1. Chromosomes and DNA Replication

2. Prokaryotes and Eukaryotes Prokaryotes: Prokaryotes: –lack nuclei –lack many organelles –DNA located in cytoplasm –single circular DNA chromosome Eukaryotes: Eukaryotes: –1000x DNA than prokaryotes –DNA located in cell nucleus in chromosomes –chromosome numbers vary  Drosophila-8  Human- 46

3. DNA is REALLY long Prokaryote: like fitting 300m rope into backpack Prokaryote: like fitting 300m rope into backpack Eukaryote: nucleus of a human cell has 1 meter of DNA Eukaryote: nucleus of a human cell has 1 meter of DNA How? How? CHROMOSOMES! CHROMOSOMES!

4. Chromosome Structure Chromatin- substance composed of DNA & protein Chromatin- substance composed of DNA & protein Histones- proteins that DNA is tightly wrapped around Histones- proteins that DNA is tightly wrapped around Chromatin + Histones = nucleosome (bead-like structures) Chromatin + Histones = nucleosome (bead-like structures) Nucleosomes Nucleosomes –pack to form a thick fiber shorten with coils and loops –able to fold enormous amounts of DNA –little change over evolution

5. How does DNA exist? Most of the time dispersed in nucleus so individual chromosomes not visible Most of the time dispersed in nucleus so individual chromosomes not visible When do we see chromsomes? When do we see chromsomes? During mitosis During mitosis

6. DNA Replication DNA = two strands DNA = two strands –both can be used for replication Prokaryotes: begins at single point in chromosome and continues in both directions Prokaryotes: begins at single point in chromosome and continues in both directions Eukaryotes: begins at hundred of points and continues until completely replicated Eukaryotes: begins at hundred of points and continues until completely replicated Replication forks- sites of separation and replication Replication forks- sites of separation and replication

7. Duplicating DNA Replication- DNA duplicates before cell division Replication- DNA duplicates before cell division DNA separates into 2 strands DNA separates into 2 strands Each strand acts as template Each strand acts as template Two new complementary strands follow base pairing rules Two new complementary strands follow base pairing rules

8. Replication Two replication forks Two replication forks New bases are added according to base pairing rules New bases are added according to base pairing rules –What would be added to original strand of ATTGAC? Each new strand has one original strand of bases and one strand of newly added bases Each new strand has one original strand of bases and one strand of newly added bases

9. Replication Process Helicase “unzips” DNA by breaking hydrogen bonds Helicase “unzips” DNA by breaking hydrogen bonds DNA strands unwind and act as templates DNA strands unwind and act as templates DNA polymerase join individual nucleotides to produce DNA molecule (usually a polymer) & “proofreads” new DNA strand DNA polymerase join individual nucleotides to produce DNA molecule (usually a polymer) & “proofreads” new DNA strand How is this “proofreading” helpful? How is this “proofreading” helpful?

10. Let’s put it all together http://www.youtube.com/watch?v=4jtmO ZaIvS0&feature=related http://www.youtube.com/watch?v=4jtmO ZaIvS0&feature=related