1. INTERACTIVE NOTES PGS. 295-299 12-2 CHROMOSOMES & DNA REPLICATION

2. LOOKING BACK… Prokaryotes DNA in the cytoplasm Single large DNA molecule, called a chromosome Eukaryotes 1000x amount of DNA as prokaryotes Many chromosomes in the nucleus

3. CHROMOSOME STRUCTURE The nucleus of a human cell must fit more than 1 meter of DNA! Chromatin = DNA + Protein packed together Chromatin is coiled around proteins, called histones

4. EUKARYOTIC CHROMOSOME STRUCTURE

5. DNA REPLICATION Replication is the copying process to duplicate DNA (before cell division) DNA strands are complementary to each other Replication fork = where separation and replication occur The DNA molecule separates and the original strand serves as a template or parent strand Two new complementary (daughter) strands are formed

6. Example: If the template strand has the sequence TACGTT What would be the sequence of the complementary DNA strand that forms during replication? Remember: Adenine (A) pairs with thymine (T) Guanine (G) pairs with cytosine (C) Answer: ATGCAA

7. MECHANISM OF DNA REPLICATION Many enzymes are involved in DNA replication DNA Helicase : Unzips the DNA strands Key Enzyme: DNA POLYMERASE Adds new nucleotides Proofreads each new DNA strand

8. OTHER IMPORTANT PROTEINS SSB or Single-Stranded binding protein Binds to single strand DNA and prevents it from reforming a double helix DNA Primase Synthesizes short RNA primers Becomes a target for new DNA synthesis DNA ligase Binds all of the new strand pieces together

9. THREE STEPS IN DNA REPLICATION Unwinding DNA Helicase unwinds and separates the parent strands Complimentary Base Pairing DNA is synthesized in the 5’ to 3’ direction Leading strand: synthesis is easier (it is in 5’ to 3’ direction for new strand) Lagging strand: not oriented in 5’ to 3’ direction Creates Okazaki fragments joined by DNA ligase Joining DNA polymerase binds short RNA sequences together Results in two identical Semi-conservative double helix molecules One old strand and one new strand

10. REPLICATION IN ACTION… https://www.youtube.com/watch?v=zdDkiRw1PdU

11. Copyright Pearson Prentice Hall Nitrogen Bases Replication Fork DNA Polymerase Replication Fork Original strand New Strand Growth