DNA Transcription

What is a gene? Compare and contrast between eukaryote and prokaryote genes

Gene - region of DNA that encodes for protein or RNA product

Prokaryotes

• 2000 base pairs

• 3000 genes

• avg density 80%

Eukaryotes

• 150000 base pairs

• 25000 genes

• avg density 10% (more empty space)

Prokaryote gene

operon - set of genes under one promotor and operator

Eukaryote gene

has introns and extrons, introns are spliced out

Template and coding strand

template strand - 3’ to 5’

coding strand - 5’ to 3’ (same as mRNA, T —> U in RNA)

Transcription in Prokaryotes

Innitiation

• Sigma factor - helps RNA polymerase find promotor

• holoenzyme - starts transcription at promotor

promotor sequences

• -10 TATAAT

• -35 TTGACA

Elongation - RNA polymerase unzips dna

• rudder unzips helix

• zipper allows for mRNA to exit channel

Termination

• Hairpin loop snaps transcript off

• CG (3 H bonds) followed by uracils

• AU (2 H bonds) weaker

Trascription in Eukaryotes

Innitation

GTF - Helps RNA Pol II find promotor

GSTF - Specific transcription levels (activator/repressor)

promotor sequences

• core region (+40 to -50)

• proximal (-50 to -200)

• distal (-200 to upstream)

Termination - RNA polymerase II has long tail that’s phosphorylated

• CPSF finds cleavage site

• CSTF cuts tail

mRNA processing

only in eukaryotes

• 5’ end modified by cap - recognition signal for translation

• introns are spliced out

• poly A tail added to 3’ end

Splicing process

spliceosome - proteins and SRNPS

1. sRNPs bind to start and end of introns

2. introns form loop (lariat)

3. lariat is cut off, exons join together

Why significant for human genes? What’s the benefit?

• Allows for alternative splicing, choosing which exons to join together to make more proteins