DNA: The Genetic Material 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 protein-destroying enzyme. The material was affected by DNA-destroying 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)