1. DNA DeoxyriboNucleic Acid

2. What can DNA do? Carries information from one generation to the next Determines the heritable characteristics of organisms Genes must be easily copied

3. DNA Structure DNA is a long molecule made up of units called –Nucleotides 3 basic components –5-carbon sugar »Deoxyribose –Phosphate group –Nitrogenous base

4. Nitrogenous Bases There are four Nitrogenous Bases –Purines: Two rings in their structures Adenine Guanine –Pyrimidines: One ring in their structure Cytosine Thymine

5. Backbone of DNA Formed by sugar and phosphate groups of each nucleotide The nitrogenous bases stick out sideways from the chain Nucleotides can be joined together in any order –Any sequence is possible!!

6. Chargaff’s Rules Adenine always pairs with Thymine Cytosine always pairs with Guanine

7. Double Helix Rosalind Franklin –Used X-ray diffraction –Had the evidence that the double helix existed but didn’t put it all together Watson and Crick –Tried to put together a model of DNA –Wasn’t until they saw Franklin’s X-rays that they discovered the double helix pattern

8. Double Helix cont. Looks like a twisted ladder Hydrogen bonds between certain nitrogenous bases provide the force to keep the structure together Hydrogen bonds can only form between certain base pairs –Adenine and thymine –Guanine and cytosine –Proves Chargaff’s rules