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Transcription translation steps11/11/2023 This is produced in the lagging strand by an RNA polymerase (called DNA primase) that is able to use the DNA template and synthesize a short piece of RNA around 20 bases in length. Strangely, DNA polymerases cannot initiate DNA synthesis de novo, but require a short primer with a free 3'-hydroxyl group. Bacteria have at least three distinct DNA polymerases: Pol I, Pol II and Pol III it is Pol III that is largely involved in chain elongation. The resulting short strands are called Okazaki fragments (after their discoverers, Reiji and Tsuneko Okazaki). The leading strand is synthesized continuously but the opposite strand is copied in short bursts of about 1000 bases, as the lagging strand template becomes available. A portion of the double helix must first unwind, and this is mediated by helicase enzymes. This makes it impossible for DNA polymerases to synthesize both strands simultaneously. The Central Dogma of Molecular Biology states that DNA makes RNA makes proteins ( Figure 1).ĭNA replication in bacteria Simplified representation of DNA replication in bacteriaĭNA biosynthesis proceeds in the 5'- to 3'-direction. This is a fascinating subject that is certain to advance rapidly over the next few years. Some of this non-coding DNA controls gene expression but the purpose of much of it is not yet understood. The nucleotide sequence of the human genome is now known to a reasonable degree of accuracy but we do not yet understand why so much of it is non-coding. These regions are called introns and make up around 95% of the genome. Large stretches of DNA in the human genome are transcribed but do not code for proteins. The human genome contains around 30 000 genes, each of which codes for one protein. This is known collectively as the human genome. In humans, the nucleus of each cell contains 3 × 10 9 base pairs of DNA distributed over 23 pairs of chromosomes, and each cell has two copies of the genetic material. The genetic material is stored in the form of DNA in most organisms.
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