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Genetics > Chapter 14 > Flashcards

Chapter 14 Flashcards

1
Q

What is gene regulation

A

The level of gene expression can vary under different conditions

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2
Q

What are constitutive genes

A

Genes that are unregulated and have a constant level of expression

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3
Q

What is the benefit of gene regulation

A

It encodes proteins only when they are required

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4
Q

How is gene expression regulated during transcription

A

Genetic regulatory proteins bind to dna and control rate of transcription
Transcription stops soon after beginning due to formation of transcriptional terminator

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5
Q

What three things can stop translation from starting

A

Translational repressor proteins can bind to mRNA
Riboswitches can produce mRNA confirmation
Antisense RNA can bind to mRNA

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6
Q

When else can regulation occur of gene expression in bacteria

A

When a protein undergoes post translational changes to make it a functional protein

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7
Q

What does transcriptional regulation involve

A

Repressors which bind to DNA and inhibit transcription
Activators which bind to DNA and increase transcription

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8
Q

What is negative and positive control in regards to regulation

A

Negative is transcriptional regulation by repressor proteins and positive control is regulation by activator proteins

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9
Q

How do effector molecules affect transcription

A

They bind to regulatory proteins but not the dna directly
Also known as inducers because they can bind activators and repressors and either prevent them or cause them to bind to DNA
These genes are termed inducible

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10
Q

What do corepressors and inhibitors do for transcription

A

Corepressors bind to repressors and cause effector molecules to bind to DNA
Inhibitors bind to activators and prevent effector molecules from binding
These genes are termed repressible

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11
Q

When there is an inducer present what happens

A

It causes a conformational change that inhibits the ability of the repressor protein to bind to DNA and transcription proceeds

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12
Q

What happens when an inducer is bound to an activator protein

A

It enables the activator protein to bind to the DNA and activate transcription

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13
Q

What happens when a corepressor is bound to the repressor protein

A

Conformational change occurs that allows the repressor to bind to DNA and inhibit transcription

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14
Q

What happens when an inhibitor is present

A

Causes a conformational change that inhibits the ability of the activator protein to bind to the DNA which inhibits transcription

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15
Q

What is enzyme adaptation

A

Enzyme appears in the cell only after the cell has been exposed to the enzymes substrate

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16
Q

What is an operon

A

Region of DNA that involves sequences that aren’t structural or expressed parts of the DNA
Consists of a few structural genes under control of one promoter

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17
Q

What is a polycistronic mRNA

A

Contains coding sequence for two or more structural genes
This allows bacterium to regulate a group of genes that encode proteins with a common functional goal

18
Q

What DNA sequences operons contain

A

Promoter, terminator, structural genes, operator

19
Q

What does the lac operon and lacI gene do

A

Lac operon controls lactose metabolism
LacI gene is important for regulating the operon

20
Q

Are are the elements of a lac operon

A

Promoter which binds RNA polymerase
Operator which binds the lac repressor protein
Cap sit which binds the cap

21
Q

What are the structural genes of the lac operon

A

LacZ which encodes beta galactosidase
LacY which encodes the lactose permease
LacA which encodes galactoside transacetylase

22
Q

What are some characteristics of the lacI gene

A

Not part of lacrosse operon
Has its own promoter
Expressed at low levels and encodes the lac repressor

23
Q

What two things regulate the lac operon

A

Repressor protein
Activator protein

24
Q

What happens in the absence of inducer allolactose

A

The repressor protein is tightly bound to operator site and inhibits the ability of the rna polymerase to transcribe the operon

25
Q

What happens when allolactose is available

A

Binds to receptor and changes confirmation of repressor protein which prevents it from binding to operator site so RNA polymerase can transcribe the operon

26
Q

What happens when lactose becomes available

A

A small amount is converted to allolactose by beta galactosidase and the allolactose binds to the repressor and causes it to fall off operator site
Then lac operon proteins are synthesized which promotes efficient uptake and metabolism of lactose until lactose is depleted and allolactose levels decrease

27
Q

What is catabolite regression

A

When exposed to both lactose and glucose the E. coli uses the glucose first so catabolite regression prevents the use of lactose

28
Q

What is diauxic growth

A

The sequential use of two sugars by a bacterium

29
Q

What is cyclic amp

A

Produced from atp via adenylyl Cyclase
Binds to CAP

30
Q

What is the camp-CAP complex an example of

A

Transcriptional regulation that is inducible and under positive control

31
Q

How is the camp-CAP complex related to the lac operon

A

It binds to the CAP site near the lac promoter and increases transcription
When glucose is present adenylyl Cyclase is inhibited which decreases levels of camp so it can’t bind to CAP and transcription rate decreases

32
Q

What are the three operator sites in the lac operon

A

O1 which is next to the promoter
O2 which is downstream in the lacZ coding region
O3 which is slightly upstream of the promoter

33
Q

What must the lac repressor do to cause repression

A

Must bind to two of the three operators
Can be O1 and O2 or O1 and O3 but not O2 and 3

34
Q

What is the significance of the lac repressor binding to the two operator sites

A

The dna forms a loop which brings the operator sites closer together

35
Q

What does trpL and trpR do

A

TrpR encodes the trp repressor proteins and functions in repressing
TrpL encodes a short leader peptide and functions in attenuation

36
Q

What happens when tryptophan levels are low

A

Tryptophan doesn’t bind to trp repressor protein which prevents repressor protein from binding to operator site

37
Q

What happens when tryptophan levels are too high

A

Tryptophan acts as a corepressor that binds to trp repressor protein and tryptophan-trp repressor complex then binds to the operator site to inhibit transcription

38
Q

What happens when attenuation occurs

A

RNA is transcribed only to attenuator sequence and then transcription is terminated

39
Q

When does attenuation occur

A

In bacteria because transcription and translation are coupled
Transcription will terminate before the entire mRNA is made which is facilitated by an attenuator

40
Q

Why are two tryptophan codons found in the mRNA from the trpL gene important

A

It’s a way for bacterium to sense tryptophan levels
mRNA from trpL can form stem loops

Genetics (14 decks)

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