Discovering the Genetic Material DNA Experiments Discovering the Genetic Material

Learning Targets “I Can…” -Summarize the experiments of Griffith, Avery, Hershey and Chase and their conclusions about the genetic material in cells. -Define “transformation.” -Describe a bacteriophage. -Summarize the contributions of Franklin, Chargaff, and Watson and Crick.

Frederick Griffith’s Experiment Griffith was the first to show that the genetic material can be taken up by a cell; this is now called bacteria transformation(1928) How did he do this?

Oswald Avery’s Experiment Avery discovered that DNA was responsible for transforming cells (1944) How did he do it?

Hershey-Chase Experiment Hershey and Chase discovered that DNA was the genetics material in ALL types of cells How did they do it?

What is the role of DNA in heredity? Storing Copying Transmitting

What is DNA made of? Long chains of nucleotides How do we know this? Chargaff’s Rule Franklin’s Xrays Watson and Crick’s models

Chargaff’s Rule

Rosalind Franklin’s X-Rays Her experiments showed that… DNA is twisted like the coils of a spring DNA may have two strands The nitrogen bases are near the center of DNA

James Watson and Francis Crick With the help of Franklin’s x-rays, they built the first model of DNA that showed two strands of nucleotide sequences wound around each other.

What does the double helix model tell us about the structure of DNA? 1. Antiparallel strands 2. Hydrogen Bonding 3. Base Pairing: explains Chargaff’s Rule

Antiparallel Strands DNA is always read in the 5’ to 3’ direction

Hydrogen Bonding

Base Pairing

How is DNA copied? Complementarity DNA Polymerase: an enzyme that joins individual nucleotides to produce a new strand of DNA

How is DNA copied? Complementarity Replication Forks

How is DNA copied? Complementarity Telomeres/Telomerase: telomeres are the tips of chromosomes where replication is difficult. An enzyme called telomerase adds short, repeated DNA sequences to prevent genes from being damaged or lost during replication. Telomerase is especially important in rapidly dividing cells, such as stem cells or embryonic cells.

How is DNA copied?

Prokaryotic Versus Eukaryotic Replication Prokaryotic: starts at a single point, proceeds in both direction Eukaryotic: starts at several points, proceeds in both directions

Prokaryotic Versus Eukaryotic Replication

References www.Quia.com http://www.visionlearning.com/en/library/Biology/2/DNA-I/149 http://study.com/academy/lesson/oswald-avery-experiment-discovery-quiz.html http://en.wikipedia.org/wiki/Hershey%E2%80%93Chase_experiment http://biology.clc.uc.edu/courses/bio104/hershey-chase%20js.htm