The Lac Operon (5.1.1)

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What does E.coli respire?
It usually respires glucose, but it can also respire lactose when it's available.
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What are the two enzymes needed for the absorption and digestion of lactose?
Lactose permease- enables the bacterial cell to take up lactose. Beta galactosidase- used to break down the lactose into monosaccharides for respiration.
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What does it mean that these enzymes are inducible?
They are produced at varying rates according to the cell's circumstances and are only made when lactose is present. The presence of lactose is the trigger for the enzymes to be made.
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What is an operon?
An operon is a stretch of DNA made up of structural genes and control sites.
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What are Z and Y?
The structural genes.
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What enzyme does Z code for the production of?
Beta galactosidase.
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What enzyme does Y code for the production of?
Lactose permease.
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What is O?
The operator region. It's a length of DNA next to the structural genes- it can switch them on and off.
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What is P?
The promoter region. It's a length of DNA to which the enzyme RNA polymerase attaches in order for the genes Y & Z to be transcribed.
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What is I?
The regulator gene. It is not part of the operon- it's found some distance away from it. It codes for a repressor protein- this has two binding sites on it and can either attach to the operator gene or lactose if it's present.
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What happens when lactose is absent?
Repressor protein attaches to O region of operon. This blocks part of P section too, so RNA polymerase can't attach. This means structural genes Z & Y can't be transcribed. No protein synthesis can occur- the enzymes are not made.
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What happens when lactose is present?
Lactose attaches to binding site on repressor protein, changing its shape slightly so it can't fit into binding site on O region. This leaves P site exposed, & RNA polymerase can now attach and trigger transcription of Y & Z genes. Enzymes now made.
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Other cards in this set

Card 2

Front

What are the two enzymes needed for the absorption and digestion of lactose?

Back

Lactose permease- enables the bacterial cell to take up lactose. Beta galactosidase- used to break down the lactose into monosaccharides for respiration.

Card 3

Front

What does it mean that these enzymes are inducible?

Back

Preview of the front of card 3

Card 4

Front

What is an operon?

Back

Preview of the front of card 4

Card 5

Front

What are Z and Y?

Back

Preview of the front of card 5
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