repressing transcription

Question 26

In the presence of lactose, what happens?

Answer 26

LacI repressor disassociates from the operator and RNA poly can transcribe the operon

Question 27

What is CAP and what else does it require

Answer 27

Catabolite activator protein

and requires cAMP which is the cyclic adenosine monophosphate binds to CAP

Question 28

Where does the CAP binding site lie?

Answer 28

Before the promoter region but after the lacI

Question 29

What genes encodes the CAP

Answer 29

crp

Question 30

Changing levels of what affects the levels of cAMP

Answer 30

changing glucose levels

So high glucose levels means inactive adenylate cyclase so there is no cAMP. Opposite to activate cAMP

Question 31

CAP + cAMP is an activator protein that is required for what?

Answer 31

Expression of the lac operon

Question 32

The CAP helps what in terms of RNApol

Answer 32

Helps the RNA pol to bind the promoter

Question 33

Describe the following in relation to the lac operon and proteins etc

a) When there is no glucose present and lactose present
b) when no glucose and no lactose
c) No lactose but glucose
d) glucose and lactose

Answer 33

a) Lac Operon is expressed, everything is bound. But the lactose molecules bind to the lac repressor protein which DOESNT bind to the operator region
b) everything bound and the lacI repressor protein is also bound
c) the CAP and cAMP are not bound to its relevant site and LacI is bound. No rna pol
d) CAP not bound, RNA not bound, LacI bound to lactose but not bound to operator site

Question 34

What are the trans and cis factors of the lac operon?

Answer 34

LacI and CAP are the trans

CAP binding side and lacO operator are the Cis