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Biology 2 > Lecture 18 control of gene expression > Flashcards

Lecture 18 control of gene expression Flashcards

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1
Q

Why do prokaryotes only make proteins when they are needed?

A

To conserve energy and resources

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2
Q

How do prokaryotic cells shut off supply of unneeded proteins?

A
  • Downregulate the transcription of mRNA
  • Hydrolyze mRNA after it is made
  • Prevent translation of the mRNA at the ribosome
  • Hydrolyze the protein after it is made
  • Inhibit the function of the protein
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3
Q

What must a prokaryotic cell do in order to shut off supply of unneeded proteins?

A
  • Respond to the environmental signals

- Must be efficient

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4
Q

Why is transcriptional regulation preferred?

A

It is the most efficient because it conserves energy

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5
Q

What is the preferred energy source for E.coli?

A

Glucose

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6
Q

What is lactose?

A

B-Galactoside: galactose-B linked to glucose

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7
Q

What three proteins are needed for E.coli to take up and metabolize lactose?

A
  • B-galactoside permease
  • B-galactosidase
  • B-galactoside transacetylase
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8
Q

How are the three genes for lactose uptake situated in relation to each other?

A

The three genes for lactose uptake and metabolism

are adjacent on the chromosome

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9
Q

How are the three genes for lactose uptake/metabolism linked?

A

The three genes share one promoter and are

transcribed together

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10
Q

What is an operon?

A

Operon: unit comprising two or more structural genes,

one promoter and one operator.

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11
Q

What is the lac operon?

A

The lac operon contains the genes for lactose metabolism

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12
Q

What are structural genes?

A

Structural genes encode protein or RNA products which

are not regulatory factors.

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13
Q

What is an operator?

A

Operator: stretch of DNA which binds regulatory proteins.

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14
Q

What is a repressor protein?

A

Repressor protein binds to the operator and

prevents transcription.

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15
Q

What is the name of the operon containing the genes for the three lactose-metabolizing E.coli genes?

A

The lac operon

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16
Q

What are the two binding sites on the repressor protein?

A

One for the operator and one for the inducers

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17
Q

What are the inducers for the lac operon?

A

Molecules of lactose

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18
Q

How does binding with the inducer effect the repressor?

A

changes the shape of the repressor protein by allosteric modification, prevents the repressor binding to the operon

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19
Q

What happens when the concentration of lactose drops?

A

The inducer molecules (lactose) separate from the repressor, the repressor returns to its original shape and binds to the operator.

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20
Q

Why does translation stop after the transcription of the lac operon stops?

A

Because the mRNA that is already present breaks down quickly

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21
Q

What is the name of the type of system in which the inducer regulates binding of the repressor?

A

An inducible system

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22
Q

What encodes for repressor genes?

A

Regulatory genes

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23
Q

What is the regulatory gene that codes for the repressor of the lac operon called?

A

i (inducibility) gene

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24
Q

Where is i in relation to the operon it regulates?

A

Close, however, some regulatory genes are distant from their operons

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25
Q

What is the promoter of the i gene called?

A

pi (the i is subscript)

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26
Q

How is the amount of repressor protein controlled?

A

The promoter’s gene, pi, does not bind to RNA polymerase effectively, only enough to synthesize 10 repressor molecules per generation

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27
Q

What is the name given to the type of gene of the repressor for the lac operon?

A

Constitutive- it is made at a constant rate (there is no operator between pi and i gene
No environmental control

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28
Q

Operator- repressor control ______ transcription in the lac operon.

A

Induces

29
Q

Operator-repressor control ________ transcription in the trp operon

A

Represses

30
Q

Why does E.coli switch of the enzymes for the amino acid tryptophan?

A

When it is present in ample concentrations, it is advantageous to switch off this gene

31
Q

What does it mean for a protein to be repressible?

A

It can be turned off in response to biochemical cues

32
Q

How does a repressor protein shut off its operon in repressible systems?

A

It first binds to a corepressor

33
Q

Where does a corepressor come from?

A

It is either the end product itself (trytophan) or an analog of it

34
Q

What do inducible systems generally control?

A

Catabolic pathways

35
Q

What do repressible systems generally control?

A

Anabolic pathways

36
Q

How else can protein synthesis be controlled?

A

By increasing promoter efficiency

37
Q

What is the series of steps in the lac operon for the promotor to bind RNA polymerase?

A

Regulatory protein CRP binds to nucleoside adenosine 3’,5’-cyclic monophosphate (cyclic AMP, cAMP).
CRP-cAMP complex binds to DNA upstream of the promotor

38
Q

What is the result of CRP-cAMP complex binding upstream of the DNA promotor?

A

More efficient binding of RNA polymerase to the promoter and thus elevated levels of transcription of structural genes

39
Q

What happens when there is high glucose and lactose present?

A

High glucose leads to low levels of cAMP, so CRP does not undergo conformational change and therefore RNA polymerase is not asissted in binding to promoter

40
Q

What is it called when a preferred energy source represses other catabolic pathways?

A

Catabolite repression

41
Q

What is the inducible lac operon and repressible trp operon examples of?

A

negative control of transcription.

42
Q

What is negative control of transcription?

A

a repressor prevents transcription

43
Q

What is positive control of transcription?

A

an activator increases transcription

44
Q

What is an example of positive control?

A

The cAMP-CRP control of the lac operon

45
Q

What are the boundaries between introns and exons called?

A

Consensus sequneces

46
Q

What are consensus sequences?

A

Short stretches of DNA that appear with little variation in many genes

47
Q

How is gene expression regulation different to DNA replication regulation?

A

In DNA replication, it is all or nothing,

In gene expression, it is highly selective

48
Q

What are the two types of regulation that are responsible for differences in proteins among cell types?

A

Transcriptional regulation

Posttranscriptional regulation

49
Q

How can transcriptional regulation and posttranscriptional regulation be distinguished?

A

By examining the actual mRNA sequences made within the nucleus of each cell type

50
Q

What are housekeeping genes?

A

Those that encode for proteins involved in basic metabolic processes that occur in every living cell

51
Q

How is the structure of genes in eukaryotes and prokaryotes different?

A

Prokaryotes have functionally related genes grouped into operons
Eukaryotes have solitary genes

52
Q

How are several eukaryotic genes expressed at once?

A

Common control elements in each of the genes allow all of the genes to respond to the same signal

53
Q

How are DNA polymerases different in prokaryotes and eukaryotes?

A

Prokaryotes have just one

Eukaryotes have 3

54
Q

Which RNA polymerase catalyzes the transcribes protein-coding genes in eukaryotes?

A

RNA polymerase II

55
Q

How can eukaryotes regulate the rate of their transciption?

A

Additional sequences in their genes

56
Q

What are the two sequences of a prokaryotic promoter?

A

Recognition sequence- recognised by RNA polymerase

TATA box- where DNA begins to dentature so the template strands can be exposed.

57
Q

What must assemble on the chromosome before eukaryotic RNA polymerase can bind to the promoter?

A

Transcription factors

58
Q

What is the first step in eukaryotic transcription factors assembling on a chromosome?

A

The protein TFIID binds to the TATA box

59
Q

What happens when TFIID binds to the TATA box?

A

It changes the shape of TFIID and the DNA, presenting a surface that attracts other transcription factors to form a transcription complex.

60
Q

What are specific promoters important in?

A

Differentiation (specialization of cells during development)

61
Q

Where are regulator sequences found in eukaryotic cells?

A

Upstream of the promoter

62
Q

What binds to the regulator sequence?

A

Regulator proteins (such as beta-globin gene) bind to these sequences- these bind to adjacent transcription complexes and activate it

63
Q

What does TFIIH do?

A

denatures DNA

64
Q

What does TFIIB do?

A

helps identify the initiation site

65
Q

What does TFIIF do?

A

helps recruit RNA polymerase

66
Q

What does TFIIE do?

A

helps stabilise denatured DNA

67
Q

What is an enhancer sequence?

A

A regulatory sequence which binds activator proteins to activate transcription or increases rate of transcription.

68
Q

What is a silencer sequence?

A

regulatory sequence which binds factors that repress transcription.

69
Q

What is the purpose of bending the DNA?

A

To bring distant regulatory sequences, and their associated proteins, into contact

Biology 2 (14 decks)

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