Chapter – DNA and How Genes Work

1920’s – Griffith’s experiments on transformation 1940’s - Avery, MacLeod and McCarty demonstrated that transforming agent was DNA 1952 – Hershey and Chase – definitive evidence that DNA is hereditary material 1953 – Watson and Crick AND Franklin DNA is the genetic material

Griffith experiment S strain - pathogenic R strain - non-pathogenic Streptococcus pneumoniae Frederick Griffith (1879 – 1941)

Griffith experiment

Hereditary information can pass between cells = transformation Griffith experiment conclusion

What is transforming agent? DNA or protein? Avery, MacLeod and McCarty

DNA carries the heritable information Avery, MacLeod and McCarty conclusion 1944

Hershey and Chase Martha Cowles Chase Alfred Day Hershey

Hershey and Chase Bacteriophage: viruses that infect bacterial cells

Hershey and Chase

Genetic material in virus was DNA DNA is agent of heredity Hershey and Chase conclusion INDEPENDENT FUNCTIONS OF VIRAL PROTEIN AND NUCLEIC ACID IN GROWTH OF BACTERIOPHAGE* B~ A. D. HERSHEY AND MARTHA CHASE (From the Department of Genetics, Carnegie Institution of Washington, Cold Spring Harbor, Long Island) (Received for publication, April 9, 1952) The work of Doermaml (1948), Doermann and Dissosway (1949), and Anderson and Doermann (1952) has shown that bacteriophages T2, T3, and T4 multiply in the bacterial cell in a non-infective form. The same is true of the phage carried by certain lysogenic bacteria (Lwoff and Gutmann, 1950). Little else is known about the vegetative phase of these viruses. The experiments reported in this paper show that one of the first steps in the growth of T2 is the release from its protein coat of the nucleic acid of the virus particle, after which the bulk of the sulfur-containing protein has no further function.

DNA – just what is it?

Nucleic Acids Monomers = nucleotides Polymer = DNA, RNA

DNA Nucleotide (monomer) 4 bases

Bases Purines: Aand G Pyrimidines: T and C (and U in RNA)

The proportion of A always equals T and G always equals C. A=T and G=C Also A+G = C+T Chargaff's rules

Rosalind Franklin ( ) X-ray crystalography

Structure of DNA Watson and Crick 1953

Watson and Crick (1953)

Replication Expression DNA Structure

*Double helix *Complementarity *Antiparallel DNA Structure

Double helix

Antiparallel

Base pairing in DNA Complementarity Purines always pair with pyrimidines

Complementarity A always with T G always with C

DNA Replication

DNA “double helix”

DNA “double helix” A - T G - C

How does replication occur?

Conservative Model

Semi-conservative Model

Dispersive Model

DNA Replication

Semiconservative replication

Meselson-Stahl experiment

DNA replication occurs in semiconservative manner Meselson-Stahl experiment THE REPLICATION OF DNA IN ESCHERICHIA COLI* BY MATTHEW MESELSON AND FRANKLIN W. STAHL GATES AND CRELLIN LABORATORIES OF CHEMISTRY, t AND NORMAN W. CHURCH LABORATORY OF CHEMICAL BIOLOGY, CALIFORNIA INSTITUTE OF TECHNOLOGY, PASADENA, CALIFORNIA Communicated by Max Delbrick, May 14, 1958 Introduction.-Studies of bacterial transformation and bacteriaphage infection'-‘ strongly indicate that deoxyribonucleic acid (DNA) can carry and transmit hereditary information and can direct its own replication. Hypotheses for the mechanism of DNA replication differ in the predictions they make concerning the distribution among progeny molecules of atoms derived from parental molecules.6 Radioisotopic labels have been employed in experiments bearing on the distribution of parental atoms among progeny molecules in several organisms.6-9 We anticipated that a label which imparts to the DNA molecule an increased density might permit an analysis of this distribution by sedimentation techniques. To this end, a method was developed for the detection of small density differences 1958

DNA Replication

Expression DNA

Information stored in order of the bases

+/ copies

Central Dogma of Cell Biology DNA (gene) Protein

GENETICS: TA TUM AND BEADLE GENETIC CONTROL OF BIOCHEMICAL REACTIONS IN NEUROSPORA: AN "AMINOBENZOICLESS" MUTANT* By E. L. TATUM AND G. W. BEADLE DEPARTMENT OF BIOLOGY, STANFORD UNIVERSITY Communicated April 17, 1942 Para-aminobenzoic acid has recently been recognized as a factor required for the growth of a number of micro6rganisms' and as a member of the vitamin B group.2 One of the number of x-ray induced mutants of Neurospora crassa, obtained as described elsewhere,' is characterized by the loss of ability to synthesize p-aminobenzoic acid. This "aminobenzoicless“ mutant is differentiated from normal by a single gene, is unable to grow on unsupplemented synthetic medium, but its growth is indistinguishable from normal when p-aminobenzoic acid is supplied. Each gene codes for a specific and unique protein 1958 – Nobel Prize One-Gene/One-Polypeptide Hypothesis

Central dogma of molecular biology

Extracting and using the information Two Steps: 1. 2.

Extracting and using the information The information

Extracting and using the information An intermediate

Extracting and using the information The product

Translation – constructing a protein DNA mRNA protein transcription translation

Transcription DNA copied into mRNA

mRNA single-stranded U instead of T

Translation – constructing a protein DNA mRNA protein transcription translation

Instructions are coded in the order of the bases

20 amino acids Protein is a polymer of amino acids Instructions are an ordered list of amino acids in protein

Each ‘word’ in the DNA-RNA vocabulary is 3 ‘letters’ long One “word”

Each ‘word’ in the DNA-RNA vocabulary is 3 ‘letters’ long A ‘word’ is called a codon

Triplet Codon: group of 3 bases that specifies an amino acid

The Genetic Code -Redundant -Not ambiguous -Stop codons -AUG - start -Universal (nearly) Marshal W. Nirenberg

Universal (nearly)

The Dictionary

Punch tape

Ribosome mRNA tRNA

tRNA brings in the amino acides

Translation

Universal (nearly)

Reading frames

the red dog ate the bug Reading frames her edd oga tet heb ug