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Genetics EXAM 3 > Chapter 10 - Bacterial Gene Expression Control > Flashcards

Chapter 10 - Bacterial Gene Expression Control Flashcards

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1
Q

Promoter

A

Eukaryotes and Prokaryotes can diff ones.

This is where transcription begins.

It is a region on DNA when RNA polymerase binds to start transcription

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2
Q

Sigma Factor

A

a protein that binds to specific DNA sequences at the promoter to initiate transcription.

binds to two regions

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3
Q

What two regions does the sigma factor bind to

A

Pribnow Box (-10 element): TATAAT
helps find the start point

-35 element: sequence TTGACA
helps stabilize

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4
Q

RNA polymerase recruitment

A

sigma factor recruits RNA polymerase to the promoter and transcription begins

then sigma factor falls off

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5
Q

Termination Sequence

A

The sequence where transcription stops, typically containing a GC-rich region and a series of uracils (U) in the RNA.

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6
Q

Hairpin Loop

A

The GC-rich sequence in the RNA forms a hairpin structure that causes RNA polymerase to dissociate and terminate transcription.

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6
Q

RNA Polymerase Detachment

A

RNA polymerase dissociates from the DNA after transcribing the terminator sequence, releasing the newly synthesized RNA molecule.

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7
Q

In bacteria ___ is favored over ___

A

Efficiency, complexity

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8
Q

Many genes are ____

A

Constitutive - always on

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9
Q

The basic transcriptional control system is the

A

Operon - a cluster of genes on a DNA strand that are transcribed together as a single unit

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10
Q

Operon regulation (Prokaryotes)

A

regulated by single on/off switches for transcription

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11
Q

Polycistronic mRNA

A

The genes within an operon are transcribed as a single polycistronic mRNA (one long RNA molecule) that contains the coding information for multiple genes (or ORFs - Open Reading Frames).

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12
Q

Promoter

A

The DNA region where sigma factor (σ) and RNA polymerase bind to initiate transcription.

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13
Q

Operator

A

binding site. Operators regulate the transcription of nearby genes by controlling whether RNA polymerase can access the promoter region to start transcription

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14
Q

IRES (Internal Ribosome Entry Sites)

A

Sequences in the mRNA that allow ribosomes to bind at multiple sites, enabling translation of several proteins from one mRNA molecule.

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15
Q

Inducible Operon

A

An operon that is normally off but can be turned on by an inducer molecule (e.g., the lac operon for lactose metabolism).

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16
Q

Repressible Operon

A

An operon that is usually on but can be turned off by a corepressor molecule (e.g., the trp operon for tryptophan synthesis).

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17
Q

Lac Operon

A

An inducible operon involved in lactose metabolism. It is turned on when lactose (or allolactose) is present and inactivates the repressor.

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18
Q

Trp Operon

A

A repressible operon involved in tryptophan biosynthesis. usually on. It is turned off when tryptophan (the corepressor) is abundant.

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19
Q

Repressor

A

A protein that binds to the operator of an operon to block transcription by preventing RNA polymerase from transcribing the operon.

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20
Q

Singletons

A

Genes in bacteria that are regulated individually, not grouped into operons.

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21
Q

Lac Operon

A

An inducible operon that is usually off, but can be turned on in the presence of lactose.

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22
Q

Lactose

A

A milk sugar (glucose + galactose) that bacteria metabolize.

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23
Q

β-galactosidase (lactase)

A

Enzyme encoded by lacZ that cleaves lactose into galactose and glucose.

24
Q

Permease

A

Enzyme encoded by lacY that transports lactose into the bacterial cell.

25
Q

Galactoside Acetyltransferase (GAT)

A

Enzyme encoded by lacA that is involved in modifying galactosides (role is less understood).

26
Q

Promoter

A

The DNA sequence where RNA polymerase binds to initiate transcription of the lac operon genes.

27
Q

Operator

A

The region near the promoter where the lac repressor binds to block transcription in the absence of lactose.

28
Q

Lac Repressor (lacI)

A

A protein encoded by the lacI gene that binds to the operator to prevent transcription of the lac operon in the absence of lactose.

29
Q

Inducer (Allolactose)

A

The molecule that inactivates the lac repressor when lactose is present. Allolactose, a form of lactose, binds to the repressor, causing it to detach from the operator.

30
Q

Lac Operon Activation

A

When allolactose binds to the repressor, it removes the repressor from the operator, allowing RNA polymerase to transcribe the lacZYA genes.

31
Q

LacI Gene

A

Encodes the lac repressor. It is not part of the lac operon but regulates the operon by binding to the operator to prevent transcription.

32
Q

Lac Operon and Glucose

A

The lac operon is regulated by glucose levels. High glucose = lac operon off, low glucose = lac operon on.

33
Q

cAMP

A

Cyclic AMP (cAMP) is a signaling molecule whose levels are inversely proportional to glucose levels.

33
Q

cAMP and CRP Complex

A

When glucose is low, high cAMP binds to CRP (cAMP receptor protein), forming a complex that binds to the lac promoter to enhance RNA polymerase binding.

34
Q

CRP Binding

A

CRP-cAMP complex binds to the lac promoter and aids the recruitment of RNA polymerase to increase transcription of the lac operon genes.

35
Q

Effect of High Glucose on cAMP

A

High glucose = low cAMP, which means CRP cannot bind to the lac promoter, resulting in low transcription of the lac operon (even if lactose is present).

36
Q

Low Glucose and Lac Operon Activation

A

Low glucose = high cAMP → CRP-cAMP complex binds to the lac promoter, promoting transcription of the lac operon.

37
Q

Glucose Override System

A

The “glucose override” ensures that bacteria use glucose preferentially. When glucose is high, the lac operon is off, even if lactose is present.

38
Q

Transcription of LacZYA

A

Transcription of lac operon genes (lacZYA) is promoted when glucose is low (cAMP is high) and inhibited when glucose is high (cAMP is low).

39
Q

low glucose

A

high cAMP

40
Q

High glucose

A

low cAMP

41
Q

Tryptophan

A

One of the 20 amino acids. Bacteria synthesize tryptophan, but humans must obtain it from food.

41
Q

Key Genes in Trp Operon

A

trpE, trpD, trpC, trpB, trpA – genes that encode the enzymes for tryptophan synthesis.

42
Q

Polycistronic mRNA

A

The genes trpE, trpD, trpC, trpB, trpA are transcribed together into one long polycistronic mRNA (trpEDCBA).

43
Q

Trp Repressor (trpR)

A

Encoded by the trpR gene (outside the operon), the trp repressor prevents transcription of the operon when tryptophan is present.

44
Q

Trp Repressor Mechanism

A

When tryptophan is present, it binds to the trp repressor, activating it and allowing it to bind to the operator, blocking transcription of the operon.

45
Q

Repression of Trp Operon

A

High tryptophan levels activate the trp repressor, which binds to the operator and blocks transcription, saving energy and resources.

46
Q

When Trp is Low

A

When tryptophan is low, the trp repressor is inactive, allowing the operon to be on and transcription to occur for tryptophan production.

47
Q

Repressible vs. Inducible Operons

A

The trp operon is repressible (usually on, turned off when enough tryptophan is made), while the lac operon is inducible (usually off, turned on when lactose is present).

48
Q

Attenuation in Trp Operon

A

Attenuation regulates transcription after it has started, in response to tRNA^Trp levels. It can abort transcription midway through.

49
Q

TrpL Leader Sequence

A

The trpL leader sequence is a 130 bp region upstream of the trpEDCBA genes that contains an attenuator sequence capable of forming a hairpin structure.

50
Q

TrpL Peptide

A

The trpL leader sequence encodes a short peptide of 14 amino acids, including two adjacent tryptophans, which are rare and crucial for attenuation regulation.

51
Q

Transcription and Translation Coupling

A

In bacteria, transcription and translation are coupled. The ribosome begins translating the mRNA as it is transcribed.

52
Q

Attenuation Mechanism

A

Low tRNA^Trp causes the ribosome to stall at tryptophan codons in the trpL sequence, preventing hairpin formation and allowing transcription to continue.

53
Q

Effect of High tRNA^Trp

A

High tRNA^Trp allows the ribosome to pass over the tryptophan codons in trpL, enabling the formation of the hairpin terminator, halting transcription.

54
Q

Trp Operon Attenuation vs. TrpR Repression

A

TrpR repression blocks transcription initiation based on tryptophan levels, while attenuation aborts transcription midway based on tRNA^Trp levels.

55
Q

When Attenuation Causes Transcription to Stop

A

High tRNA^Trp → ribosome moves past codons → hairpin forms → transcription terminates early.

56
Q

When Attenuation Allows Transcription to Continue

A

Low tRNA^Trp → ribosome stalls → hairpin does not form → transcription proceeds to trpEDCBA genes.

Genetics EXAM 3 (4 decks)

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