Operon

Question 1

What does ChIP-seq measure?

Answer 1

Protein-protein interaction specifically

Question 2

Define regulatory gene

Answer 2

Genes coding for product that control expression of other genes

Question 3

Define operon

Answer 3

Unit of bacterial gene expression and regulation = includes structural genes and control elements in DNA recognized by regulatory gene products

Question 4

Define cis-acting elements

Answer 4

Exerts their regulatory influence only on adjacent genes on the same chromosome

Examples = promoters, enhancers, silencers

Question 5

Define trans-acting proteins

Answer 5

Regulatory proteins/molecules that can diffuse through the cell and exert their regulatory influence on genes located at distant chromosomal locations

Examples = transcription factors and RNA-binding proteins

Question 6

Define negative transcriptional control

Answer 6

Repressor protein bind operator = preventing gene from being expressed

Question 7

Define positive transcriptional control

Answer 7

Activator (TF) = required to bind at promoter To enable RNAp to initiate transcription

Question 8

What are genes located adjacent rto each other transcribed into?

Answer 8

Polycistronic mRNA

Question 9

What does the lac operator overlap?

Answer 9

Promoter at the start of the cluster (PO)

Question 10

What doe lac I code for and have?

Answer 10

Lac repressor = has its own promoter and terminator

Question 11

What genes does the lac repressor control

Answer 11

lacZYA

Question 12

What controls the lac repressor?

Answer 12

Inducer

Question 13

What is the natural inducer?

Answer 13

1,6-allolactose

Question 14

What is the role of the inducer?

Answer 14

Converts repressor to form with lower operator affinity
This allows RNAp to initiate transcription

Question 15

What is the lac operon gratuitous inducer?

Answer 15

IPTG = not metabolized

Question 16

What is a gratuitous inducer?

Answer 16

Can induce the expression of a gene or set of genes in an organism, typically in a manner similar to a natural inducer

But without providing any benefit or nutritional value to the organism.

It is an inducer molecule that is not normally encountered or utilized by the organism in its natural environment.

Question 17

What are the lac repressors binding sites?

Answer 17

Binds to operator DNA and inducer

Question 18

Repressor dimers form a tetramer by interaction between what?

Answer 18

Interactions between oligomerization helices

Question 19

What does the N-terminal DNA-binding domain consist of?

Answer 19

2 alpha-helical regions = helix-turn-helix
This binds to MAJOR groove of DNA

Question 20

What is located at the core of the lac repressor?

Answer 20

Inducer-binding site
And reigons responsible for multimerization

Question 21

Describe the operator the lac repressor binds to

Answer 21

Palindromic sequence of 26 bp

Question 22

What does inducer binding to repressor cause?

Answer 22

Change in repressor conformation
Reducing affinity for DNA and releases it from the operator

Question 23

What happens in the case of mutations in the operator (Oc)?

Answer 23

Constitutive expression of all 3 genes
Because operator is unable to be bound with repressor protein
Allowing RNAP to have unrestrained access to promoter

Question 24

Oc mutation = cis-dominant, what does this mean?

Answer 24

Operator can control only the gene adjacent to it
These mutations are cis-acting and effect only those genes on the contiguous stretch of DNA

Question 25

What happens in lacI- mutation?

Answer 25

Mutation that inactivates the lacI genes
Repressor cannot bind to the operator

Induction of a normal lacI+ gene can restore control even in the presence of a defective lacI- gene

Recessive

Question 26

What is lacIs?

Answer 26

Super suppressor
Mutation in inducer-binding site of the repressor
Binds the operator and prevents transcription because cannot be removed

Uninducibility

Question 27

What is lac-d?

Answer 27

Dominant

Mutations in DNA-binding site of the repressor

Repressor cannot bind the operator = constitutive

Question 28

Why is lac-d dominant?

Answer 28

Mutant subunits can bind with normal subunits
Only requires one of the subunits to be mutant to block repressor function = cannot bind DNA

Explains dominant negative behaviour

Question 29

Which operator does the lac repressor have the highest affinity for?

Answer 29

O1

Question 30

What is the second layer of control for the lac operon?

Answer 30

Catabolite repression

Question 31

What is catabolite repression?

Answer 31

Ability of glucose to prevent the expression of a number of genes

Question 32

What is the other name for CAP?

Answer 32

cAMP receptor protein = CRP
Catabolite activator protein = CAP

Question 33

What is the role of cAMP in regards to CRP?

Answer 33

cAMP converts inactive CRP to a form that binds the promoter
Assists RNAP in initiating transcription

Question 34

How does glucose cause catabolite repression?

Answer 34

When glucose is high = low cAMP

Preventing:
cAMP activates a DIMER of CRP
CRP interacts with the CTD of the alpha subunit of RNAP to activate it

So RNAP not activated in the end

Question 35

What are the lacC, P, O sites?

Answer 35

CAP binding site
Promoter = CAP-dependent
Operator = repressor binding site

Question 36

What are the genes of the lac operon?

Answer 36

lacZ = beta-galacosidase, stains colonies blue
lacY = permease, transports lactose
lacA = transacetylase

Question 37

How is the lac+ phenotype examined?

Answer 37

Nutrient agar containing IPTG and X-gal
X-gal cleaved by beta-galactosidase = blue

So if the lac+ is working = there should be blue because the enzyme is produced