chp 1-10

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Cell and Systems Biology

DNAwas proved to be genetic material with bacteria that had smooth and rough colonies. Smooth colonies-> lethal; rough->non lethal DNA= nucleic acid= has nitrogenous base, joined to pentose sugar ring, rings attached by phosphates Purine=G&A--> double ring; pyrimidines C& T Single ring;;; purines must bind with pyrimidines How did they find out DNAwas double stranded? Watson and Crick had 3 observations: DNAis a polypeptide made of phosphate groups; sugar and bases X-ray diffraction data of DNAcrystals showed that DNAwas long and skinny; had two parts that were parallel Because of double stranded DNA Purine G&A; and Pyrimidines C& T -Abasepairs with T (2 H bonds) Therefore only one origin of replication; Eukaryotes have many origins of replication because linear chromosomes time (because have to replicate the DNAin less than 8 hours DNAis read: 3->5 DNAis synthesized 5->3ALWAYS Lagging strand is made discontinuously and produces Okazaki fragments; leading strand is made continuously Steps of DNAreplication; 1. the DNAstrands are denatured unwound at origin of replications (generallyA-T rich; by enzymes that unwind the DNAcalled helicases 2.binding proteins keep the DNAin a single stranded form-- do not cover bases so replication can occur 3.addition of an RNAprimer by Primase(makes RNAprimer) DNApolymerase can only add to a pre-existent strand, cannot start synthesis 4.Polymerization template read 3->5 and new strand is made >3; Okazaki fragments produced 5.Joining of DNAby Ligase DNApolymerase has proofreading ability; but polymerization and proofreading occur at two sites; proofreading ensures correct nucleotide is being added and if anything goes back and takes it out before adding another Repair mechanisms have evolved to ensure good replicated DNA-- DNAglycosylase recognizes unnatural bases and repairs them Mismatch repair r removes replication errors and sues the old strand as a template the repair the new one -recognizes and excises the damaged strand to leave a gap; 2.polymerase fills in the gap;3. Phosphate backbone is joined by ligase ---> picks the strand with no nicks!!! (the new strand! As we get older, the more mutations we accumulate and higher the chances there'll be a deleterious mutation e.g. cancer DNAsustains insults daily! DNAalways undergoing damage spontaneously 2 spontaneous damage are: Depurination (loss of G orAbase from DNA) Damination (loss of NH3 converting C into U) Or because of UV radiation can haveAThymine Dimer (covalent bonding of 2 adjacent thymines) ---> may cause a block in transcription replication
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