ously. Termination of DNA replication occurs with the replication enzyme telomerase, which adds telomere repeats at the end of the lagging chain.
3. Transcription is the process by which RNA chains are made from DNA templates (Devlin, 1997, 689). The reaction is catalyzed by enzymes known as RNA polymerases which do not require a primer molecule. The reaction takes place in the cell nucleus or the mitochondrial matrix in eukaryotic cells. Transcription takes place in three parts: the initiation phase is when the RNA polymerase recognizes an active gene starting point and the bond formation process begins; the elongation phase is the actual synthesis of the RNA chain; the third phase is the termination and release phase, where the transcribed chain is ended and released from the DNA chain it has transcribed.
Each transcription begins and ends with the recognition of specific sites on the DNA template (Devlin 1997, 690). Start regions are known as promoters. RNA polymerases all synthesize RNA in the 5' to 3' direction. In eukaryotes, several molecular events other than the RNA polymerase binding are required to initiate transcription. Chromatin containing the promoter sequence must be spatially accessible to the transcription machinery. The transcription factors must bind to sequences in the promoter region for a gene to be active. Enhancer sequences some distances away from the promoter sequence also must bind protein factors to stimulate transcription.
Once transcription of the DNA template to mRNA has taken place, translation is the step that converts the code on the mRNA sequence into amino acids for protein biosynthesis (Devlin, 1997, 714-733). The translational process is read from the 5' end to the 3' end, and the amino acid sequences are biosynthesized from the amino-terminal residue to the carboxy terminus. Translation takes place in the cytoplasm on the ribosomes. Initiation of synthesis begins with the bri...