LECTURE CONNECTIONS 10 | DNA: The Chemical Nature of the Gene © 2009 W. H. Freeman and Company

10.2 All Genetic Information Is Encoded in the Structure of DNA or RNA Early Studies of DNA showed that - the physical basis of hereditary lies in the nucleus; - DNA contains 4 nitrogenous bases: A, C, G and T; - DNA consists of a large number of linked, repeating untis, called nucleotides; - Nucleotides contain a sugar, a phosphate and a base; - Chargaff’s rule: the amount of A=T and the amount of C=G.

DNA as the Source of Genetic Information The discovery of the transforming principle: Dr. Griffith’s experiment with Streptococcus pneumonia The Hershey–Chase experiment (Figure 10.5) 10.2 All Genetic Information Is Encoded in the Structure of DNA or RNA

DNA as the source of Genetic Information Watson and Crick’s discovery of the three- dimensional structure of DNA X-ray diffraction image of DNA 10.2 All Genetic Information Is Encoded in the Structure of DNA or RNA

RNA as the Source of Genetic Information - Few viruses such as the tobacco mosaic virus (TMV). - TMV: single molecule of RNA surrounded by a helically arranged cylinder of protein molecules

10.3 DNA Consists of Two Complementary and Antiparallel Nucleotide Strands That Form a Double Helix Primary structure of DNA refers to its nucleotide structure and how the nucleotides are joined together. Secondary structure of DNA refers to DNA’s stable tree-dimensional configuration. Tertiary structure of DNA are complex packing arrangements of dsDNA in chromosomes (Chapter 11)

The sugar of nuclei acids have 5 carbon atoms (pentoses). DNA sugar (deoxyribose) and a hydrogen atom (-H) at the 2’- carbon atom. Nitrogenous bases: purines (six-sided ring attached to a five sided ring -A and G); pyrimidines (six-sided ring only, C and T or U) Phosphate: phosphorus atom bounded to 4 oxygen atoms

10.3 DNA Consists of Two Complementary and Antiparallel Nucleotide Strands That Form a Double Helix Secondary structure of DNA The double helix Hydrogen bond and base pairing Antiparallel complementary DNA strands

10.3 DNA Consists of Two Complementary and Antiparallel Nucleotide Strands That Form a Double Helix Secondary structure of DNA Different secondary structures

10.4 Special Structure Can Form in DNA and RNA Hairpin structure: In single strands of nucleotides, when sequences of nucleotides on the same strand are inverted complements, a hairpin structure will be formed.

10.4 Special Structure Can Form in DNA and RNA Inverted Repeats: in double-stranded DNA, sequences that are inverted replicas of each other Palindrome: If an inverted repeat is also complementary to itself, then it is called a palindrome. Cruciform: A hairpin forms within each of the two single-stranded sequences, which makes a cruciform.