lecture 15- control of transcription in bacteria

what processes do antibiotics target?

cell wall synthesis, cell wall integrity, DNA synthesis, RNA polymerase, phospholipid membranes, protein synthesis

why is it important for antibiotics to target non-essential process

that it doesn’t kill the cells it just affects virulence.

describe positive and negative control of transcription

positive control:

• activator: protein that facilitates RNA Pol

• inducer: small molecule that affects activity at the activator

negative control

• repressor: prevents RNA Pol from working

• inducer: small molecule that causes the repressor to stop working

in both: effector- small molecule that regulates either repressor or activator

how do transcription factors interact with DNA

binds to the major groove (has more information)

define operon

a group of genes transcribed together

what is the role of….

CAP

operator

lac repressor

CAP: activator ; cAMP activates CAP to bind to CAP binding sites

operator: specific DNA sequence where regulatory proteins (like repressors) bind to control the operon’s expression

lac repressor: lacI; inhibits RNA Pol from binding; prevents the closed complex

what does a typical DNA binding site look like?

palendromic sequence

what is a foot printing assay

shows where DNA binds to a transcription factor

describe how the lac operon works in

a. low glucose, no lactose

b. high glucose, no lactose

c. low glucose, lactose

d. high glucose, lactose

a. lac repressor binds; no transcription; no gene expression

b. lac repressor binds; no transcription; no gene expression

c. cAMP high; high level of gene expression

d. cAMP low; low level of gene expression

what is different about the arabinose operon regulation

the same protein can act as repressor or activator depending on the conditions

AraC dimer without arabinose: AraC is a repressor by looping the DNA to prevent RNA Pol binding (represses transcription)

AraC dimer with arabinose: AraC binds arabinose and changes conformation to become activator

what is attenuation

controlling early termination of transcription in response to a signal

Trp Operon

a. what is the role of sequence 1

b. what is the role of sequence 2

c. what is the role of sequence 3

d. what is the role of sequence 4

a. codes for Trp codons ——> senses Trp levels in the cell (sensor)

b.

• when there is lots of translation in high Trp conditions it doesn’t bind to region 3

• when there is little translation it binds to region 3 to prevent region 3 from becoming a terminator

c.

• high translation. high Trp binds to region 4 to form a Rho independent terminator

• low translation, low Trp binds to region 2 no terminator is formed

d.

• high translation, high Trp binds to region 3 to form a Rho independent terminator

• low translation, low Trp doesn’t bind region 3 or form a terminator

describe an example of termination being regulated

low Trp, RNA pol transcribes whole operon of biosynthetic genes

high Trp, terminator forms + transcription is stopped