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Year 2: Genetics > Lecture 13: Regulation of Gene Expression > Flashcards

Lecture 13: Regulation of Gene Expression Flashcards

1
Q

What is the central dogma of DNA?

A

DNA is transcribed to mRNA which is then translated to proteins.

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2
Q

When does translational regulation take place?

A

During the initiation stage of translation, ie. the formation of the ribosomal complex required to translate the mRNA copy of the genetic code.

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3
Q

What mediates the initiation stage of translation?

A

Translation is mediated by a complex set of translation factors; 12 transcription factors required for initiation stage.

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4
Q

What are the 12 translation factors that mediate the initiation stage of translation?

A

eIF1, eIF1A, eIF2, eIF2B, eIF3, eIF4A, eIF4B, eIF4E, eIF4G, eIF4H, eIF5, and eIF5B.

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5
Q

What is required for translation in eukaryotes?

A

Translation initiation in eukaryotes requires mRNA, amino-acyl tRNA (met), ribosome, GTP, and 12 protein initiation factors.

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6
Q

What happens during the initiation stage of translation?

A
  1. Translocation of 40S ribosome initiation complex along mRNA until AUG is identified; facilitated by translation factors complex.
  2. Release of translation factors.
  3. 60S subunit joins 40S/tRNA complex
  4. 80S ribosome-met tRNA initiation complex completed
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7
Q

Describe the regulation of the translation for the protein ferritin

A

Regulation of ferritin translation is carried out by Iron Regulatory Protein (IRP); if there are adequate iron levels, then normal translation proceeds, however, if the level of iron is abnormal the translation is regulated.
Low levels of iron levels: IRP binds to iron-response element (IRE)- interferes with translation initiation to reduce amount of ferritin produced to limit the storage of iron in an environment where there is limited freely available iron.

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8
Q

What is plasma ferritin?

A

Plasma ferritin is an indirect marker of total iron storage and is a diagnostic test for iron-deficiency anaemia, as well as being a marker for a range of pathologies.

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9
Q

What is the process by which ferritin protein translation is regulated?

A

Repressor protein (IRP) binding to 5’ untranslated sequence (IRE), blocking translation initiation.

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10
Q

What is the agent and action used to regulate ferritin protein translation?

A

Agent: Repressor proteins Action: Specific mRNAs

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11
Q

Describe the regulation of the translation for the protein Neuroguidin

A

Inhibits translation by binding to eIF4E bound to the 5’ MeG cap. Blocks formation of normal translation initiation complex as translational repressor also binds to the 3’ end, positioning the initiation complex away from 5’ end.

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12
Q

What is the agent and action used to regulate neuroguidin protein translation?

A

Agent: Repressor proteins Action: Specific mRNAs

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13
Q

What are miRNA genes?

A

MicroRNA genes code for small non-coding RNA molecules (containing about 22 nucleotides).

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14
Q

What are the importance of miRNAs?

A

MicroRNAs are critical in gene regulation. Also functions in RNA silencing and post-transcriptional regulation of gene expression.

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15
Q

What is long non-coding RNA? What is its function?

A

Long noncoding RNAs (>200 nucleotides) can form complexes with chromatin to modify structure and recruit other transcriptional-modifying factors.

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16
Q

What are the coding forms of RNA?

A
  1. mRNA: mediator of gene code from DNA to translation. DNA is transcribed to form mRNA.
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17
Q

What are the non-coding forms of RNA?

A
  1. snRNA
  2. tRNA
  3. rRNA
  4. Long non-coding RNA
  5. MicroRNA/ miRNA
18
Q

What is the function of snRNA?

A

Spliceosome component, and involved in exon splicing.

19
Q

What is the function of tRNA?

A

Translation

20
Q

What is the function of rRNA?

A

Translation, sequence recognition, and peptidyl transferase.

21
Q

What processes do miRNAs influence?

A

miRNAs influence many cell processes including cell cycle, apoptosis and cell differentiation.

22
Q

Describe the regulation of the translation by non-coding RNA

A
  1. miRNA duplex formation: Hairpin structures form in primary single stranded miRNA transcripts. Sequential cleavage by Drosha and Dicer endonucleases which yields double stranded miRNA.
  2. miRNA interacts with RISC complex and strands unwind.
  3. ss miRNA interacts with 3’ UTR of target mRNA.
  4. Translational inhibition: directly by eIF4A/translation initiation interference; indirectly by de-adenylation and increased mRNA degradation.
23
Q

What is the agent and action used for regulation by non-coding RNA?

A

Agent: micro RNAs
Action: Specific mRNAs

24
Q

How can miRNAs induce oncogenesis?

A
  1. Upregulation of oncogenic miRNA
  2. Downregulation of tumour-suppressor miRNA
  3. Mutation of target miRNA sites in tumour-promoting mRNA
25
Q

What is oncogenesis?

A

The development of

tumour(s)

26
Q

How does miRNA regulate gene expression?

A

miRNA regulates gene expression by translational repression, mRNA cleavage, and mRNA decay initiated by miRNA-guided rapid deadenylation.

27
Q

What causes downregulation of tumour-suppressor miRNA?

A

Loss of histone acetylation and aberrant DNA hypermethylation leads to loss of miRNA which are responsible for the formation of tumour suppressor proteins.

28
Q

What causes upregulation of oncogenic miRNA?

A

Loss of normal repressive epigenetic markers leads to the increase in miRNA responsible for tumour formation.

29
Q

What is an example of a tumour suppressor protein?

A

P53

30
Q

How are miRNAs and cardiovascular disease linked?

A

miRNAs and cardiovascular disease has been linked through the increase/decrease in approx. 30 circulating miRNAs. Presence/absence of these miRNAs can be used as diagnostic and prognostic markers.

31
Q

Describe the regulation of translation by phosphorylation of eIF2 and eIF2b

A
  1. Active eIF2-GTP escorts initiator Met-tRNA to ribosome. Inactive eIF2-GDP is released.
  2. Active eIF2-GTP regenerated from inactive eIF2-GDP, by action of eIF2B
    Regulation:
  3. Regulatory protein kinase enzymes phosphorylate eIF2 to eIF2B
  4. Blocks reactivation of GDP-eIF2 to GTP-eIF2 so cannot continue initiation of translation.
32
Q

What is the agent and action used to regulate translation by phosphorylation of eIF2 and eIF2b?

A

Agent: Repressor proteins (protein kinases + translation initiation factors)
Action: Global translational activity

33
Q

Describe the regulation of translation by eIF4E- binding proteins (4E-BPs).

A
  1. In the absence of growth factors, translation initiation blocked by 4E-BPs.
  2. Growth factors stimulate phosphorylation of 4E-BPs which dissociate from eIF4E and translation proceeds
34
Q

What is the agent and action used to regulate translation by eIF4E- binding proteins (4E-BPs)?

A

Agent: Repressor proteins (protein kinases + eIF binding proteins)
Action: Global translational activity

35
Q

What is the role of cell stress in translation regulation?

A

Exposure to cell stress inhibits translation via signalling pathways. Many different types of cell stress cause a global inhibition of protein synthesis via signalling cascades that lead to the reversible change in phosphorylation status of proteins involved in translation initiation.

36
Q

How is mRNA degradation controlled?

A

Rapidly degraded RNAs often contain specific AU-rich sequences near 3’ ends (AREs). AREs act as binding sites for RNA-binding proteins (RBPs) that stabilise or target mRNA for degradation. Activities of RBPs are regulated by extracellular signals (eg. growth factors, hormones). RBPs control other key RNA processes – splicing, maturation, transport, and translation.

37
Q

How is mRNA degradation initiated?

A

mRNA degradation is usually initiated by de-adenylation of the poly-A tail followed by 3’ to 5’ exonuclease digestion which is then followed by 5’ to 3’ exonuclease digestion which follows the removal of 5’ meG ‘cap’.

38
Q

Describe the difference in mRNA between eukaryotes and prokaryotes

A

In prokaryotes, most mRNAs have short half-life (minutes). In eukaryotes, different mRNAs are degraded at different rates and can be a point of control of gene expression.

39
Q

What are AREs?

A

AREs: AU-rich sequences near 3’ ends

40
Q

What are RBPs?

A

RBPs: RNA- binding proteins

Year 2: Genetics (14 decks)

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