Transcription and its human diseases Flashcards Preview

Module 102: Molecular cell biology > Transcription and its human diseases > Flashcards

Flashcards in Transcription and its human diseases Deck (19)
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1

Three types of RNA polymerase

RNA Polymerase i
RNA Polymerase ii
RNA Polymerase iii

2

RNA Polymerase i

Transcribes genes coding for RNA

3

RNA Polymerase ii

Mainly used polymerase

Involving in transcribing protein-coding genes, miRNA and small RNAs

4

RNA Polymerase iii

Involved in transcribing tRNA genes: related to cancer progression as there is an increase in tRNA production to make more cancer proteins

5s RNA genes and small RNAs

5

What molecules inhibit RNA Polymerase ii

Amanitin and other amatoxins, usually found in toxins.

The prevents transcription of proteins and leads to death by liver failure.

6

Cancer

Uncontrollable cell proliferation due to mutations in the genes regulating cell development.

7

Transcription factors

Molecules required to bind to DNA before transcription can begin.

8

Basal transcription factor step of transcription

Basal transcription factor binds to DNA at TATA. This is the promoter region before the gene.

This enables RNA polymerase to bind after.

9

C-terminal domain

Carboxyl terminal domain, tail like structure, on RNA polymerase ii.

When phosphorylated after RNA polymerase binds in transcription, the tail moves down.

Enables RNA polymerase ii to initiate making mRNA.

The domain allows the co-ordination of:
Capping
Splicing
Polyadenylation

10

Capping

Adding a modified nucleotide at the 5' end of primary mRNA.

This keeps it stable for later translation

11

Polyadenylation

A specific sequence of mRNA is recognised

RNA section is then cleaved off by a protein complex.

Poly(A) is then made by a protein complex and is added to the 3' end of the primary mRNA.

Poly(A) is a string of adenine bases

12

Formation of mature mRNA

Splicing:

Pre-mRNA contains introns which are cut out by spliceosomes. Occurs at AG|G

Exons junction complex binds at sites where exons have been joined.

Alternate splicing can occur which exchanges the order of exons.

13

Transport of mRNA out of nucleus

Mature mRNA leaves the nucleus via the nuclear pore and moves into the cytosol.

The cap-binding protein is exchanged for an initiator factor, in preparation for translation.

14

Summary of transcription (7)

1. Basal transcription factor binds at the TATA box before RNA polymerase ii binds.

2. After RNA polymerase ii binds to the promoter region, the C-terminal domain is phosphorylated. Activator protein binds to the mediator.

3. Transcription is initiated.

4. As mRNA is being read, C-terminal domain coordinates splicing, capping and polyadenylation.

5. Introns are removed from primary mRNA whilst a cap is added to the 5' end and a Poly(A) tail is added at the 3' end of mRNA.

6. Exon junction complex holds together the exon sequences. Mature mRNA is formed. This leaves the nucleus into the cytosol via the nuclear pore.

7. The cap on the mRNA is exchange for an initiator protein, ready for translation.

15

Cystic fibrosis caused by transcriptional errors.

Caused by splicing error.

Exon 9 if left out when mature mRNA is formed.

This causes a mild form of CF, which is a loss of function.

16

IGHD II

Isolated growth hormone deficiency II

Genetic disease that occurs from splicing error:

Exon 3 is skipped in the IGHD II pre mRNA due to the substitution of G to U in intron 3

Mutation is dominantly inherited and causes a short stature.

17

Fragile X syndrome

Genetic condition caused by the expansion of CGG in the FMR1 gene, in the X chromosome.

This causes methylation of DNA at the promoter region and prevents RNA polymerase ii from initiating transcription --> gene is silenced.

Symptoms:
Large, protruding ears.
Macro-orchidism
Autism
Learning difficulties

18

Alpha thalassemia

X-linked disease that occurs due to chromatin malformations.

Mutation in ATRX gene, prevents DNA from unwinding properly.

Prevents transcription of alpha globin gene:
Causes mental retardation

19

Beta-thalassemia

Introns are not spliced out properly which causes the premature formation of a stop codon.

This shortens a protein in the haemoglobin and causes anaemia.