DNA and Replication copyright cmassengale 1 DNA Structure

  • Slides: 33
Download presentation
DNA and Replication copyright cmassengale 1

DNA and Replication copyright cmassengale 1

DNA Structure Continued copyright cmassengale 2

DNA Structure Continued copyright cmassengale 2

copyright cmassengale 3

copyright cmassengale 3

Antiparallel Strands • One strand of DNA goes from 5’ to 3’ • The

Antiparallel Strands • One strand of DNA goes from 5’ to 3’ • The other strand is opposite in direction going 3’ to 5’ copyright cmassengale 4

P 5 DNA O 3 3 P 5 O O C G 1 P

P 5 DNA O 3 3 P 5 O O C G 1 P 5 3 2 4 4 P 5 P 2 3 1 O T A 3 O 3 5 O copyright cmassengale 5 P P 5

Question: • If there is 30% Adenine, Adenine how much Cytosine is present? copyright

Question: • If there is 30% Adenine, Adenine how much Cytosine is present? copyright cmassengale 6

Answer: • There would be 20% Cytosine • Adenine (30%) = Thymine (30%) •

Answer: • There would be 20% Cytosine • Adenine (30%) = Thymine (30%) • Guanine (20%) = Cytosine (20%) • Therefore, 60% A-T and 40% C -G copyright cmassengale 7

History of DNA copyright cmassengale 8

History of DNA copyright cmassengale 8

History of DNA • Early scientists thought protein was the cell’s genetic material because

History of DNA • Early scientists thought protein was the cell’s genetic material because it was more complex than DNA copyright cmassengale 9

Griffith Experiment copyright cmassengale 10

Griffith Experiment copyright cmassengale 10

Transformation • Fred Griffith worked with virulent S and nonvirulent R strain Pneumoccocus bacteria

Transformation • Fred Griffith worked with virulent S and nonvirulent R strain Pneumoccocus bacteria • He found that R strain could become virulent when it took in DNA from heat-killed S strain • Study suggested that DNA was probably the genetic material copyright cmassengale 11

DNA Structure • Rosalind Franklin took diffraction x-ray photographs of DNA crystals • In

DNA Structure • Rosalind Franklin took diffraction x-ray photographs of DNA crystals • In the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays copyright cmassengale 12

Rosalind Franklin copyright cmassengale 13

Rosalind Franklin copyright cmassengale 13

DNA Replication copyright cmassengale 14

DNA Replication copyright cmassengale 14

DNA replication overview copyright cmassengale 15

DNA replication overview copyright cmassengale 15

Replication Facts • DNA has to be copied before a cell divides • DNA

Replication Facts • DNA has to be copied before a cell divides • DNA is copied during the S phase of interphase S • New cells will need phase • identical DNA G 1 G 2 • strands Mitosis copyright cmassengale 16

DNA Replication • Begins at Origins of Replication • Two strands open forming Replication

DNA Replication • Begins at Origins of Replication • Two strands open forming Replication Forks (Y-shaped region) • New strands grow at the forks 5’ Parental DNA Molecule 3’ copyright cmassengale 3’ Replication Fork 17 5’

DNA Replication • DNA replications is Semiconservative. • Each new double-stranded DNA contains one

DNA Replication • DNA replications is Semiconservative. • Each new double-stranded DNA contains one old strand (template) and one newly-synthesized complementary strand copyright cmassengale 18

DNA Replication • As the 2 DNA strands open at the origin, Replication Bubbles

DNA Replication • As the 2 DNA strands open at the origin, Replication Bubbles form • Chromosomes have MANY bubbles Bubbles copyright cmassengale 19

DNA Replication Enzymes • Helicase-unwinds and separates the 2 DNA strands by breaking the

DNA Replication Enzymes • 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 copyright cmassengale 20

DNA Replication Enzymes • Topoisomerase attaches to DNA ahead of the bubble to relieve

DNA Replication Enzymes • Topoisomerase attaches to DNA ahead of the bubble to relieve stress on the DNA molecule as it separates. Video Enzyme DNA copyright cmassengale 21

DNA Replication • Before new DNA strands can form, there must be RNA primers

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 III can then add the new nucleotides copyright cmassengale 22

DNA Replication • DNA polymerase can only add nucleotides to the 3’ end of

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 5’ 3’ Nucleotide DNA Polymerase Direction of Replication copyright cmassengale RNA Primer 23 5’

Synthesis of the New DNA Strands • The Leading Strand is synthesized as a

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 5’ 3’ Nucleotides DNA Polymerase copyright cmassengale 5’ RNA Primer 24

Synthesis of the New DNA Strands • The Lagging Strand is synthesized discontinuously against

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 Leading Strand 5’ 3’ DNA Polymerase 5’ 3’ Lagging Strand RNA Primer copyright cmassengale 3’ 5’ 25

Lagging Strand Segments • Okazaki Fragments - series of short segments on the lagging

Lagging Strand Segments • Okazaki Fragments - series of short segments on the lagging strand • Must be joined together by an enzyme DNA Okazaki Fragment RNA Primer 5’ 3’ Polymerase 3’ 5’ Lagging Strand copyright cmassengale 26

Joining of Okazaki Fragments • The enzyme Ligase joins the Okazaki fragments together to

Joining of Okazaki Fragments • The enzyme Ligase joins the Okazaki fragments together to make one strand DNA ligase 5’ 3’ Okazaki Fragment 1 Okazaki Fragment 2 3’ 5’ Lagging Strand copyright cmassengale 27

Replication of Strands Replication Fork Point of Origin copyright cmassengale 28

Replication of Strands Replication Fork Point of Origin copyright cmassengale 28

Proofreading New DNA • DNA polymerase initially makes about 1 in 10, 000 base

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 copyright cmassengale 29

DNA Damage & Repair • Chemicals & ultraviolet radiation damage the DNA in our

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 copyright cmassengale 30

Question: • What would be the complementary DNA strand for the following DNA sequence?

Question: • What would be the complementary DNA strand for the following DNA sequence? DNA 5’-CGTATG-3’ copyright cmassengale 31

Answer: DNA 5’-CGTATG-3’ 3’-GCATAC-5’ copyright cmassengale 32

Answer: DNA 5’-CGTATG-3’ 3’-GCATAC-5’ copyright cmassengale 32

copyright cmassengale 33

copyright cmassengale 33