Molecular biology and genetics final review - Molecular biology and genetics final review DNA structurelectures 1 and 2 Averywork proves that DNA is the

Molecular biology and genetics final review - Molecular...

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Molecular biology and genetics final reviewDNA structure—lectures 1 and 2Avery—work proves that DNA is the genetic materialProvided proof that DNA mediates transformationFractionated extracts from heat killed IIIS cells and tested for transformation activity by mixing with IIR cellsCould remove proteins, lipids, polysaccharides and ribonucleic acid without affecting transformation activityDestruction of DNA with DNase destroyed the transforming activityPrepared DNA from dead IIIS cellsTreated the DNA with different enzymesMixed treated DNA to cultures of IIR cellsTherefore DNA was the “transforming Principle”Hershey-Chase experiment—work shows that DNA is the genetic material of phage T2Bacteriophage T21.50% protein and 50% DNA2.Phage tail binds E. coli3.Progeny viruses produced in the infected cell4.Bacterium lyses to release progeny virusKnew from other work thatPhages attach to bacteria by their tailsOsmotic shock ruptures the phage producing an empty-headed phage ‘ghost’ that is non infectiousAgitation of phage and bacteria in a waring blender prevents infectionIt is the phage protein or phage DNA thatis responsible for the generation of progeny phage particles“These facts show that the bulk of the sulfur remains at the cell surface during infection, and takes no part in the multiplication of intracellular phage. The bulk of the phage DNA, on the other hand, enters the cell soon after adsorption of phage to bacteria”Therefore genetic material in phage T2 is DNA notproteinDNA structural propertiesDNA is composed of nucleotides—nitrogenous base + sugar + phosphatePyrimidines are single ringed nitrogenous bases: Uracil, cytosine and ThyminePurines are double ringed nitrogenous bases: Adenine and GuanineNucleotides are joined together to form a DNA polymerJoined by phosphodiester bondsLinks the C-3 of one sugar to C-5 of another sugarThe molecule has a 5’ to 3’ polarity5’ phosphate—3’ hydroxylSame bond is found in RNANumber of guanine equals the number of cytosine (GC)
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Number of adenine equals the number of thymine (AT)DNA has a sugar-phosphate backboneThe bases are joined by hydrogen bonds (2 H-bonds between T and A) (3 H-bonds between C and G)DNA has a hydrophilic exterior (likes water)Base pairs are hydrophobic (do not like water)Strands are complementary—each strand contains the information to produce the other strandDNA PackingSupercoilingSupercoiled DNA is more compactRequires cutting, rotation and rejoiningCollapse into coilsProkaryotic DNA is supercoiled and folded onto an RNA scaffoldEukaryotic DNA is wrapped around nucleosomesNucleosomes are composed of 4 different histonesH2aH2bH3H4Each are present as dimersHistonesHigh content of basic amino acidsHighly conserved amino acid sequence in all eukaryotesReplaced by protamines in sperm
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