TRANSLATION AND TRANSCRIPTION


Website:
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Translation.html
http://www.rothamsted.ac.uk/notebook/courses/guide/trans.htm
http://biowiki.wikispaces.com/Translation
http://biowiki.wikispaces.com/Transcription
http://bernardibo10.wikispaces.com/Transcription+and+translation

Transcription is a complex process which utilizes RNA polymerase. The RNA polymerase bind to the correct promoter, and this initiates transcription. Then, the process of elongation occurs. This is when additional nucleotides are added to the 3' end of the growing RNA molecule. This elongation process continues until termination, when the RNA polymerase is separated from the template DNA strand, and the synthesized RNA strand, because it recognizes a termination sequence. There are several methods which allow the modify the RNA such as: Capping, Addition of poly A-trail, methylation, cleavage of big RNAs, and splicing. Capping is basically the addition of 7-methylguanosine, which protects the RNA from degradation. The addition of the poly-A tail also serves to decrease degradation of the RNA. Methylation is the addition of methyl groups. Cleavage of the big RNA's is when transcription is terminated correctly, and thus the transcript must be cut, while it is in the process of being transcribed. Splicing basically removes introns, which serve no purpose in genes. The exons are the expressed sequences which are necessary.

There are three steps to translation. The first step is initiation. This is when the small subunit of the ribosome binds to a site “upstream” of the start of the message. Then it proceeds downstream until it reaches the start codon which is AUG. Afterwards, it is joined by the large subunit and the tRNA which carries the respected amino acid of the codon. The tRNA binds to the P site on the ribosome. The next step of translation is elongation. This is when the next tRNA arrives at the A site. Afterwards, the preceding amino acid is covalently linked to the incoming amino acid with a peptide bond using ribozyme. Then, the tRNA is released from the P site and the ribosome continues to move down downstream one codon at a time. The last step of translation is termination. This is when the ribosome reaches one or more STOP codons. The protein release factors recognize this codon when they arrive the A side and thus release the polypeptide from the tRNA. The ribosome is split into its subunit and which can later be reassembled for another round protein synthesis.

external image c7.17.7b.transcription.jpg&usg=AFQjCNH7CaryER84iWguZcV_ItJPA5WdvA
http://fig.cox.miami.edu/~cmallery/150/gene/c7.17.7b.transcription.jpg

external image translation.jpg
http://kvhs.nbed.nb.ca/gallant/biology/translation.jpg