Sunday, April 24, 2011

Genetics: Protein Synthesis: Transcription (2)

RNA Polymerase is the enzyme responsible for transcription.
There are 3 types of RNA Polymerase:
1)RNA Polymerase 1: makes ribosomes (transcribes rRNA) (non-structural)
2)RNA Polymerase 2: transcribes mRNA (structural)
3)RNA Polymerase 3: transcribes tRNA(non-structural)

The steps:

1) Initiation:
Transcription factors first bind to the promoter region of the gene. Transcription factors are groups of proteins that bind to a gene turning off/on transcription according to the bodies needs. The promoter region is a sequence of nucleotides that come before the gene. It includes the TATA box. The RNA Polymerase then also bonds to the location and the initiation complex is formed.

2) Elongation:
RNA Polymerase adds complimentary base pairs to one strand (the template strand) making a copy of the coding strand (with the exception of thymine which is replaced by uracil). Synthesized 5 prime to 3 prime.

3) Termination:
New RNA strand is completely released from template strand. DNA finishes recoiling.

4) Post Transcriptional Processing:
Splisosomes cut out unnecessary info (introns) and remaining useful info (extrons) are rejoined. Now the pre-RNA becomes mRNA through the addition of some features for protection. A modified guanine cap on the 5 prime side and a poly-A tail on the 3 prime end.

The mRNA now passes through the nuclear membrane and into the cytoplasm where it prepares for translation!

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