DNA primary structure Backbone made of sugar phosphate groups deoxyribose and PO4 Series of nitrogen containing nitrogenous bases that project from the backbone Nucleotide is a ribose a phosphate and a base Directionality one end has a 3 hydroxyl group on the 3 carbon and the other end has an exposed phosphate on the 5 carbon the two ends of a DNA molecule are different Directionality is also called polarity Carbon numbering below 5 carbon loses OH to bond with the PO4 Nitrogenous base attaches to 1 carbon PO4 of one nucleotide attaches to the 3 OH of another nucleotide to start a strand of DNA the 3 carbon loses the OH so it can bond with the PO4 The bond between a PO4 and a deoxyribose is called a phosphodiester bond link http www contexo info DNA Basics images deoxyribose3 gif DNA replication happens in the S ynthesis phase of the cell cycle When two strands of DNA pair up they go in opposite directions one goes 3 to 5 and the other one goes 5 to 3 called antiparallel NTP nucleoside triphosphate Adenosine triphosphate ATP breakdown of ATP is coupled with non spontaneous reactions so the cell can do work Guanine triphosphate GTP substrate in RNA synthesis catalyzes protein synthesis and gluconeogenesis making glucose from things like pyruvate lactate glycerol etc important for G protein signal transduction Cytidine triphosphate CTP substrate in RNA synthesis breakdown is coupled with a few non spontaneous reactions such as making glycerophospholipids cell membrane molecules and the glycosylation of proteins attaching glycans to proteins lipids etc 5 methyluridine triphosphate m5UTP comes from thymidine Uridine triphosphate UTP substrate for RNA synthesis used in the metabolism of galactose dNTP similar to ATP deoxynucleotide triphosphate Like deoxy adenosine triphosphate dATP there s also deoxy guanosine triphosphate dGTP deoxy cytidine triphosphate CTP and deoxy uridine triphosphate UTP Those are all dNTPs DNA replication Helicase splits the DNA strands apart Messelson Stahl ExperimentTo find out how DNA replicates in bacteria and theoretically everything else 1 Start they kept the bacteria in an environment with only N15 nitrogen with an extra neutron so that the DNA only had N15 in it a Hypothesis 1 conservative the DNA splits to replicate but the new strand and the old strand stay separate F1 half N15 and half N14 no mixed F2 N15 and N14 no mixed N b Hypothesis 2 non conservative DNA separates replicates and recombines randomly F1 DNA with N14 and 15 together no particular ratio F2 same as f1 c Hypothesis 3 semi conservative DNA strands separate and 2 For one generation they transferred the bacteria to an environment with only N14 so they could see how the weight of the DNA changed and therefore figure out how the DNA replicates a Results the new generation f1 of bacteria had DNA that was N14 5 the DNA had a mix of N14 and N15 b The f2 generation three quarters of the DNA was N14 only and one quarter of the DNA had mixed N 3 This disproved non conservative theory and conservative theory which only left semiconservative so that one is right 4 Science is always like well it can t be anything else so I guess it s the last option Bacterial DNA is circular because it is often floating around in the cytoplasm and the circular shape prevents degradation and damage There is a sequence that is the origin of replication where everything starts and then DNA replicates DNA replication process Leading strand starts on the 3 strand goes 5 to 3 continuously without any problems Lagging strand is 5 to start so the DNA