DNA -> mRNA = Transcription

The RNA molecule

RNA nt. structure

• A, G, C and Uracil (U)

• Ribose, deoxyribose

Phosphodiester

holds RNA nts. in 5’-3’ direction

• normally single stranded

• can fold (bp) internally

Nucleus

transcription location for Euk. cells

• after synthesis, travels to cytosol

mRNA

messenger RNA = intermediate for protein synthesis

functional RNA

final RNA product has function and is not translated (tRNA, rRNA, snRNA, miRNA…)

Initiation of transcription

overview of gene coding region (2-3%) genome

Gene

genetic information/recipe to make protein

• Humans have 20,000 to 30,000 diff genes

• Each gene has a specific location in genome

• -2-3% of genome codes for protein

• Remaining DNA codes for functional RNA (low %) + involved in regulating gene expression

Locus

a specific location in genome

Gene structure

100s-1000s of base pairs

• only one strand of DNA serves as template for transcription

Coding Strand

non-template

upstream transcription

negative numbers

downstream transcription

positive numbers

transcription start site

starts at +1 start site, 1st nt. to be transcribed

Promoter

Required for Ts but it is NOT transcribed

• Directly upstream +1, on 5’ side of gene on coding strand

• Promoter = binding side (DNA seq.) where RNA pol. binds

Prok. Promoter

DNA Sequence consensus sites =

• -35 site 5’ TTGACAT 3’

• -10 side (pribnow box) 5’ TATAAT 3’

RNA pol. Holoenzyme

binds to promote

• sigma subunit recon. + binds to RNA pol. holoenzyme

• beta subunit recog.

Eukaryotic Promoter

• DNA sequence = TATA box (-25)

• Basal Transcription factors (TF) = proteins that bind to the promoter (TATA) and recruit the polymerase

Synthesis/Elongation of RNA Transcript

RNA pol. opens the strands/unzips the DNA helix

• begins (w/out primer) adding RNA nts. complimentary to the DNA. template (starting @ +1)

Strand is elongated by RNA pol. adding nts. to 3’ end of growing strand

As RNA transcript grows, it dissociates from DNA and DNA helix forms

Coding strand

always the same as mRNA (T’s rather than U’s)

• identical to mRNA transcript

Prok. Termination of Transcription

Transcription ends w/ formation of stem-loop/hairpin loop in transcript

• followed by a stretch of A nts. → causes mRNA to dissociate

Euk. Termination of Transcription

near end of RNA transcript. seq. AAUAAA= term. seq.

• RNA Transcript cut +25 nts. downstream

Prok. product of transcription

mRNA → translation

Euk. product of transcription

pre-mRNA (primary transcript) must be modified before translatiopre-mRNAn

Nucleus

Location of pre-mRNA processing

pre-mRNA processing

• 5’ cap modified guanine (G) added to 5’ end

• Poly-A Tail - 50-250 A. nts. are added to 3’ end

• RNA Splicing

Reason for pre-mRNA processing

modifications are required to protect ends from being chopped up and to export mRNA from nucleus to cytosol

RNA Splicing (intron removal)

• Exons = sequence to be translated

• Introns = sequence removal (spliced out) before

SNRPS

form a complex called a splicosome complex → cut @ junctions. Introns removed, exons spliced together