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Animations/websites

Animations/websites

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Animations/websites

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  1. Animations/websites • http://www.wiley.com/college/pratt/0471393878/student/animations/dna_replication/index.html • http://www.nobelprize.org/educational/medicine/dna_double_helix/

  2. DNA replication

  3. DNA length • DNA molecules are very long • Example: E. coli bacteria- 4,639,221 base pairs • In order to fit in side of the nucleus of a cell the DNA must be folded very small • A human cell contain 100 times the b.p. found in bacteria (3.2 billion b.p.)

  4. Chromosome Structure • The nucleus of a cell contains more then 1 meter of DNA • What is a chromosome made up of? Review! • Chromosomes contain both DNA and protein • Protein= histones

  5. Chromosome Structure • DNA + Histone protein= Nucleosome • Nucleosomes pack together to further condense

  6. Location of Replication • Where is DNA stored in the cell? • Can DNA leave the nucleus? (why?) • DNA replication takes place inside of the Nucleus • Why does DNA need to Replicate? • When does DNA replicate? • Replication takes place before cell division

  7. DNA Replication • DNA is copied to make 2 identical DNA strands • Each strand of the original double-stranded DNA molecule serves as template for the production (semi-conservative)

  8. How it works • DNA replication is carried out by a series of Enzymes

  9. Steps to replicationStep 1 • The DNA molecule is unwound and prepared for synthesis by helicase (replication fork) • Helicase- separates DNA strand

  10. Step 2-Single- stranded Binding proteins • Single-stranded binding proteins (SSB)- keeps strands apart during replication

  11. Steps to replication • Elongation- different for each side of the DNA strand

  12. DNA directionality Review! • The strands are oriented in opposite directions. • This is the only way the bases can line up to form the hydrogen bonds

  13. 5’  3’ 5’3’ refers to the order of the carbons in the deoxyribose sugar

  14. 5’  3’ strandStep 3 A • Called the leading strand • RNA primase adds primer • DNA polymerase can “read” the template • continuously add nucleotides (into fork) • Nucleotides are added according to the base pairing rule

  15. DNA Polymerase • DNA polymerase moves along the template strand in a 3'-5' direction • daughter strand is formed in a 5'-3' direction. • Nucleotides are added according to the base pairing rule

  16. 3’ to 5’ strandStep 3B • The new strand is called the lagging strand • Cannot be read by DNA polymerase (oriented in the opposite direction) Replication takes place AWAY from fork

  17. Lagging Strand • RNA Primase reads the sequence and adds primer • DNA polymerase lengthens the segment • Formation of Okazaki fragments • Helicase unzips more of the strand

  18. Okazaki fragment

  19. Lagging Strand • DNA ligase connects the fragments together

  20. DNA polymerase proofreads as it adds nucleotides

  21. “Key players” • DNA polymerase- adds new nucleotides • RNA primase- starts replication on upside down strand • DNA ligase- connects new fragments on upside down strand