Presentation on theme: "DNA Information and Heredity, Cellular Basis of Life"— Presentation transcript:
1DNA Information and Heredity, Cellular Basis of Life Chapter 12(M)
2Genes are made of DNA The following scientists proved that DNA is the genetic materialFredrick Griffith (1928)Oswald Avery ( 1944)Hershey and Chase (1952)
3Fredrick Griffith (1928)The discovery of the genetic role of DNA began with research by Frederick Griffith.He studied Streptococcus pneumoniae, a bacterium that causes pneumonia in mammals.One strain, the R strain, was harmless.The other strain, the S strain, was pathogenic.
8When Griffith mixed heat-killed S strain with live R strain bacteria and injected this into a mouse it died.He recovered the pathogenic strain from the dead mouse’s blood.Some harmless bacteria had been “transformed” into the deadly strainFor the next 14 years scientists tried to identify the transforming substance.
9Transforming Substance? Could be:DNAProteinsBecause scientists already knew chromosomes consist of these substances. So the debate started.
10Oswald Avery ( 1944) Treated Griffiths mixture with Protein digesting enzymes remove all proteinsDNA digesting enzymes remove all DNA
11Avery contd. Is Protein the transforming factor? treated Griffith’s mixture of heat treated deadly strain and live harmless strains with protein-destroying enzymes grew the strainsThe bacterial colonies were still transformedConcluded that protein could not be the transforming factor
12Avery contd. Is DNA the transforming factor? treated the mixture with DNA-destroying enzymes grew the strainsThe bacterial colonies failed to transformConcluded that DNA is the genetic material of the cellScientists were still skeptical proteins made of 20 AAs, DNA only 4 bases
13Hershey and Chase (1952)Used viruses to prove that DNA is the genetic material.Viruses consist of a DNA (sometimes RNA) enclosed by a protective coat of protein.To replicate, a virus infects a host cell and takes over the cell’s metabolic machinery.Viruses that specifically attack bacteria are called bacteriophages or just phages.
16Conclusion Phage DNA entered the bacterial cell, proteins did not DNA carries the genetic information.
17The Role of DNAStoring Information The genetic material stores information needed by every living cellCopying Information before a cell divides this info must be copiedTransmitting Information Each daughter cell must receive a complete copy of all the information
19Building Blocks Of DNA Nucleotides A ring-shaped sugar called deoxyriboseA phosphate group (a phosphorus atom surrounded by four oxygen atoms)A nitrogenous base ("nitrogen-containing") : a single or double ring of carbon and nitrogen atoms with functional groups
20Nitrogenous BasesThe four nucleotides in DNA differ only in their nitrogenous basesBases:Thymine (T) single ringCytosine (C) single ringAdenine (A) double ringGuanine (G) double ring
22Structure of DNA Early 1950s R. Franklin Watson & Crick (1953) DNA helix with2 strands with the phosphate linked to the sugar, diameter is 2nm, each turn has 10 basesWatson & Crick (1953)Using Franklins work built a model of DNAEach strand is complementary to the otherA pairs with T, G with C
23Base Pairing Chargaff’s Rule Adenine forms a base pair with Thymine Guanine forms a base pair with CytosineAmounts are about the same
27DNA Strands Two strands double helix Compared to a ladder Sides Sugar phosphate backboneRungs pairs of nitrogenous basesOrder of bases genetic codeDifference in order gives individuality to each living organismBase pairing is the key that allows DNA to be copiedA pairs with T, G with C
29ReplicationComplete set of genetic instructions passes from one generation to the nextThe DNA molecule must be copiedBase pairing allows DNA to be copiedDNA 2 strands, one is used as a templateReplication Process by which DNA is copied
30Mechanism of Replication Takes place in the nucleusDNA untwists & both strands are replicated almost simultaneously50 bases /sec are addedThe parent DNA strands serve as a template for making a new strand
31DNA polymerase unzips the 2 strands Each strand is used as a templateFree nucleotides present in the nucleus, pair with the exposed basesA with T, G with CAs bases pair DNA Ligase an enzyme links the phosphate of each nucleotide to the sugar of the previous onePairing & bonding continue till 2 new strands are formed.
32Enzyme works from 5’3’Synthesis is anti parallel 5’3’ and 3’5’As bases pair DNA Ligase an enzyme links the phosphate of each nucleotide to the sugar of the previous onePairing & bonding continue till 2 new strands are formed.