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BioChem 2 > Gene Expression 1 > Flashcards

Gene Expression 1 Flashcards

1
Q

What is gene expression?

A

The process that result in the production of functional protein

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2
Q

What controls gene expression?

A 
Levels of transcription
processing (splicing in eukaryotes)
translation
mRNA stability
Protein stability
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3
Q

What is a transcription factor?

A

Proteins that bind to DNA and affect the transcription of genes located near where they bind

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4
Q

Why is gene expression control important?

A

Allows for organisms to be able to respond their their environment. For example, e coli prefers glucose, but must be able to use other sugars when they’re available.

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5
Q

What is an operon?

A

A prokaryotic system for organizing genes with related functions under the same transcriptional control.

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6
Q

What do genes on the same operon in prokaryotes do?

A

They are all synthesized on the same mRNA.

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7
Q

What does polycistronic mean?

A

mRNA’s containing multiple gene coding sequences

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8
Q

Describe the lactose operon

A

Consists of three linked structural genes that encode enzymes of lactose utilization, plus adjacent trajectory sites

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9
Q

What are the three enzymes of lactose operon?

A

–z, y and a– encode for beta-galactosidase, beta-galactoside permase and thiogalactoside transacetylase

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10
Q

Where does transcription of the lac operon commence near?

A

A promoter (lacP) before lacZ, and it transcribes a 5200 nucletoide mRNA, ending at a terminator beyond lacA.

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11
Q

What does regulation of the lac operon involve?

A

Three regions of DNA near the transcriptional start site. Move in the 5’ to 3’ direction, the CAP binding site, promoter, operator.

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12
Q

How is negative transcriptional regulation accomplished?

A

Through a protein known as the lac repressor.

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13
Q

What does the lac repressor do?

A

binds to the operator region, overlaps with the promoter and inhibits binding of RNA polymerase.

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14
Q

What does an inducer molecule do?

A

It binds to the lac repressor and changes its shape to reduce its ability to bind the operator, thus allows RNA polymerase to bind the promoter and start transcription.

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15
Q

What is the inducer molecule?

A

It is related to lactose and is known as allo-lactose. Only made when lactose is present.

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16
Q

What happens when the inducer molecule is not present?

A

The lac repressor binds tightly to the operator and inhibits transcription of the operon

17
Q

What protein acts positively to help activate the lac operon?

A

CAP (also called CRP)

18
Q

What does CAP do?

A

Binds to cAMP and causes a shape change in CAP that allows it to bind to the CAP binding site. This stimulates binding of RNA polymerase and transcription of the operon.

19
Q

What regulates the trp operon of E Coli?

A

Transcription factors and by the phenomenon of attenuation

20
Q

What does the trp repressor do?

A

bind to the trp operator sequence and inhibit transcription of the operon. ONLY CAN HAPPEN WHEN IT IS BOUND TO TRYPTOPHAN

21
Q

What is attenuation

A

Regulatory mechanism for several E. coli operons.

22
Q

How does attenuation occur?

A

a short leader sequence, which is a short open reading frame that contains codons for the amino acid in question

23
Q

When does translation of the trp operon begin?

A

As soon as the AUG codon for the leader sequence is transcribed.

24
Q

How many regions of mRNA for trp operon exist?

A
  1. 1 pairs with 2, 3 pairs with 4, 2 pairs with 3.
25
Q

What happens with 3 pairs with 4?

A

creates a transcriptional terminator and transcription is immediately terminated

26
Q

What happens if 2 pairs with 3?

A

Then 3 cannot pair with 4, so transcription does not immediately terminate

27
Q

What happens if tryptophan is in short supply?

A

The ribosome pauses on region 1 of the mRNA, thus preventing 1 from pairing with 2 and allows 2 to pair with 3. This means that no terminator is created and transcription continues through the operon.

28
Q

If tryptophan is abundant…

A

the ribosome moves quickly through 1 and covers region 2. Thus 2 can’t pair with 3, and 3 pairs with 4, creating termination.

29
Q

riboswitches

A

RNA structures that can form and bind a molecule.

BioChem 2 (9 decks)

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