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Genetics > Control of gene expression > Flashcards

Control of gene expression Flashcards

Bacterial gene expression, lac operon, eukaryotic gene expression, initiation of transcription and chromatin structure.

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Biology 101 flashcards
1
Q

The level of RNA doesn’t always equal the amount of…

A

protein.

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2
Q

What are differences in cells and tissues due to?

A

Which genes in the genome are expressed at which time (because all cells in complex multicellular organisms contain the same DNA).

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3
Q

Give 2 important reasons as to why the control of gene expression matters.

A

Life cycle related changes of an organism.

Response to changes in environmental conditions.

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4
Q

Why is transcription and translation coupled in bacteria (takes place simultaneously in the cytoplasm)?

A

They have no nuclear membrane, one cytoplasmic compartment and no histones.

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5
Q

How is translation initiated in prokaryotes?

A

A promoter is required for RNA polymerase to bind (also in eukaryotes).
Sigma factor (a subunit of RNA polymerase binds).
Additional control sequences can determine when a gene is transcribed.

Promoter = indicates correct starting point for transcription.

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6
Q

When does control of gene expression occur?

A

In transcription and translation.

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7
Q

What do sequences in the DNA signal to?

A

sigma factor/RNA polymerase

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8
Q

What determines which DNA strand is transcribed?

A

polarity of promoter orients RNA polymerase and determines which DNA strand is transcribed

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9
Q

What signals to RNA polymerase to terminate transcription?

A

Sequences in DNA.

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10
Q

Regions transcribed into RNA contain nucleotide sequences of the terminator but not the…

A

promoter.

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11
Q

What is an operon?

A

A cluster of genes in prokaryotes with a related function.

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12
Q

How many promoters does an operon have?

A

One.

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13
Q

How are the genes in an operon transcribed?

A

All together.

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14
Q

How is all the mRNA translated?

A

To give separate proteins.

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15
Q

For the E.coli lac operon, list the 3 genes after the promoter.

A

lacZ, lacY, lacA

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16
Q

What is mRNA translated to?

A

beta galactosidase, beta galactoside permease and beta galactoside transacetylase

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17
Q

What do the proteins work together on?

A

Glucose metabolism.

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18
Q

What are polycistronic transcripts?

A

Produce multiple proteins from one mRNA.

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19
Q

In lac operon’s default state, why is it switched off?

A

Lactose is absent from the environment and the regulatory gene lacI produces an active repressor.

Negative control (operons are switched off by active form of repressor).

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20
Q

What happens in an environment when lactose is present and it enters the cell?

A

It binds to repressor causing it to be inactivated so it cannot interact with lac operon.
RNA polymerase transcribes lacZ, lacY and lacA genes.
Lactose is metabolised.

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21
Q

What does it mean to say operon is inducible?

A

It is activated in response to a stimulus (lactose).

22
Q

When glucose and lactose are both present in the environment, what does E.coli use? Why?

A

Enzymes for glucose breakdown in glycolysis are continually present.

23
Q

When does E.coli use lactose?

A

As an energy source when lactose is present and glucose is in short supply.

24
Q

What does E.coli need to do when using lactose?

A

Synthesise appreciable quantities of enzymes for lactose breakdown.

25
Q

What happens when glucose is scarce?

A

CAMP present in absence of glucose.
CAP (catabolite activator protein) is activated by binding with CAMP (cyclic AMP).
Activated CAP attaches to promoter of lac operon and increases affinity of RNA polymerase.
Transcription is accelerated.
(Positive control of genes).

26
Q

When is eukaryotic gene expression controlled?

A

At several points in the central dogma:
1. transcriptional control
2. RNA processing control
3. mRNA transport and localisation control
4. mRNA degradation control
5. translational control
6. protein degradation control
7. protein activity control

27
Q

What is the role of RNA polymerase I?

A

Transcribes most rRNA genes.

28
Q

What is the role of RNA polymerase II?

A

Transcribes all protein-coding genes, miRNA genes, genes for other noncoding RNAs e.g. those of spliceosome.

29
Q

What is the role of RNA polymerase III?

A

Transcribes tRNA genes, 5S rRNA gene and genes for many other small RNAs.

5S ribosomal RNA (5S rRNA) = component of the ribosome, specifically found in the large subunit in both prokaryotic and eukaryotic cells.

30
Q

Why is Amanita Phalloides poisonous?

A

alpha amanitin inhibits RNA polymerase II

31
Q

How is transcription initiated in eukaryotes?

A

Promoter (contains sequences to promote binding of general transcription) required for RNA polymerase to bind.

RNA polymerase interacts with other proteins = general transcription factors.

Additional control sequences can determine when a gene is transcribed. Enhancer (cis-regulatory module) = eukaryotic activator protein binds to it and general transcription factors, mediator and RNA polymerase.

General transcription factor TFIIH prises apart DNA and phosphorylates RNA polymerase and releases it from most of general transcription factors to allow transcription to start.

32
Q

Activator proteins bound to regulatory DNA sequences are not sufficient to activate transcription…

A

efficiently.

33
Q

A single transcription factor can coordinate the expression of many different genes. Give an example.

A

Cortisol activated genes.

34
Q

When is the cortisol receptor activated?

A

Only in the presence of cortisol.

35
Q

What is the effect of adding an additional transcription regulator?

Look at PowerPoint if unsure.

A

Activator protein binds to activated cortisol receptor = cortisol-receptor complex.

Complex binds to the same regulatory DNA sequence in each gene.

A combination of transcription regulators is required for efficient initiation of transcription.
All three genes are now switched on as a set.

36
Q

Many cell types are generated during development by combinations of a few…

A

transcription regulators.

37
Q

Why isn’t master transcription regulator A made?

A

It’s normally required for the transcription of its own gene.

38
Q

What turns on the expression of gene A?

A

Transient (lasting only for a short time) signal.

39
Q

How else are transcription factors altered?

A

Covalent modification of DNA e.g. methylation.

40
Q

Where does methylation occur in vertebrates (diverse group of animals with a spinal column)?

A

In sequence CG (CpG site). Methyl group added to cytosine.

41
Q

What does methylated DNA do to gene expression?

A

Represses it.

42
Q

How are methylation patterns inherited?

A

Through cell division when a methylated cytosine is recognised by methyltransferase.

43
Q

How and when are the vast majority of methyl groups removed?

A

A wave of destruction after fertilisation.

44
Q

What is epigenetics?

A

The study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself.

(Heritable changes in gene function without a change to the DNA base sequence).

45
Q

In differentiated cells, epigenetics maintains patterns of…

A

gene repression.

46
Q

How does chromatin structure play a role in eukaryotic gene regulation?

A

Makes DNA inaccessible to transcription (if its condensed).

47
Q

What is histone acetyltransferase’s role in epigenetics?

A

Adds acetyl groups to histones which causes chromatin to be less condensed and initiates transcription.

48
Q

Apart from methylation and acetylation, what is another modification to DNA?

A

Phosphorylation

49
Q

Which part of core histones are covalently modified?

A

N-terminal tails (starts of proteins protruding from histone).

50
Q

What does addition of a trimethyl group (K 9) to H3 tail of histone do to functional outcome of DNA?

A

Forms heterochromatin so causes gene silencing.

51
Q

What does addition of a trimethyl group (K 4) then acetyl group (K 9) to H3 tail of histone do to functional outcome of DNA?

A

Causes gene expression.

Genetics (10 decks)

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