DISCOVERY OF DNA Chapter 12.1

Discovery of Genetic Material Scientists knew genetic information was carried on the chromosomes They did not know where on the chromosomes it was Two main parts of chromosomes are DNA and proteins

Frederick Griffith First main discovery of DNA as genetic material Working with two strains of Streptococcus pneumoniae he discovered that one strain could be transformed by the other Smooth strain (S) and rough strain (R)

Frederick Griffith Experiment 1 - Smooth killed the host (mouse) Experiment 2 -Rough did not kill the mouse Experiment 3 – heated smooth did not kill mouse Experiment 4- Mixture of heated smooth and rough killed mouse

Frederick Griffith

Oswald Avery Avery and colleagues identified the molecule that transformed the R strain into the S strain - not widely accepted Conclusion: In Griffith’s experiment when S cells were killed, they released DNA and the R cells incorporated it into their cells, changing the bacteria into S cells.

Alfred Hershey and Martha Chase Provided evidence that DNA was the transforming factor Used virus (bacteriophage) made of DNA and protein Viruses have to inject DNA into living material into a cell to reproduce

Alfred Hershey and Martha Chase Radioactive labeled the virus (bacteriophage) to see which part was injected into the bacteria Experiment 1 – radioactive label on the Protein coat of Virus. Experiment 2 – Radioactive label on the DNA of Virus

Alfred Hershey and Martha Chase NO protein transferred DNA is transferred

Copy the Questions to your notes! 1. What conclusion did Frederick Griffith make about bacteria? 2. What conclusion did Hershey and chase make about DNA? That one strain can be transformed by another The genetic material is in the DNA not the protein

STRUCTURE AND FUNCTION OF DNA Chapter 12.1

Humans share 50% of their DNA with bananas. Cells can contain 6-9 feet of DNA. If all the DNA in your body was put end to end, it would reach to the sun and back over 600 times. DNA in all humans is 99.9 percent identical. It is about one tenth of one percent that makes us all unique, or about 3 million nucleotides difference. In an average meal, you eat approximately 55,000,000 cells or between 63,000 to 93,000 miles of DNA. It would take a person typing 60 words per minute, eight hours a day, around 50 years to type the human genome.

What is DNA? P.A. Levene (1920’s)- Determined DNA is made up of 2 chains of nucleotides

Nucleotides Each nucleotide has 3 parts. 1. Deoxyribose sugar 2. Phosphate group 3. Nitrogenous base (4 types) Adenine (A) Guanine (G) Cytosine (C) Thymine (T)

Nucleotides Purines – Made up of two rings (A,G) Pyrimidines – made up of only one ring. (T,C)

Erwin Chargaff Analyzed the amounts of nitrogenous bases found in DNA Conclusion: the amount of adenine nearly is the same as the amount of thymine and the same for guanine and cytosine. C=G T=A

Erwin Chargaff Adenine=Thymine Cytosine=Guanine

Franklin and Wilkins Via the use of x-ray diffraction, Rosalind Franklin and Maurice Wilkins’ took this photo of DNA. Rosalind Franklin’s Photo 51

Watson and Crick DNA is a double helix structure. (Twisted ladder) 2 complementary paired strands of nucleotides twisted around each other. (rungs) Sugar and phosphate backbone (sides of ladder)

DNA Structure Cytosine (C) and guanine (G) bases pair to each other by 3 hydrogen bonds Thymine (T) and adenine (A) base pair to each other by 2 hydrogen bonds

Functions of DNA directs thecell to make specific proteins DNA directs the machinery of a cell to make specific proteins, and, therefore, DNA indirectly controls all of the functioning of all living things.

Functions of DNA DNA stores hereditary information of an individual

Functions of DNA has the ability to mutate EVOLUTION DNA has the ability to mutate (change). This allows for new characteristics and abilities to appear which may help an individual to survive and reproduce (EVOLUTION).

Functions of DNA DNA can replicate it’s self (Make copies)

Chromosomes and DNA DNA is organized into chromosomes DNA coils around proteins called histones (form nucleosomes) Nucleosome supercoil to make up DNA structure we know as a chromosome

If all organisms are made of the same 4 nucleotides in their DNA, how are they so different? Every organism has a different DNA sequence, which provides different information The more closely related two organisms are, the more similar their DNA nucleotide sequences will be.

Copy the questions to your notes! 1. The nitrogenous base Adenine (A) always bonds with ____ 2. The Nitrogenous base Cytosine (C) always bonds with ____ 3. Who discovered the structure of DNA? 4. DNA coils around proteins called _____________ T Histones Watson and Crick G