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DNA Replication:

DNA Replication 1

DNA Replication:

2 DNA Replication

Replication Facts:

3 Replication Facts DNA has to be copied before a cell divides DNA is copied during the S or synthesis phase of interphase New cells will need identical DNA strands

Synthesis Phase (S phase):

4 Synthesis Phase (S phase) S phase during interphase of the cell cycle Nucleus of eukaryotes Mitosis -prophase -metaphase -anaphase -telophase G 1 G 2 S phase interphase DNA replication takes place in the S phase.

DNA Replication:

5 DNA Replication Begins at Origins of Replication Two strands open forming Replication Forks (Y-shaped region) New strands grow at the forks Replication Fork Parental DNA Molecule 3’ 5’ 3’ 5’

DNA Replication:

6 DNA Replication As the 2 DNA strands open at the origin, Replication Bubbles form Prokaryotes (bacteria) have a single bubble Eukaryotic chromosomes have MANY bubbles Bubbles Bubbles

DNA Replication:

7 DNA Replication Enzyme Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds Single-Strand Binding Proteins attach and keep the 2 DNA strands separated and untwisted

DNA Replication:

8 DNA Replication Enzyme Topoisomerase attaches to the 2 forks of the bubble to relieve stress on the DNA molecule as it separates Enzyme DNA Enzyme

DNA Replication:

9 DNA Replication Before new DNA strands can form, there must be RNA primers present to start the addition of new nucleotides Primase is the enzyme that synthesizes the RNA Primer DNA polymerase can then add the new nucleotides

DNA Replication:

10 DNA Replication DNA polymerase can only add nucleotides to the 3’ end of the DNA This causes the NEW strand to be built in a 5’ to 3’ direction RNA Primer DNA Polymerase Nucleotide 5’ 5’ 3’ Direction of Replication

Remember HOW the Carbons Are Numbered!:

11 Remember HOW the Carbons Are Numbered! O O=P-O O Phosphate Group N Nitrogenous base (A, G, C, or T) CH2 O C 1 C 4 C 3 C 2 5 Sugar (deoxyribose)

Synthesis of the New DNA Strands:

12 Synthesis of the New DNA Strands The Leading Strand is synthesized as a single strand from the point of origin toward the opening replication fork RNA Primer DNA Polymerase Nucleotides 3’ 5’ 5’

Synthesis of the New DNA Strands:

13 Synthesis of the New DNA Strands The Lagging Strand is synthesized discontinuously against overall direction of replication This strand is made in MANY short segments It is replicated from the replication fork toward the origin Lagging Strand 5’ 5’ 3’ 3’

Proofreading New DNA:

14 Proofreading New DNA DNA polymerase initially makes about 1 in 10,000 base pairing errors Enzymes proofread and correct these mistakes The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors

Semiconservative Model of Replication:

15 Semiconservative Model of Replication Idea presented by Watson & Crick The two strands of the parental molecule separate, and each acts as a template for a new complementary strand New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA Parental DNA DNA Template New DNA

DNA Damage & Repair:

16 DNA Damage & Repair Chemicals & ultraviolet radiation damage the DNA in our body cells Cells must continuously repair DAMAGED DNA Excision repair occurs when any of over 50 repair enzymes remove damaged parts of DNA DNA polymerase and DNA ligase replace and bond the new nucleotides together

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17 Thank you

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