DNA as genetic material Structure of DNA DNA

- DNA as genetic material - Structure of DNA - DNA replication Sections 8. 1, 8. 2, and 8. 3

What is this stuff?

DNA!!! ▪ Deoxyribonucleic Acid ▪ Consists of 4 bases – Adenine – Thymine – Guanine – Cytosine

Frederick Griffith ▪ Did experiments with 2 different types of pneumonia ▪ Smooth vs. rough – Smooth covered in with sugars – Rough does not have this covering

His experiment

Why did this happen? ▪ Some sort of material must have transferred between the live R and the heat killed S – Did not know it was DNA just yet ▪ Called the mystery material “transforming principle”

Oswald Avery ▪ Worked on extending Griffiths work – 10 years!!! ▪ Combined lived R bacteria with extract from S bacteria – Were able to directly observe the change of R bacteria into S

Avery’s experiments ▪ Qualitative tests – Chemical tests showed there was actually NO proteins present. Only DNA ▪ Chemical analysis – These show the amounts or proportions of elements found in DNA. Proteins hardly contain phosphorus ▪ Enzyme tests – Enzymes known to break down proteins and RNA did nothing to stop the transformation. Only enzymes that broke down DNA stopped the process

Hershey and Chase ▪ Confirmed DNA as genetic material in 1952 ▪ Studied viruses that infected bacteria – Bacteriophages ▪ Take over a bacterial cell to make more bacteriophages – Very simple things ▪ A small amount of DNA covered by a protein coat

Bacteriophages!!!

How do they work?

Their experiments ▪ Experiment 1 – Tagged radioactive sulfur atoms on phage’s protein molecules – Let phages infect bacteria – Studied bacteria after they were infected – Found very little radioactivity present in bacteria ▪ Proteins WERE NOT passed to the bacteria from the bacteriophages

Their experiments ▪ Experiment 2 – Tagged phosphorus molecules in the phage’s DNA with radioactivity – Let phages infect bacteria – Studied bacteria after they were infected – Found A LOT of radioactivity within the bacteria ▪ DNA was passed to bacteria. More phages are made within the bacteria. ▪ Increased phages = increased radioactive tags

DNA structure ▪ Consists of 4 bases or nucleotides ▪ 2 parts to the “backbone” – 1 phosphate group – Ring-ring shaped sugar ▪ deoxyribose

Base pairing rules ▪ Adenine always pairs with Thymine – Double ring with double ring ▪ Guanine always pairs with Cytosine – Single ring with single ring ▪ A=T and C=G – Chargaff’s rule

Base pairing practice ▪ GTA ▪ CTTGAC ▪ GATTACA ▪ TTGGACCGGAT

Watson and Crick ▪ Got credit for the shape of DNA – Used an image they were not supposed to have – Stolen from Rosalind Franklin ▪ They waited until she died before submitting their results to be published ▪ Ended up winning the Nobel Prize ▪ She got no posthumous credit for “their” work

Split into 2 groups