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Transcript
Chapter 9 DNA: The Genetic Material Sections 1-3 • Section 1- Identifying the Genetic Material • Section 2- The Structure of DNA • Section 3- The Replication of DNA A Brief Review • Chromosomes consist of 2 replicated strands of DNA tightly coiled around proteins. The 2 strands (chromatids) are attached at the centromere. • Gene is a segment of DNA that codes for proteins or RNA molecule • Cell’s DNA is copied during synthesis (S) • Mutations occur when chromosomes break, causing the broken piece to detach or reattach somewhere else Identifying Genetic Material • Fredrick Griffith(1928) studied bacteria. Used vaccine to kill pneumonia. (mice) • Vaccine- substance that is prepared from dead or weakened disease-causing agents. • Discovered transformation change in genotype caused when cells take up foreign genetic material. Avery’s Experiments • Oswald Avery 1944 • The material responsible for for transformation is not affected by proteindestroying enzyme. • The material was affected by DNAdestroying enzyme. • This concluded that DNA is the material responsible for transformation. • Explained why harmless R bacterial changed and became virulent S bacteria and killed mouse. Viral Genes and DNA • Hershey and Chase used viruses, which were composed of DNA or RNA surrounded by a protein coat. • Bacteriophage- virus that infects bacteria bacteria cell produced more viruses. • Found that DNA of viruses was injected into the bacterial cells, the injected DNA molecule causes bacterial cells to produce more viral DNA and proteins. This proved that DNA, not proteins, was the hereditary material in cells. The Structure of DNA • Watson and Crick pieced together a model of the structure of DNA. • Double helix- 2 strands twisted around each other (staircase) • Each strand was made of nucleotides. (subunits of DNA) Nucleotide • Each nucleotide is made of 3 parts. – A phosphate group – A five carbon sugar • deoxyribose – A nitrogen containing base • Adenine ( A) Guanine (G) • Thymine (T) Cytosine (C) Pairing Between Bases • The double helix is held together by weak hydrogen bonds between the pair of bases. • Base pairing rules- Adenine pairs with Thymine (A-T) Cytosine pairs with Guanine (C-G) • The sequence of bases on one strand determines the sequence of bases on the other strand. The Replication of DNA DNA Replication • DNA copy is made during synthesis. (S) • Step 1- double helix unwinds (DNA helicases enzymes break hydrogen bonds) • Step 2- DNA polymerases enzymes move along each strand of DNA. Polymerases add nucleotides to the exposed nitrogen base. • Step 3- DNA polymerase adds nucleotides to all of the DNA until entire strand is copied. (2 identical strands are produced) • DNA polymerase also “proof-read” to reduce errors. (1 error per 1 billion nucleotide)