BMP: Transcription

Question 1

What is transcription

Answer 1

• Trascription is the synthesis of RNA from a DNA template, catalysed by RNA polymerase

Question 2

What is the relationship bettwen DNA and RNA synthesis?

Answer 2

• Processes are identical apart from trascription can occur in the absence of a 3’OH group

Question 3

What forms of human RNA polymerase is there?

Answer 3

• RNA pol I: makes large rRNA (18S/28S)
• RNA pol II: Makes all mRNA
• RNA pol III: Makes small rRNA (5S/5.8S) and tRNA

Question 4

What do each of the DNA strands act as?

Answer 4

• A coding or template
• The template is used to transcribe the RNA
• The transcribed RNA has an identical base sequence (except U insread of T) and orientation (5’ to 3’) to the coding strand

Question 5

In order for transcription to take place what must RNA recoginize?

What is used?

Answer 5

• Where the start site for transcription is
• Which is the template strand
• What genes to transcribe as most genes are normally switched off
• The start site signals that exist in DNA are called promoters and they are short sequences of specific bases

Question 6

In general what is the purpose of a promoter?

Answer 6

• Emcompesses the RNA start site and directs the accurate initation of transcription

Question 7

What is the purpose of gene regulation?

Answer 7

The ability to swtch genes on and off allows for the cell/organism to respond to physiological changes

Question 8

What does the promoter contain?

Answer 8

• Contains a considerable consenus
• A consenus sequence is the sequence most commonly found in a given region of many genes
• TATA (A/T)

Question 9

What does the promoter contain?

Answer 9

1. TATA box:
   
   • DNA sequence found in the promoter region of genes. TATA(A?T)A sequence is recoginzed by TF_IID (TBP) and is loated at -23 ie 25 nucleotides upstream from the first coding nucleotide
2. TF_IID:
   
   • GC rich sequence occuring at -35
3. Initation element:
   
   • ​​ALso reconised by TFIID and site at which RNA pol II initates transcrioption
4. Downstream elements:
   
   • ​​E.g. Motif 10 (MTE) or downstream promoter elements (DPE)
   • Basal transcription factors bind to these promoter regions facilitating RNA pol II attachement

Question 10

What happens if there is a mutation in TATA box or DPE?

Answer 10

• MTE functions idenpently to DPE and TATA box. Therefore if there is a loss of transcriptional activity due to mutation in TATA or DPE, additino of MTE can compensate this
• However, the MTE exhibits strong synergism with the TATA-box as well as the DPE. Additional gene-specific transcription factors (e.g. hormones, cytokines etc.) provide specificity to transcription.

Question 11

What is the primary transcript called?

What happens to it?

Answer 11

The heterogenous nuclear RNA - under goes extensive post-transcriptional modifcation

Question 12

Describe capping and the purpose

Answer 12

• Capping of the 5’ end occurs as soon as transcribed
• A methylguanosine joins to the first transcribed tucleotide via a 5’-5’ triphosphate bridge
• It serves to decrease degradation rate of mRNA and also assit with correct positioning to the ribsome during translation

Question 13

What different capping exist?

Question 14

What other post-transcriptional modifcatinos occur

Answer 14

• At the end of the hnRNA a sequence is produced call polyadenylation signal
• Immediately upon terminatio of transcription an enzyme complex recoginises and binds to this signal. The hnRNA is clevaed arounf 10-20 nucleotides downstream from this signal and follwed by addition of adenosine nucleotides
• Around 250 nucleotides are sequentially dded catalysed by poly(A) polymerase. The poly(A) tail protects the mRNA from degredation

Question 15

Describe splicing

Answer 15

Splicesomes remove introns (non-coding refions) and goin exons (coding regions) togethrr