Biology 212 General Genetics Fall 2006


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Biology 212 General Genetics Fall 2006

  1. 1. Biology 212 General Genetics Fall 2006 Lecture 1 "DNA" • Introductions • Class Roster • Handout: Course syllabus • Review of syllabus: content  Main topics: Classical (Mendelian) Genetics, Molecular Genetics, Human Genetics, Population Genetics Genetics: The study of genes, the individual units of heredity Genes: Segments of DNA that contain the information for a protein or RNA product Molecular 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 pea o Developed concept that heredity is determined by discrete units o Traits can be dominant or recessive Human genetics: Examined through pedigree analysis (genetic family trees), karyotype (chromosome) analysis, human genome project, DNA testing Population genetics: Inheritance in groups of interbreeding organisms. Relevant for conservation biology, forensics. • Review of syllabus course requirements  Course objectives  Textbook  Problem assignments  Grading Reading: Text Chapter 1 pp. 2-9 Lecture Outline: 1. DNA is the genetic material a. Transformation experiments b. Phage experiments 2. Chemical structure of DNA 3. DNA structure suits its function 1
  2. 2. Lecture Notes: 1. DNA is the molecule of heredity: Experimental evidence 1869 Friedrich Miescher o discovered DNA (deoxyribonucleic acid) o DNA is abundant in cell nuclei o DNA is a weak acid Late nineteenth century o Male and female reproductive cells fuse in fertilization o Discovery of chromosomes o Chromosomes are closely associated with DNA 1928 Frederick Griffith o Demonstrated bacterial transformation; bacteria can be converted from a non- virulent to a virulent strain by injection of a substance. Fig. 1.2 S=smooth strain, causes pneumonia in mouse R=rough strain, non-virulent Heat-killed S cells + living R cells à inject into mouse; causes pneumonia 1944 Oswald Avery, Colin Macleod, Maclyn McCarty o Showed that the transforming substance was DNA. Fig. 1.3 DNA from S cells + R cells à produce S cells Therefore the substance responsible for genetic transformation is DNA. DNA is the genetic material. 1952 Alfred Hershey, Martha Chase o Demonstrated that transmission of information from one generation to another relies on DNA. Viruses: • Structure 2
  3. 3. o DNA or RNA (genetic material) o Protein coat and tail fibers • Parasites that require host cell to reproduce Fig. 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 bacteria Results: • 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 DNA Could 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 Crick o Developed a 3D-structural model of DNA structure, the "DNA double helix". Critical features of the model: • DNA is made of nucleotides o Sugar o Phosphate o 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 bonds o A pairs with T o C pairs with G • The bases that pair are said to be complementary • The order of the bases on DNA comprises the information 3
  4. 4. • 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 helix 3. 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 a new partner strand. • DNA synthesis carried out by enzyme, DNA polymerase Fig. 1.7 Parental DNA=template 5' 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 5' 4