BIS 101 Lecture 2: RNA Processing

RNA processing is done by …

eukaryotes

…. RNA polymerase is more complex than …. RNA polymerase

eukaryotic RNA polymerase is more complex than Prokaryotic RNA polymerase

what are the 3 types of eukaryotic RNA polymerase?

• RNA pol 1: transcribes ribosomal RNA (rRNA) = non coding RNA

• RNA pol II: transcribes mRNA = coding RNA

• RNA pol III: transcribes transfer RNA (tRNA) = non coding RNA

describe how eukaryotes initiate transcription?

1. the transcription factor binds to the TATA region of the promoter.

2. then a protein binds to the transcription factor, then another and many more until the full comlplex RNA polymerase had binded to the transcription factor.

3. then the RNA polymerase is ready to begin transcribing.

what is a transcription factor?

what do they do?

protein that binds to DNA

• they regulate regulate transcription initiation

• help recruit RNA polymerase to promoter region

what is a general transcription factor?

is their impact local or global?

all the transcription factors that are REQUIRED for transcription initiation by RNA polymerase

there is a different set of GTFs required for initiation for each RNA polymerase (I,II,III)

global impact

what is a specific transcription factor

is their impact local or global?

regulates transcription initiation for a subset of genes or in a given cell type or developmental time

local impact

how are transcription factors that interact with RNA polymerase 2 named

TF2

trans acting vs cis acting mutation

trans acting mutation affect the gene itself and other genes

Cis acting only affects itself.

eukaryote vs prokaryote transcription

Eukaryote:

• 3 RNA polymerases

• complex initiation regulation

• occurs in nucleus

• transcription and translation is compartmentalised

Prokaryote:

• only 1 RNA polymerase

• Relatively simple initiation

• occurs in cytoplasm (prokaryotes have no nucleus)

• transcription is coupled with translation

what are the 3 steps of mRNA processing

does it occur in prokaryotes or eukaryotes?

• splicing

• 5’ cap

• addition of polyA tail

• It occurs in eukaryotes.

what is the 5’ cap

why is it added to pre mRNA

• 5’ cap is a modified guanine nucleotide that is added to the 5' end of pre-mRNA

• to protect mRNA from degradation

• required for nuclear transport

• facilitates intron splicing

• enhances translation effiency

what is the polyA tail

why is it added to pre mRNA

• The polyA tail is a string of adenine nucleotides added to the 3' end of pre-mRNA.

• it is not transcribed (did not come from DNA sequence)

• added my enzymes

• It protects 3 end of mRNA from degradation

• required for nuclear transport

what is splicing?

removing introns by splisosomes from pre mRNA

and joining of exons

what are introns and exons?

Exons: nucleotide sequences that code for amino acids

(open reading frame: “ORF” → codons of nucleotides)

Introns: nucleotide sequences that are transcribed but do not code for amino acids (largely absent in bacteria)

describe the process of splicing

1. spliceosome binds onto an intron on the pre mRNA → it removes the intron into a lariat structure (removed intron)

2. all introns are removed → mature mRNA

how are the ends of the exons bonded

via nucleophillic attack

2’ OH group on the ribose sugar does nucleophilic attack on the 3’ OH group on the 5’ splice site