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Biology human perspectives 1201 > Gene regulation > Flashcards

Gene regulation Flashcards

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1
Q

Give the definition of an operon

A

An operon is a cluster of co-ordinately regulated genes, that are transcribed as a single mRNA and have a single promoter. An operon will contain genes that function in the same process. It includes structural genes (generally encoding enzymes) and regulatory sites (such as promoters and operators).

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2
Q

a lot of gene regulation occurs at the level of what?

A

transcription.

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3
Q

What is the promoter?

A

RNA polymerase binding site

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4
Q

What species has the lac operon?

A

Escherichia coli (E.coli)

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5
Q

the lac operon contains genes that encode what?

A

the lac operon contains genes that encode proteins involved in uptake and metabolism of a particular sugar, lactose.

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6
Q

Operons aren’t just made up of the coding sequences of genes. Instead, they also contain what?

A

regulatory DNA sequences

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7
Q

How do regulatory DNA sequences control transcription of the operon? Give an example.

A

These sequences are binding sites for regulatory proteins, which control how much the operon is transcribed.
E.G. The promoter, or site where RNA polymerase binds, is one example of a regulatory DNA sequence.

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8
Q

What are the two types of regulatory proteins

A

repressors & activators

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9
Q

What are activators

A

an activator binds to its DNA binding site, and increases transcription of the operon (e.g., by helping RNA polymerase bind to the promoter).

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10
Q

What are repressors

A

repressors bind to pieces of DNA called operators. When bound to its operator, a repressor reduces transcription (e.g., by blocking RNA polymerase from moving forward on the DNA).

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11
Q

The genes that encode regulatory proteins are called?

A

regulatory genes

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12
Q

Some operons are usually “off,” but can be turned “on” by a small molecule called?

A

an inducer

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13
Q

Some operons are usually “off,” but can be turned “on”. The operon is said to be called what?

A

inducible.

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14
Q

operons are usually “on,” but can be turned “off” by a small molecule. The molecule is called what?

A

a corepressor

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15
Q

operons are usually “on,” but can be turned “off” are said to be called what?

A

repressible

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16
Q

gene regulation allows bacteria to what?

A

respond to changes in their environment by altering gene expression (and thus, changing the set of proteins present in the cell).

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17
Q

If all genes were equally “active” in all cells then there would be only one what?

A

one cell type

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18
Q

What is gene “activity” ?

A

Gene activity is the level at which a gene expresses its information -usually this means production of a protein.

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19
Q

The lac operon of E. coli contains genes involved in what?

A

lactose metabolism

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20
Q

When is the lac operon expressed?

A

It’s expressed only when lactose is present and glucose is absent.

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21
Q

What regulatory protein turns the lac operon “off” ?

A

The lac repressor protein

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22
Q

Permease is encoded by the___ gene.

A

lacY gene

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23
Q

The lacY gene encodes what?

A

Permease

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24
Q

β-galactosidase is encoded by the___ gene.

A

lacZ gene

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25
Q

The lacZ gene encodes what?

A

β-galactosidase

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26
Q

E. coli should express the lac operon only when what two conditions are met?

A

Lactose is available, and

Glucose is not available

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27
Q

What three genes does The lac operon contain?

A

lacZ, lacY, and lacA

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28
Q

What is β-galactosidase and what is it responsible for?

A

It is an enzyme and it hydrolyses the disaccharide lactose into the readily usable monosaccharides glucose and galactose

29
Q

What is permease and what is it responsible for?

A

It is a membrane-embedded transport protein that helps bring lactose into the cell.

30
Q

what is RNA polymerase?

A

the enzyme that performs transcription.

31
Q

What is The operator?

A

The operator is a negative regulatory site bound by the lac repressor protein. The operator overlaps with the promoter, and when the lac repressor is bound, RNA polymerase cannot bind to the promoter and start transcription.

32
Q

What is The CAP binding site?

A

The CAP binding site is a positive regulatory site that is bound by catabolite activator protein (CAP). When CAP is bound to this site, it promotes transcription by helping RNA polymerase bind to the promoter.

33
Q

What is The lac repressor?

A

The lac repressor is a protein that represses (inhibits) transcription of the lac operon. It does this by binding to the operator, which partially overlaps with the promoter. When bound, the lac repressor gets in RNA polymerase’s way and keeps it from transcribing the operon.

34
Q

The gene that encodes the lac repressor is named….

A

lacI

35
Q

lacI gene is under control of its own p___

A

promoter

36
Q

True or False: The lacI gene happens to be found near the lac operon, but it is not a part of the operon and is expressed separately

A

True

37
Q

lacI gene is c_____ transcribed, so its protein product – the lac repressor – is always present.

A

constitutively

38
Q
  1. When lactose is not available, the lac repressor binds tightly to what?
  2. preventing what?
A
  1. the operator

2. transcription by RNA polymerase

39
Q

What happens to the lac repressor when lactose is present?

A

When lactose is available, some molecules will be converted to allolactose inside the cell. Allolactose binds to the lac repressor and makes it change conformation so it can no longer bind DNA with the operator and therefore, allowing RNA polymerase to transcribe the operon.

40
Q

What is allolactose?

A

allolactose is an isomer (rearranged version) of lactose & an inducer.

41
Q

How was gene regulation in E.coli discovered?

A

By studying mutations

42
Q

How does studying mutations lead to discoveries of the function of biological systems including gene regulation?

A

Since information flows from DNA to all levels of biology (ie. cell structure, physiology, behaviour, ecology) we can analyse the function of any biological system by analysing the effects of changes in DNA (ie. mutations).

43
Q

Name the 4 steps in the Mutational analysis of regulation of lactose utilisation genes in E. coli

A
  1. generate mutations in all genes at random then,
  2. look for bacteria that cannot use lactose (ie. cannot grow on media with lactose as the only energy source) then,
  3. check that these bacteria can grow on media using other energy sources (for example, glucose).
  4. Examine what genes are mutated in these bacteria and in what way.
44
Q

What are Cis acting factors? Give an example

A

Cis acting factors only control transcription on the same piece of DNA. The Operator is an example.

45
Q

What are Trans acting factors? Give an example

A

Trans acting factors influence transcription on other pieces of DNA. The repressor protein is an example.

46
Q

mutations in permease gene (lacY) would result in what?

A

Cannot absorb lactose

47
Q

if a bacteria cannot metabolise lactose, what does this mean

A

mutations in β-galactosidase gene (lacZ).

48
Q

What does it mean when you cannot repress (“downregulate”) lac operon transcription?

A

the lac operon becomes “constitutively” active

49
Q

Where has the mutation occurred when a bacteria cannot absorb or metabolise lactose due to no lac operon transcription?

A

mutations affecting promoter function

50
Q

Name 2 Structural mutations (e.g. affect protein structure)

A
  1. Cannot absorb lactose-(lacY).

2. Cannot metabolise lactose-(lacZ).

51
Q

Name 2 Regulatory mutations (e.g. affect gene regulation)

A
  1. mutations affecting promoter function

2. Cannot repress(“downregulate”) lac operon transcription (ie. the lac operon becomes “constitutively” active)

52
Q

What does “constitutively” active mean?

A

is when an enzyme or protein is produced in relatively constant amounts in all cells of an organism without regard to cell environmental conditions. The transcription of that enzyme/protein is constantly “on” and cannot be repressed.

53
Q

How do you spell constitutively

A

c-o-n-s-t-i-t-u-t-I-v-e-l-y-

54
Q

Repression of the lac operon requires what two things?

A
  • An active repressor protein

- A functional operator

55
Q

How can you distinguish between mutations that prevent repression?

A

By Complementation

56
Q

What is Complementation?

A

When a functional deficiency in a DNA molecule is compensated for by provision of that function from another DNA molecule

57
Q

out of the two mutations that prevent repression, which one can be Complemented?

A

Mutations in the lac I gene (repressor protein)

58
Q

What is The trp operon?

A

is a group of genes that encode biosynthetic enzymes for the amino acid tryptophan.

59
Q

The trp operon is expressed (turned “on”) when…..

A

tryptophan levels are low

60
Q

The trp operon is repressed (turned “off”) when…

A

tryptophan levels are high

61
Q

Give an example of an catabolic operon (breaking down)?

A

The lac operon

62
Q

Give an example of anabolic operon (building up)?

A

The trp operon

63
Q

What is a inducible system?

A

the cell manufactures a product only when needed

64
Q

What is a repressible system?

A

under normal conditions, the cell constantly manufactures a product, but is able to shut down manufacture when the product isn’t needed.

65
Q

The trp operon is regulated by…..

A

trp repressor

66
Q

the trp repressor blocks expression of the operon when bound to what?

A

tryptophan

67
Q

When tryptophan is around, and it attaches to the repressor molecules, what does it do to them?

A

changes their shape so they become active.

68
Q

A small molecule like trytophan, which switches a repressor into its active state, is called what?

A

a corepressor.

Biology human perspectives 1201 (1 decks)

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