Biology 212 General Genetics Spring 2007Lecture 1 "DNA"- Introductions- Class Roster- Handout: Course syllabus- Review of syllabus: content Main topics: Classical (Mendelian) Genetics, Molecular Genetics, HumanGenetics, Population GeneticsGenetics: The study of genes, the individual units of heredityGenes: Segments of DNA that contain the information for a protein or RNA productMolecular genetics vs. classical genetics- Molecular genetics examines the chemical nature of genes.o The molecule DNA contains information for our traits.- Classical or Mendelian genetics is based on the experiments of Gregor Mendel (1860's) with the garden peao Developed concept that heredity is determined by discrete unitso Traits can be dominant or recessiveHuman genetics: Examined through pedigree analysis (genetic family trees), karyotype (chromosome) analysis, human genome project, DNA testingPopulation genetics: Inheritance in groups of interbreeding organisms. Relevant for conservation biology, forensics.- Review of syllabus course requirements Course objectives Textbook Problem assignments GradingReading: Text Chapter 1 pp. 2-9Lecture Outline:1. DNA is the genetic materiala. Transformation experimentsb. Phage experiments2. Chemical structure of DNA3. DNA structure suits its function1Lecture Notes:1. DNA is the molecule of heredity: Experimental evidence1869 Friedrich Mieschero discovered DNA (deoxyribonucleic acid)o DNA is abundant in cell nucleio DNA is a weak acidLate nineteenth centuryo Male and female reproductive cells fuse in fertilizationo Discovery of chromosomeso Chromosomes are closely associated with DNA1928 Frederick Griffitho Demonstrated bacterial transformation; bacteria can be converted from a non-virulent to a virulent strain by injection of a substance.Fig. 1.2S=smooth strain, causes pneumonia in mouseR=rough strain, non-virulentHeat-killed S cells + living R cells à inject into mouse; causes pneumonia1944 Oswald Avery, Colin Macleod, Maclyn McCartyo Showed that the transforming substance was DNA.Fig. 1.3DNA from S cells + R cells à produce S cellsTherefore the substance responsible for genetic transformation is DNA.DNA is the genetic material.1952 Alfred Hershey, Martha Chaseo Demonstrated that transmission of information from one generation to anotherrelies on DNA. Viruses:- Structure 2o DNA or RNA (genetic material)o Protein coat and tail fibers- Parasites that require host cell to reproduceFig. 1. 4 The Hershey-Chase Experiment- T2 virus is a bacteriophage, virus that infects bacteria- Can "tag" DNA or protein parts of T2 virus- Tag DNA of virus with radioactive phosphorus- Infect E. coli bacteria with tagged virus particles- Allow reproduction of virus and lysis of bacteriaResults: - The bacteria release progeny viruses tagged on their DNA. - When viral proteins were similarly tagged, the released progeny viruses do not have tagged proteins.2. The chemical structure of DNACould the molecular structure of DNA help answer- How genetic material is duplicated?- How DNA controls traits?- What happens when a mutation occurs on the DNA?1953 James Watson, Francis Cricko Developed a 3D-structural model of DNA structure, the "DNA double helix".Critical features of the model:- DNA is made of nucleotideso Sugaro Phosphateo Nitrogenous bases (Fig. 6.2) A=adenine C=cytosine G=guanine T=thymine- Nucleotides are linked together in long chains (Fig. 6.4)- Sugars and phosphates form the backbone- Bases occur in the interior- Bases form hydrogen bondso A pairs with To C pairs with G- The bases that pair are said to be complementary- The order of the bases on DNA comprises the information3- Two strands of DNA are antiparallel à the chains point in opposite directions 5'à 3'- The two paired strands coil around each other in a double helix3. Knowledge of the structure of DNA helps understand its function- Each strand provides information for synthesis of a complementary strand.- DNA contains information as a linear code: the order of the bases.- Changes in the DNA (mutations) can occur from errors in copying.DNA Replication- Process of copying the DNA. Each parental DNA strand directs the synthesis of anew partner strand.- DNA synthesis carried out by enzyme, DNA polymeraseFig. 1.7Parental DNA=template5' A T G C C G T A 3'3' T A C G G C A T 5' daughter DNAs 5' A T G C C G T A 3' 5' A T G C C G T A 3' 3' T A C G G C A T 5' 3' T A C G G C A T