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Transcription Cheat Sheet by

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Transc­ription

RNA: extended from 5' to 3'; single­-st­randed;
Transc­ription initiates at promoters: binding of RNA polyme­rase, accessory proteins
The process of transc­ription consists of initia­tion, elonga­tion, and termin­ation
5'-cap­ping, 3'-pol­yad­eny­lation
Transc­ription is the synthesis of RNA from a DNA template
DNA need to be unwrapped from histone core for transc­ription to proceed

Central dogma

Central dogma

Central dogma of molecular biology: inform­ation flows from gene to protein.

Transc­ription

Transc­ription

RNA polymerase adds ribonu­cle­otides to 3'-OH end, following Watson­-Crick base pairing
The RNA strand is comple­mentary and antipa­rallel to the DNA template.
U instead of T is used.
 

Transc­ription Requires:

RNA polyme­rases: enzymes that catalyze the synthesis of RNA
Accessory proteins: e.g. sigma factor, general transc­ription factors
DNA template
Ribonu­cle­otides

Functions of RNAs

All RNA come from transc­rip­tion.
Only mRNA produce protein.
mRNA
Nucleus and cytoplasm
Carries genetic code for proteins
tRNA
Cytoplasm
Helps incorp­orate amino acids into polype­ptide chain
rRNA
Cytoplasm
Structural and functional components of the ribosome

A transc­ription unit

 

Initiation

1. RNA polymerase binds to promoter DNA sequences
2. RNA polymerase separates the DNA strand to create a transc­ription bubble (promoter opening)
3. Ribonu­cle­oside tripho­sphate are added
4. Polymerase moves past the promoter and becomes stably bound to DNA (promoter clearance)

Elongation

1. RNA polymerase moves along template strand and elongate the RNA transcript
2. RNA polymerase unwinds duplex ahead of it to expose single strand template. DNA strands behind RNA polymerase pairs again to reform DNA duplex.
3. The growing RNA transcript is extruded through the RNA polymerase

Termin­ation

RNA polymerase dissoc­iates from DNA template when it encounters a terminator sequence.

Pre-mRNA

Longer than mRNA
1. Addition of 5' cap
2. Addition of poly(A) tail
3.RNA splicing
introns removed, exons spliced together

mRNA splicing

 

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