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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 of molecular biology: information flows from gene to protein. |
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. |
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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 |
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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 |
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