David Sadava H Craig Heller Gordon H Orians

David Sadava H. Craig Heller Gordon H. Orians William K. Purves David M. Hillis Biologia. blu B – Le basi molecolari della vita e dell’evoluzione The Chemistry of Life

The Chemistry of Life • What is the evidence that the gene is DNA? • What is the structure of DNA? • How is DNA replicated? • How are errors in DNA repaired?

The Chemistry of Life - What is the evidence that the gene is DNA?

The Chemistry of Life - What is the evidence that the gene is DNA?

The Chemistry of Life - What is the evidence that the gene is DNA?

The Chemistry of Life - What is the evidence that the gene is DNA? Bacteriophage T 2: reproduction cycle

The Chemistry of Life - What is the evidence that the gene is DNA?

The Chemistry of Life - What is the evidence that the gene is DNA?

The Chemistry of Life - What is the structure of DNA? The structure of DNA was determined using many lines of evidence. One crucial piece came from the X-ray crystallography data obtained by Rosalind Franklin. A purified substance can be made to form crystals; position of atoms is inferred by the pattern of diffraction of Xrays passed through it.

The Chemistry of Life - What is the structure of DNA? X-Ray diffraction apparatus (A) and Rosalind Franklin (B)

The Chemistry of Life - What is the structure of DNA? Chemical composition also provided clues that DNA is a polymer of nucleotides: deoxyribose, a phosphate group, and a nitrogen-containing base. The bases: • purines - adenine (A), guanine (G); • pyrimidines - cytosine (C), thymine (T).

The Chemistry of Life - What is the structure of DNA? Nucleotides have three components

The Chemistry of Life - What is the structure of DNA? X-ray crystallography convinced them the molecule was helical. Other evidence suggested there were two polynucleotide chains that ran in opposite directions—antiparallel. In 1953 Watson and Crick established the general structure of DNA.

The Chemistry of Life - What is the structure of DNA? James D. Watson and Francis Crick with a double helix DNA molecule model, Cavendish Laboratories 1953

The Chemistry of Life - What is the structure of DNA? DNA molecule is a double helix

The Chemistry of Life - What is the structure of DNA? Base pairing in DNA is complementary (part 1)

The Chemistry of Life - What is the structure of DNA? Base pairing in DNA is complementary (part 2)

The Chemistry of Life - What is the structure of DNA? Functions of DNA: • store genetic material—millions of nucleotides; base sequence stores and encodes huge amounts of information; • susceptible to mutation—change in information.

The Chemistry of Life - What is the structure of DNA? Three possible replication patterns: A) semiconservative replication; B) conservative replication; C) dispersive replication.

The Chemistry of Life - How is DNA replicated? Three patterns for DNA replication

The Chemistry of Life - How is DNA replicated? DNA polymerase binds to the template strand (part 1)

The Chemistry of Life - How is DNA replicated? DNA polymerase binds to the template strand (part 2)

The Chemistry of Life - How is DNA replicated? No DNA forms without a primer

The Chemistry of Life - How is DNA replicated? Many proteins collaborate in the replication complex

The Chemistry of Life - How are errors in DNA repaired? DNA repair mechanisms