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Medicine 1.2 > Gene Expression > Flashcards

Gene Expression Flashcards

1
Q

What is the central dogma of molecular biology?

A

Dna is transcibed to RNA, the RNA is translated into proteins.

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2
Q

What are some exceptions the the central dogma of molecular biology?

A
  • Retroviruses which use reverse transcriptase do the opposite
  • Some RNA also function as RNA and does not need to be made to protein eg. tRNA, rRNA, miR
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3
Q

What is a genome?

A

A sequence of all the DNA in an organism

Genes + non-coding regions

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4
Q

What is the structure of a gene?

A

A gene is a sequence of letters and contains exons and introns, we keep exons and get rid of introns when protein coding.
Genes will have RNA coding region and a slightly smaller protein coding region.
In the untranslated region you have things like cap addition site and polyA addition site.

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5
Q

What are the 3 steps of transcritpion?

A
  • Initiation
  • Elongation
  • Termination
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6
Q

What happens during initiation stage of transcription?

A

RNA polymerase II to the start of the gene, DNA strands pulled apart.

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7
Q

What happens during elongation stage of transcription?

A

RNA gets longer - it forms a transcription bubble.

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8
Q

What happens during termination stage of transcription?

A

RNA synthesis stops

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9
Q

What happens after termination stage of transcription?

A

Primary RNA transcript (pre mRNA) includes introns.
Processing in nucleus leads to addition of 5’ cap and 3’ polyA tail.
Splicing by spliceosome removes introns.

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10
Q

Where will mRNA export to after translation?

A

Cytoplasm

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11
Q

What are transcription factors?

A

Are proteins that bind to short but very specific sequences of DNA.

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12
Q

What are transcription factors function?

A

They affect rate of transcription, turn genes on or off, can act as activators and repressors.
They are like the master regulators and so mutations in TF’s or TF binding sites underline many diseases.

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13
Q

What are examples of transcription factors?

A
  • p53 and E2F in cell cycle
  • Nuclear hormone receptors - ligand dependant transcription factors: - glucocoticoid receptor
  • oestrogen receptor
  • testosterone receptor
  • retinoic acid receptor
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14
Q

What can possibly act as treatment on inactive transcription factors?

A

Steroids

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15
Q

What is needed in initiation phase for it to begin?

A

We need transcription initiation complex (TIC) as RNA polymerase II can’t bind directly to DNA.
General or basal transcription factors act as a bridge (eg. TFIIB, TBP bound to TATA box)

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16
Q

Where do transcription factors bind?

A

The sequence ahead of a gene called the promoter, the CAT and TATA box are here.

17
Q

What are some examples of mutations in the promoter sequence of a gene and its outcomes?

A

Human beta globin gene

eg. Mutation in TATA box of HBB can cause thalassaemia (severe anemia)
eg. Mutation in CCR5 promoter; affects rate that HIV progresses to AIDS
eg. Mutation in factor IX promoter can cause haemophillia B
eg. Mutation in LDLR promoter can cause familial hypercholestorlemia

In all eg’s, mRNA sequence and protein structures in NOT changed, but ammount of mRNA made is required.

18
Q

What are enhancers and silencers?

A

DNA sequences where transcription factors bind to affect rate of transcription.
Can be upstream or downstream of a gene and can be close or far away.

19
Q

What are the function of enhancers and silencers?

A

They make it more or less likely that a promoter will be activated.
Are required for expression of most genes.

20
Q

What are some examples of enhancers(activators) and silencers(repressors) ?

A
  • p53; -activator of transcription of p21 > cell cycle arrest and DNA repair
  • repressor of transcription of survivin > apoptosis
  • E2F; - activator of transcription of genes needed for S phase eg. lamins
  • Oct-1; repressor of transcription of TSH in all cells apart from thyrotrophs
  • Snail; repressor of e-cadherins in epithelial cancers > less cell-cell adhesion, more invasive ability
21
Q

What is a clinical example mutation in a genes enhancers ans silencers?

A

EG. myc

Mutations called single nucleotide polymorphisms (SNP) frequently found in enhancers or silencers.

22
Q

What are the higher level of regulation of gene expression?

A

There is closed and open DNA; DNA is not always accessible to TF’s.
So DNA is not always accesible to TF’s as nucleosomes keep DNA closed.

23
Q

What do locus control regions (super enhancers) do?

A

Open chromatin spanning several genes,

24
Q

What is an example of LCR in use in a gene?

A

Eg. globin genes;
transcription factors bind to globin LCR (only in RBC’s)
-opens DNA of all globin genes
-Gene expression now possible

25
Q

What is the clinical significance of mutation in LCR of globin gene?

A
  • Mutations in LCR
  • Locus stays closed, globin expression very low
  • Can lead to hispanic thalassaemia
  • No mutation in globin gene, but amount made is affected
26
Q

What is a constitutive gene?

A

Genes which are expressed in all cells, all the time at about the same level.
These are housekeeping genes that maintain basic cell function.
They have a constitutive promoter

27
Q

What are inducible genes?

A

Genes which are only expressed in certain tissues or cells, only expressed at certain times.
They use spatiotemporal gene expression.

28
Q

What are some examples of constitutive genes?

A
  • Beta actin (microfilaments)
  • General/basal transcription factors
  • Ribosomal proteins
  • Glyceraldehyde - 3 - phosphate dehydrogenase (GAPDH) in glycolysis
29
Q

What are some examples of inducible genes?

A
  • lots of protein coding genes
  • cell specific; CD4, CD8, collagen 1 and 2
  • time specific; cyclins, melatonin, inflammatory cytokines
30
Q

How does one gene produce multiple proteins?

A
  • Splicing

- Alternative splicing

31
Q

What is splicing?

A

Removal of introns by spliceosome

Is a complex but precise process

32
Q

What is alternative splicing?

A

More than 90% of proteins coding genes produce multiple isoforms (different mRNA’s from same gene).
Same exons in different orders or incomplete version or addition of extra exons, introns may be kept in.

33
Q

What is an example of post transcriptional reglation?

A

MicroRNA’s

  • Short RNA sequences
  • Complementary binding to mRNA to initiate destruction of mRNA.
  • Can reduce gene expression after transcription
  • Involved in pathogenesis of cancer and other diseases
34
Q

How can analysing the genome help in care?

A

Sequence of DNA coding for proteins or sequence of regulatory elements can be used to see ammount of proteins patients will express and analyse whether they express normal or mutant versions.

35
Q

What is the transcriptome?

A

All the mRNA’s in a given cell/tissue at a given time.

36
Q

What is the clinical application of analysing the transcriptome?

A

Can help differentiate between diseases such as prostate and breast cancers.

37
Q

What is the proteome and what can it be used for?

A

All proteins in a cell/tissue/tumour

It can be profiled and used for diagnosis, prognosis and treatment selection?

Medicine 1.2 (22 decks)

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