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What does DNA look like? Inherited characteristics are determined by genes. Genes are passed on to offspring Genes are part of chromosomes DNA = Deoxyribonucleic Acid Pieces of the Puzzles Material that make up genes have to be able to do two things: 1. Give instructions to the cell for building and maintaining 2. Be able to be copied when the cell divides Nucleotides: the Subunits of DNA Nucleotides have three parts: sugar, phosphate and nitrogen base The sugar is deoxyribose The nitrogen base is the nucleic acid part There are FOUR nitrogen bases: Adenine (A), Thymine (T), Guanine (G) and Cytosine (C) FIGURE ONE p144. Chargaff’s Rules Erwin Chargaff found that the amount of adenine equals the amount of thymine And the amount of cytosine = the amount of guanine Franklin’s Discovery Rosalind Franklin took x-ray pictures of DNA and determined that DNA has a spiral shape Watson and Crick’s Model Used Frankin’s data to help determine that DNA is like a twisted ladder. Built models of DNA DNA’s Double Structure Shape of DNA is known as a double helix The two sides of the ladder are made of alternating sugars and phosphates. The steps or rungs of the ladder are made up of pairs of nitrogen bases. Chargaff’s data helped to show that A always pairs with T and G always pairs with C on the DNA steps. (Remember: I like to eat AT Golden Corral.) FIGURE 4 page 146 Making copies of DNA The base pairs allow the cell to copy or replicate the DNA. Bases are complementary (A only pairs with T, C only pairs with G). How copies are made 1. The DNA molecule splits down the middle (unzips down the center of each base pair step). 2. The bases on each side are a pattern to rebuild a new complementary strand. Two DNA strands are formed from one. Each is made of half “old” DNA and half “new” DNA When copies are made Every time a cell divides, DNA gets copied. Happens in interphase. See page 147 FIGURE 5