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Biochemistry > L16-17: Transcription in Bacteria > Flashcards

L16-17: Transcription in Bacteria Flashcards

1
Q
A
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2
Q

What are the main drugs that target transcription in bacteria?

A

Rifampicin
Streptolydigin
Lipiarmycin

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3
Q

What are the 2 different strands of DNA known as during transcription?

A

Sense and antisense

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4
Q

Which DNA strand acts as a template in transcription?

A

The antisense strand

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5
Q

What are the 3 main regions needed during transcription?

A

1) Promotor
2) Transcribed region
3) Terminator

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6
Q

What is a main feature of bacteria during transcription?

A

It is polycistronic (encodes more than one protein, allows co-ordinated expression of a group of genes)

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7
Q

What are features of the sigma 70 promotor?

A

-upstream of txn start-site + binding site for RNA polymerase
-2 hexameric sequences at -35 and -10
-Stronger promotor means quicker initiation of txn
-Strength dictated by sequence

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8
Q

What is the consensus sequence?

A

Located at -35 and -10, closer match the promotor has to the consensus sequence the stronger the promotor is

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9
Q

What are features of RNA polymerase (RNAP)?

A

It is Mg2+ dependent and it has a multi subunit composed of:
2x alpha
1x beta
1x beta prime
1x omega

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10
Q

What are the differences between core and holoenzyme RNAP?

A

Core:
Catalyse process of transcription
Holoenzyme:
Recognises & binds to promotor
σ factor on core makes it holoenzyme
σ directs recognition of promotor sequence
σ70 is the main factor

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11
Q

What are the alternative sigma factors?

A

S- stationary phase
E- Envelope stress
F- Flagellar regulation
N- Nitrogen assimilation
H- Heat shock
FeCl- Iron metabolism

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12
Q

What happens during the formation of the txn complex for initiation and elongation?

A

Closed complex: holoenzyme binds so sense strand
Open complex: provides access to the template
Elongation

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13
Q

Which way does elongation take place?

A

5’ to 3’

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14
Q

What are features of elongation?

A

-Not as fast as replication
-RNAP has no proofreading mechanism (has backtracking ability)
-Error rate 1 in 10000

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15
Q

What are the 2 features of factor independent termination?

A

1) series of 4-10 consecutive AT base pairs
2) A G+C rich region with palindromic sequence that immediately precedes the series of AT base pairs

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16
Q

How does the G+C palindromic sequence cause termination?

A

Weakens the interaction as there is more contact with itself so it stops transcription

17
Q

What is rho dependent termination?

A

It is a helicase that unwinds RNA-DNA and RNA-RNA duplexes which is powered by ATP

18
Q

What are the 2 different ways to regulate transcription during initiation?

A

1) Repression
2) Activation

19
Q

What are activators or repressors known as?

A

DNA binding proteins

20
Q

What is the primary way to regulate transcription?

A

By regulating initiation

21
Q

What is an operon?

A

A cluster of genes under control of a single operator

22
Q

What is the lac operon?

A

Regulates the expression of genes to allow uptake of lactose to use it as an energy source

23
Q

When does high transcription of lac genes take place?

A

When lactose is present and glucose is absent

24
Q

What is the lac repressor?

A

It is the key to regulation of the lac operon
It is the product of the lacI gene
Forms a homotetramer
Binds to lac operon

25
Q

What is the lack of operator and what are key features?

A

It is the binding site for the repressor
Has a 35 bp palindrome
Has a higher affinity for binding which is more efficient than other DNA

26
Q

Why is the lac repressor a tetramer?

A

There are 3 different lac operator sites so the repressor forms a loop by binding the primary and 2 secondary operators

27
Q

How does lactose control the lac operon?

A

Lactose combines with beta-galactosides (inducer) to form allolactose which binds to the repressor causing a conformational change meaning affinity for repressor is reduced

28
Q

How does glucose influence the transcription of the lac operon?

A

Glucose inhibits the catalysis of ATP with adenylate cyclase to form cAMP so cAMP cannot bind to the CAP protein

29
Q

What happens to levels of transcription as glucose levels drop?

A

cAMP accumulates ad binds to the CAP protein as it binds to the CAP binding site which enhances the ability of RNAP to bind so transcription is activated

30
Q

What happens when glucose is present but there is no lactose?

A

No transcription, repressor binds blocking txn and CAP doesn’t bind

31
Q

What happens when no glucose and no lactose is present?

A

No transcription, repressor blocks RNAP

32
Q

What happens when glucose and lactose are both present?

A

Little transcription takes place as the repressor doesn’t bind and the CAP is not activated

33
Q

What happens when there is no glucose and lactose is present?

A

High transcription, no repressor and CAP is activated

Biochemistry (10 decks)

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