DNA Structure Unit 4

DNA Facts DNA DeoxyriboNucleic Acid Basis for all living things Foundation for all diversity & unity on Earth Every living thing has DNA. That means that you have something in common with a zebra, a tree, a mushroom and a beetle!!!! DNA is too small to see, but under a microscope it looks like a twisted up ladder!

History of DNA Frederick Griffith Discovers that a factor in diseased bacteria can transform harmless bacteria into deadly bacteria. (1928) Oswald Avery Expanded on Giffith’s experiment. (1944) Hershey & Chase Studied bacteriophages (viruses that kill bacteria). Helped determine if genes were made of DNA or proteins. (1952) Rosalind Franklin X-ray photo of DNA. (1952) Watson and Crick described the DNA molecule from Franklin’s X-ray.(1953)

Structure of DNA Nucleotide Small units that link together to form DNA Made of 3 parts Phosphate Group 5-C sugar molecule deoxyribose Nitrogen Base

Structure of DNA cntd. Nitrogen (N) base N base makes nucleotides different 4 bases Adenine (A) Guanine (G) Thymine (T) Cytosine (C) 2 main groups of bases Purines Double ring of C & N atoms Includes adenine and guanine Pyrimidines Single ring of C & N atoms Includes thymine and cytosine Base pairing rules Purines bind to pyrimidines Adenine binds to thymine Guanine binds to cytosine

Structure of DNA cntd. Double Helix Model created by James Watson & Francis Crick Structure of DNA “spiral staircase” made of 2 strands of nucleotides twisting around a central axis. Also known as a “twisted ladder” Sides of ladder are made of alternating sugar and phosphate units held together with a strong covalent bond Rungs are made up of a purine and a pyrimidine held together by a weak Hydrogen (H) bond. Base pairing results in a complementary strand (this is how DNA replicates)