DNA History and Structure

The year is 1928. Frederick Griffith tries to determine why certain bacteria give people pneumonia. He figures out something is able to be passed from harmful bacteria to harmless ones, making them DEADLY. Discovery: Genetic information could be transferred from one bacteria to another. This is called transformation. Help the students realize that if the info was transferred, it must have been encoded in a molecule… something that can be passed between bacteria, but that doesn’t disappear when a bacteria dies.

The year is 1944. Oswald Avery repeats the experiments that Griffith did. He is trying to figure out which molecule was transforming the harmless bacteria into killers. He uses enzymes to break down different molecules. When he breaks down DNA, the harmless bacteria stay harmless. What does this tell us about DNA?

Discovery: DNA stores and transmits the genetic information from one generation of an organism to the next!!! http://images.google.com/imgres?imgurl=http://history.nih.gov/exhibits/nirenberg/images/photos/03_avery_pu.jpg&imgrefurl=http://history.nih.gov/exhibits/nirenberg/popup_htm/03_avery.htm&usg=__uPC1lBxN5_NBP0TT8Jn5GTDDrvw=&h=474&w=400&sz=25&hl=en&start=4&sig2=pdW5KbqlxdhVf9SRnuzlJQ&um=1&tbnid=s7sYET9WC2CenM:&tbnh=129&tbnw=109&prev=/images%3Fq%3Doswald%2Bavery%26hl%3Den%26rlz%3D1C1CHMB_enUS354US354%26um%3D1&ei=gcVZS7v4IdOKlAfay_37BA !

It is now 1952. Alfred Hershey and Martha Chase are busy studying viruses called bacteriophages. (they infect bacteria!) They knew viruses infect cells by injecting their own genetic material inside, but what is the genetic material? Hershey and Chase radioactively marked the viral DNA. When the viruses infected bacteria, they saw that the bacteria now contained radioactive material. What could Hershey and Chase deduce from these results?

That’s two experiments that say DNA is the genetic material!!! Discovery: DNA is the genetic material of the viruses, not the protein coat! That’s two experiments that say DNA is the genetic material!!! http://images.google.com/imgres?imgurl=http://www.uic.edu/classes/bios/bios100/summer2003/Chase__Hershey_1953.jpg&imgrefurl=http://www.uic.edu/classes/bios/bios100/summer2003/chase.htm&usg=__qY4gUAjql5DiSVyA8wgGYAXjMUM=&h=475&w=600&sz=69&hl=en&start=2&sig2=q2B9onCV47MP7OGlP8ZYxg&um=1&tbnid=UxBVRrr0p4QaJM:&tbnh=107&tbnw=135&prev=/images%3Fq%3Dhershey%2Bchase%26hl%3Den%26rlz%3D1C1CHMB_enUS354US354%26sa%3DN%26um%3D1&ei=1MlZS-LEF-H8lAeBvvSOBQ

DNA = DeoxyriboNucleic Acid So what is DNA, anyway? DNA = DeoxyriboNucleic Acid Long molecule made up of units called nucleotides https://www.edulink.networcs.net/sites/teachlearn/science/Image%20Library/dna.jpg

5-carbon sugar (deoxyribose) 3 Basic Parts of DNA: 5-carbon sugar (deoxyribose) A phosphate group Nitrogenous base

Who figured out the structure of DNA? Chargaff’s Rule: A=T and C=G Erwin Chargaff’s discovered that the percentage of adenine present in DNA is the same as the percentage of thymine. Also, the percentages of cytosine and guanine are equal to one another. http://history.nih.gov/exhibits/nirenberg/images/photos/03_chargaff_pu2.jpg Chargaff’s Rule: A=T and C=G

Rosalind Franklin is using X-rays to study the structure of DNA. It’s 1952 Rosalind Franklin is using X-rays to study the structure of DNA. http://www.chem-is-try.org/wp-content/uploads/2009/03/rosalind-franklin.jpg

DNA Franklin’s X-ray pictures show a pattern that suggests two strands of DNA coiled around one another in a helix and that the nitrogenous bases are near the center of the molecule .

Should we give some credit to Ros? Meanwhile, Francis Crick and James Watson are building 3D models of DNA using wire and cardboard. They are stumped until they see a copy of Rosalind Franklin’s X-ray picture. Nah. She’s just a woman…

DNA is located in the nucleus. Where is it found? DNA is tightly coiled up around histone proteins so that it can all fit in the nucleus. The coiled DNA is called chromatin. DNA is located in the nucleus. During mitosis, the DNA is duplicated and the chromatin condenses into chromosomes.

Watson and Crick Watson and Crick immediately figure out that the DNA molecule has to be a double-helix with two strands of DNA coiled around one another, nitrogenous bases facing inward, paired according to Chargaff’s Rule.

This is why replication can occur! DNA is made up of two complementary strands. Remember, the base pairing rules! Due to specific base pairing, if you know the sequence of one strand, you can figure out the sequence of the other! This is why replication can occur!