Gene Regulation

Question 1

Attenuation

Answer 1

• way to couple Tc to nutrient supply-dont make genes for aa biosynthesis if you already have the aa
• common mode of regulation for aa synthesis
• leader sequence codes for peptide that functions as the attenuator
• lots of trp-make leader, Tc halted
• low trp- do not make leader, Tc goes ahead

Question 2

Trp Operon

Answer 2

• high Trp levels-the message is read quickly, favours formation of terminator (1/2, 3/4)
• low trp-ribosome stalls, favours formation of anti terminator (2/3)

Question 3

Jacques Manod

Answer 3

-worked out gene regulation for lac and trip operon

Question 4

Repressors and negative control

Answer 4

• proteins that bind DNA
• bind to specific sequences called operators
• repressors block binding of RNA pol to promoter
• ability to bind DNA is often regulated by cofactors (sugars/metabolites)

Question 5

LacZ

Answer 5

-beta galactosidase-cuts disaccharide lactose into glucose and galactose

Question 6

LacY

Answer 6

-permease-lets lactose into the cell

Question 7

LacA

Answer 7

-beta galactosidase transacetylase

Question 8

LacI

Answer 8

repressor

Question 9

P

Answer 9

promoter

Question 10

IPTG

Answer 10

artificial inducer

Question 11

Tools available to Jacob and Manod

Answer 11

• mutants (constitutive, non-inducible)
• construction of merodiploids (having a second copy of an allele), allowed for complementation
• assay for enzyme activity to tell if gene was being expressed or not

Question 12

Lac operon-Uniduced State

Answer 12

• LacI binds operator

- no Tc

Question 13

Lac operon-non-inducible mutants

Answer 13

• lacZ

- lacIs repressor can no longer bind lactose

Question 14

Lac operon-induced state

Answer 14

• inducer (lactose or IPTG) binds LacI
• LacI cannot bind operator
• Tc of operon

Question 15

Constitutive Mutants

Answer 15

• lacI-no repressor, no repression

- Oc-repressor binding site damaged, LacI is made but can’t bind

Question 16

Cis and trans mutations

Answer 16

• cis acting locus-a genetic region affecting the activity of genes on that same DNA molecule (ex. lac operator)
• transacting locus-encodes for a factor that can act elsewhere (LacI)

Question 17

Activators-positive control

Answer 17

• proteins that bind specific sequences of DNA
• make contact w/ RNA pol
• recruit holoenzyme to promoters
• classified by structure of DNA binding domain

Question 18

Diauxic shift and catabolite repression

Answer 18

• cells use glucose first
• presence of glucose represses many genes
• glucose downregulates the activity of adenylate cyclase which makes cAMP
• cAMP binds catabolite activator protein CAP
• CAP (w/ cAMP bound) is an activator that recruits RNA pol to promoters that would not be turned on efficiently otherwise

Question 19

Positive Control in lac operon

Answer 19

• subject to catabolite repression

- CAP binding site adjacent to promoter recruits pol for efficient Tc

Question 20

Negative Control-Trp Repressor

Answer 20

• operator region is bound by repressor

- repressor is only able to bind DNA when bound to Trp

Question 21

Flagella Synthesis

Answer 21

• 50 genes to make a flagella
• flagellin is among the most abundant proteins synthesized in the cell
• tightly controlled
• Tc cascade
• alternate sigma factor, sigma 28, regulates Tc of late genes

Question 22

Sigma factor-antisigma factor

Answer 22

• FliA encodes alternate sigma factor
• FliA directs polymerase to late flagellar genes
• FliA is in complex w/ FlgM (anti sigma factor)
• when hook-basal body are complete, Flgm is secreted

Question 23

Sigma 54

Answer 23

• sigma 54 RNA pol cannot form open complex on their own
• need help of NtrC at enhancer sequences far upstream from promoter
• they bind RNA pol and allow the genes to be Tc b/c of structural change in the DNA (make open complex)