Unit 4 – Part 1

 DNA  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!

 Frederick Griffith  Discovers that a factor in diseased bacteria can transform harmless bacteria into deadly bacteria (1928)  Rosalind Franklin  X-ray photo of DNA. (1952)  Watson and Crick  described the DNA molecule from Franklin’s X- ray.(1953)

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

 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

 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)