Week 8 Notes
Week 8 Notes BSC 114
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This 2 page Class Notes was uploaded by Rebecca Sharp on Friday April 1, 2016. The Class Notes belongs to BSC 114 at University of Alabama - Tuscaloosa taught by Stevan Marcus in Winter 2016. Since its upload, it has received 26 views. For similar materials see Principles Of Biology I in Biological Sciences at University of Alabama - Tuscaloosa.
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Date Created: 04/01/16
DNA Replication DNA replication works because of its double helix structure. They’re equal and opposite, so each strand is capable of building a copy for itself. First the strands are separated, by DNA polymerase. Next, the bases are copied so each A ends up with a new T, and each C ends up with a new G. Finally, the nucleatides bond to create the sugar phosphate backbones that keep DNA looking like itself. The place two strands of DNA are separated is called the replication bubble. That’s where DNA replication begins. Bacteria usually only have one origin of replication, but eukaryotes can have thousands of origins of replication. Replication works in both directions, and continues until the entire molecule is completely copied DNA polymerase only works from the 5 to 3 direction, so the ‘leading’ strand is synthesized in the 5 to 3 direction and the lagging strand is synthesized in the 3 to 5 direction. The leading strand is continuous, the lagging strand is synthesized in segments called Okazaki fragments, usually only 100 to 200 nucleotides long. They’re joined by DNA ligase. At the end of a replication bubble is a replication fork, where new DNA is synthesized. The trademark double helix structure that makes DNA DNA gets unwound here by helicase. Helicase can make the double helix a little frenzied, a little frantic, so an enzyme called topoisomerase works to correct over winding. Primase is what actually starts DNA synthesis, polymerase only adds nucleotides to the 3 end on an established DNA thread. Genetics Based on triplets called codons. Its three nucleotides together that code for a specific amino acid. The process isn’t perfect, so even when our cells mess up a little bit we can still end up with the amino acid. For example, there’s six different triplets that will code for Leucine. Because this coding is so simple, it’s possible to plant genes across species like putting fire fly genes into a plant, or putting bioluminescence into a pig. All About Trancription Transcription has three basic parts; initiation, elongation, and termination In initiation, the polymerase unwinds DNA 10-20 bases at a time so that RNA can get to it. This begins at a place called the TATAAA box, where transcription is initiated In elongation, the RNA is synethesized. Remember, synthesis only happens in the 5:3 direction. Transcription moves at the breakneck pace of 40 nucleotides per second Termination is the part where the completed RNA strand is released and the polymerase detaches, signaled by a terminator Genes can be transcribed by multiple RNAs at a time because of the way DNA polymerase unwinds the double helix Transcription adds heads and tails to the RNA segments it generates to protect it during transport. A guanine nucleotide at the 5 prime end, called the 5 prime cap, and a poly adenosine tail at the 3 prime end, called the poly a tail The sequences also have long useless sections called introns, or sometimes interveneing sequences. These are cut off by molecules called ‘spliceosomes’, along with the cap and tail, leaving only the coding genes which are called the exons. The exons express a gene. The resulting protein is a continuous protein coding sequence. There is an accepted sequence of introns and exons, Exon1, Intron, Exon2, Intron, Exon3. The leftover material is recycled into the cell fro repurposing
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