Lecture 22 -- Transcription and Translation

1) prokaryotic mRNA is continuous, while eukaryotic mRNA is segmented with introns and exons. the mRNA undergoes splicing, where the introns are removed and the exons are ligated together

2) in eukaryotes, transcription occurs in the nucleus and then migrates out to the endoplasmic reticulum in the cytoplasm for translation. while in prokaryotes, transcription and translation occurs at the same time at the same place, since prokaryotes have no membrane bound organelles

3) eukaryotes have post-transcriptional modification in which a cap is added to the 5' end and a poly-A tail is added to the 3' end (all occuring in the nucleus)

Regulatory sequences that are on the same molecule of DNA as the gene being transcribed

Promoters -- bound RNA polymerase II
enhancers -- bound by transcription activators
silencers -- bound by transcription repressors

Open -- it binds nonspecifically to the template

closed -- it is readed to begin transcribing

Anti-sense --> template DNA strand

sense --> coding strand (so the other strand of DNA that is not being used as a template)

In trancription, uracil (U) replaces thymine (T) and binds to adenine (A)

At the +1 site in the DNA sequence

-10 box --> TATAAT

-35 box --> TTGACA

Rho-dependent termination

rho-independent termination

1) RNA polymerase binds to DNA
2) sigma factor binds to RNA polymerase (together called RNA polymerase holoenzyme). The sigma recognizes promoter sites and binds to it
3) DNA unwinds at the -10 site to form an open complex
4) short RNA is made
5) sigma dissociates
6) polymerization proceeds

It is the same as the sense strand (which is the coding strand

Sigma factor helps RNA polymerase find the promoter sites

RNA polymerase slides down the DNA template strand from 3' to 5', therefore mRNA is synthesized in the 5' to 3' direction

They are continually expressed

From one transcript, 3 proteins are made:

1) beta-galactosidase
2) permease
3) transacetylase