The Molecular Basis of Inheritance Chapter 16 The Molecular Basis of Inheritance

Searching for Genetic Material, I Mendel: modes of heredity in pea plants Morgan: genes located on chromosomes Griffith: bacterial work Transformation: change genotype/phenotype by assimilating external substance Avery: transformation agent was DNA

Note: several animals were harmed in the making of this experiment Note: several animals were harmed in the making of this experiment. A moment of silence please (bioethics).

Searching for Genetic Material, II Hershey and Chase bacteriophages (phages) DNA, not protein, is the hereditary material Expt: sulfur(S) is in protein, phosphorus (P) is in DNA; only P was found in host cell Animation: Phage T2 Reproductive Cycle

Animation: DNA Double Helix DNA Structure Chargaff N base ratios A=T & C=G Watson & Crick (Wilkins, Franklin) Double Helix Nucleotides: nitrogenous base (ATCG) sugar (deoxyribose) phosphate group Animation: DNA Double Helix

Animation: DNA and RNA Structure DNA Bonding Purines: ‘A’ & ‘G’ Pyrimidines: ‘C’ & ‘T’ ‘A’ H bonds (2) with ‘T’ ‘C’ H bonds (3) with ‘G’ Animation: DNA and RNA Structure

Animation: DNA Replication Overview Watson & Crick strands are complementary; nucleotides line up on template according to base pair rules (Watson), Antiparralel (crick) Meselson & Stahl replication is semiconservative; Expt: varying densities of radioactive nitrogen New strands were half “heavy”, half “light” Animation: DNA Replication Overview

DNA Replication: a closer look Origin of replication (“bubbles”): beginning Replication fork: ‘Y’-shaped region where new DNA strands elongate Helicase: catalyzes untwisting DNA at replication fork DNA polymerase: catalyzes elongation of new DNA Animation: Origins of Replication

DNA Replication, II Antiparallel : sugar/phosphate backbone runs in opp. directions One runs 5’ to 3’, other runs 3’ to 5’ DNA polymerase only adds nucleotides at 3’ end DNA builds in 5’ to 3’ direction only

DNA Replication, III Leading strand: synthesis toward replication fork (5’ to 3’ direction from 3’ to 5’ template) Lagging strand: synthesis away from replication fork (Okazaki fragments); joined by DNA ligase (5’ to 3’ direction in pieces) Initiation: Primer (short RNA sequence w/primase enzyme) begins the replication process

DNA Repair Mismatch repair: DNA polymerase Excision repair: Nuclease Telomere ends: telomerase age

Enzymes and Proteins Review DNA Polymerase: elongate DNA, replace RNA primers, fix mistakes DNA Ligase: Joins Okazaki fragments together. Primase: Joins RNA nucleotides to make a primer. Helicases: Untwist double helix and separate the old strands. Single-strand Binding Proteins: hold separated strands apart. Nuclease: cuts out damaged DNA in an excision repair Telomerase: Catalyzes the lengthening of telomeres

Sugar-phosphate backbone Fig. 16-UN2 G C A T T A Nitrogenous bases G C Sugar-phosphate backbone C G A T C G Hydrogen bond T A

You should now be able to: Describe the contributions of the following people: Griffith; Avery, McCary, and MacLeod; Hershey and Chase; Chargaff; Watson and Crick; Franklin; Meselson and Stahl Describe the structure of DNA Describe the process of DNA replication; include the following terms: antiparallel structure, DNA polymerase, leading strand, lagging strand, Okazaki fragments, DNA ligase, primer, primase, helicase, topoisomerase, single-strand binding proteins Describe the function of telomeres Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings