16.3.1 Gene control - Lac operon (part of inheritance) Flashcards

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1
Q

The nucleus of every cell in the human body contains the same ..?

A

genes

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2
Q

What is not expressed in every cell?

A

every gene
- Not all of these genes are expressed all the time

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3
Q

There are several mechanisms that exist within cells to make sure the correct genes are expressed in the correct cell at the right time.
What do they involve?

A

regulatory genes

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4
Q

What is a structural gene?

A

codes for a protein that has a function within a cell
For example, the F8 gene codes for the protein Factor VIII involved in blood clotting

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5
Q

What is a regulatory gene?

A

codes for a protein that helps to control the expression of another gene

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6
Q

Structural and regulatory genes that work together are usually found..?

A

close together

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7
Q

When are inducible enzymes only synthesized?

A

when their substrate is present

The presence of the substrate induces the synthesis of of the enzyme by causing the transcription of the gene for the enzyme to start

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8
Q

repressible enzymes synthesized as normal. Until?

A

repressor protein binds to an operator

The presence of the repressor protein represses the synthesis of the enzyme by causing the transcription of the gene for the enzyme to stop

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9
Q

Why can controlling synthesis of enzymes be beneficial for cells?

A

as it stops materials and energy being wasted

For example, using materials and energy to synthesize an enzyme when its substrate is not present and it can’t carry out its function would be highly wasteful

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10
Q

What do regulatory genes control?

A
  • control structural genes and their levels of protein production
  • sometimes have control over several structural genes at once
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11
Q

What do regulatory genes control?

A
  • control structural genes and their levels of protein production
  • sometimes have control over several structural genes at once
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12
Q

What can structural genes in prokaryotes form?

A

an operon

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13
Q

What is an operon?

A

a group or a cluster of genes that are controlled by the same promoter

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14
Q

Which operon is found in some bacteria which is the most well known?

A

lac operon

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15
Q

what does the lac operon control the production of?

A

the enzyme lactase (also called β-galactosidase) and two other structural proteins

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16
Q

What does lactase break down?

A

the substrate lactose so that it can be used as an energy source in the bacterial cell

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17
Q

What type of enzyme is lactase?

A

inducible enzyme that is only synthesized when lactose is present

This helps prevent the bacteria from wasting energy and materials

18
Q

Structure of the lac operon
The components of the lac operon are found in the following order:

A
  • Promoter (for structural genes)
  • Operator
  • lac Z
  • lac Y
  • lac A
19
Q

What is a promoter?

A

A region of DNA required to allow transcription of a gene to take place

20
Q

what does structural gene lacZ code for?

A

lactase

21
Q

What does structural gene lacY code for?

A

permease (allows lactose into cell)

22
Q

What does structural gene lacA code for?

A

transacetylase

trans-acet-y-lase

23
Q

Located to the left (upstream) of the lac operon on the bacterium’s DNA there is also the:

A

Promoter for regulatory gene
Regulatory gene lacI that codes for the lac repressor protein

24
Q

How many binding sites does the lac repressor protein have?

A
  • 2 binding sites that allow it to bind to the operator in the lac operon and also to lactose (the effector molecule)
25
Q

When the lac repressor protein binds to the operator:
describe events

A

it prevents the transcription of the structural genes as RNA polymerase cannot attach to the promoter

26
Q

When the lac repressor protein bind to lactose:
describe event

A

the shape of the repressor protein distorts and it can no longer bind to the operator

27
Q

When lactose is absent
The following processes take place when lactose is absent in the medium that the bacterium is growing in:

A
  • The regulatory gene is transcribed and translated to produce lac repressor protein
  • The lac repressor protein binds to the operator region upstream of lacZ
  • Due to the presence of the repressor protein RNA polymerase is unable to bind to the promoter region
  • Transcription of the structural genes does not take place
  • No lactase enzyme is synthesized
28
Q

When lactose is present
The following processes take place when lactose is present in the medium that the bacterium is growing in:

A
  • There is an uptake of lactose by the bacterium
  • The lactose binds to the second binding site on the repressor protein, distorting its shape so that it cannot bind to the operator site
  • RNA polymerase is then able to bind to the promoter region and transcription takes place
  • The mRNA from all three structural genes is translated
    -Enzyme lactase is produced and lactose can be broken down and used for energy by the bacterium
29
Q

What do prokaryotes use to control the expression of genes in cells?

A

operons

30
Q

What do Eukaryotes use to control gene expression?

A

transcription factors

31
Q

What is a transcription factor?

A

is a protein that controls the transcription of genes by binding to a specific region of DNA

32
Q

What do transcription factors insure?

A

They ensure that genes are being expressed in the correct cells, at the correct time and to the right level

33
Q

What do transcription factors allow organisms allow organisms to respond to?

A

their environment

34
Q

How transcription factors work

A

Some transcription factors bind to the promoter region of a gene

This binding can either allow or prevent the transcription of the gene from taking place

35
Q

the presence of a transcription factor will either..?

A

increase or decrease the rate of transcription of a gene

For example, PIF is a transcription factor found in plants that activates the transcription of the amylase gene

36
Q

What do plant cells use in a similar way to animal cells?

A

transcription factors

37
Q

What is Gibberellin?

A
  • a hormone found in plants (eg wheat and barley) that controls seed germination by stimulation the synthesis of the enzyme amylase
38
Q

How does giberellin control seed germination by stimulating the synthesis of the enzyme amylase?

A

It does this by influencing transcription of the amylase gene

When gibberellin is applied to a germinating seed there is an increased amount of the mRNA for amylase present

39
Q

What is necessary for the synthesis of amylase?

A

the breakdown of DELLA protein by gibberellin

40
Q

The process of the breakdown of DELLA protein by gibberellin

A
  • DELLA protein is bound to PIF, preventing it from binding to the promoter of the amylase gene so no transcription can occur
  • Gibberellin binds to a gibberellin receptor and enzyme which starts the breakdown of DELLA
  • PIF is no longer bound to DELLA protein and so it binds to the promoter of the amylase gene
  • Transcription of amylase gene begins
    -Amylase is produced