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)
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.
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.
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!