DNA Structure AP Biology March 9/10, 2011 AP Biology March 9/10, 2011

objective SWBAT explain the key experiments in the discovery of DNA and the structure of DNA

Homework Complete DNA Replication interactive DNA Extraction pre-lab….see sheet Unit test: Cell Cycle and Division/DNA structure, function and replication…little on transpiration and Primary productivity Wed. 3-16

The History of DNA discovery

The Griffith experiment British microbiologist in 1928 Injected mice with Streptococcus pneumoniae Polysaccharide coat NO Polysaccharide coat

Griffith’s Findings Griffith found that transformation can occur the transfer of genetic material from one cell to another which can alter the genetic make-up Hereditary information can be passed from dead cells to living cells

The Oswald Avery experiment After Griffith’s experiments no one know what the transforming agent was In an effort to determine the transforming agent, Avery removed different biomolecules from the virulent strain, protein, polysaccharides, RNA and DNA and injected these into mice Proteins + Non- pathogenic  mice ok Polysaccharides + Non- pathogenic  mice ok RNA + Non – pathogenic.  mice ok DNA + Non – pathogenic  Mice died

Avery’s findings These experiments told Avery that DNA is the hereditary material in cells

Hershey-chase experiment Hershey and Chase labeled two parts of a bacteriophage (a virus that infects bacteria) cells with radioactive isotopes The protein coat The DNA The bacteria were allowed to reproduce The cells were agitated to see what tag would be found

Hershey-chase experiment

Hershey-chase findings DNA is the hereditary information that viruses released into the bacteria.

Rosalind Franklin Use x-ray crystallography to determine that DNA is a double helix This lead to the structure that Watson and Crick used

Watson and Crick DNA is double stranded DNA is a twisted helix that contains 200 base pairs in every rotation Complimentary base pairing Alternating sugar and phosphate backbone with a 3’ and 5’ end

The Structure of DNA

What is DNA made of? Many nucleotides make up DNA A nucleotide is composed of: Deoxyribose sugar Phosphate group 1 of 4 nitrogenous bases (being adenine, thymine, guanine and cytosine)

dna structure DNA is in the shape of a double helix The sides of the double helix, or backbone, are composed of the deoxyribose sugar and phosphate groups The rungs are composed of the bases matched up as complimentary base pairs The bases are held together by weak hydrogen bonds The DNA double helix is antiparallel: one side is 3’  5’ and the other side is 5’  3’ with nucleotides flipped over.

DNA Replication

Possible Ways to Replicate To explain heredity, biological information must be accurately copied and passed on to progeny There are 3 possible methods of DNA replication to consider In all 3 complimentary base pairing rules must be adhered to

Conservative Replication The original DNA model is intact with a completely new DNA strand being formed

Dispersive Replication 2 DNA strands are produced with sections of old and new DNA strands interspersed along each

Semiconservative Replication Strands are produced that each contain 1 old and 1 new DNA strand

Which model do you think it is?

DNA Replication is Semiconservative Each half of the DNA strand acts as a template Complimentary base pairs are added to create 2 full stands of DNA One side is the original DNA and the other is the newly generated DNA