1. DNA Structure and Replication

2. What does this cartoon mean?

3. DNA (Deoxyribonucleic acid) DNA carries all of an organism’s hereditary (genetic) information It is the “universal language” of all organisms! Controls the production of proteins Found in the nucleus of the cell (eukaryotes) or floating in cytoplasm (prokaryotes ONLY!) Belongs to a chemical group of compounds called nucleic acids

4. Structure of DNA DNA is made up of a long chain of nucleotides. Each nucleotide has three parts. a phosphate group a deoxyribose sugar a nitrogen-containing base phosphate group deoxyribose (sugar) nitrogen-containing base

5. The nitrogen containing bases are the only difference in the four nucleotides.

6. Watson and Crick determined the three-dimensional structure of DNA by building models. They realized that DNA is a double helix that is made up of a sugar- phosphate backbone on the outside with bases on the inside.

7. What pattern do you see between the nitrogen bases?

8. Watson and Crick’s discovery built on the work of Rosalind Franklin and Erwin Chargaff. –Franklin’s x-ray images suggested that DNA was a double helix of even width. –Chargaff’s rules stated that A=T and C=G.

9. What would be their corresponding strands? 1) ATCGATCCG 2)GATCCGATC

10. DNA’s shape is a double helix “Twisted Ladder” Sugar-Phosphate backbone “outside of the ladder” Held together by covalent bonds Nitrogen base pairs in center “rungs of the ladder” Held together by hydrogen bonds (weak!)

13. DNA Replication DNA replicates before cell division (mitosis and meiosis) to ensure that each new cell receives the correct number of chromosomes.

14. DNA replicates like a zipper. It unzips to replicate. Step 1: Original DNA splits in half (“unzips”) Step 2: 2 new strands are copied Step 3: End result is 2 identical DNA molecules

15. DNA Replication is semiconservative 2 new molecules are called “daughters” Semiconservative: half of the daughter strand is NEW DNA, and half of the daughter is the ORIGINAL (old) DNA REPLICATION MAKES 2 EXACT COPIES!