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Chapter 10 The Molecular Basis of Inheritance The Molecular Basis of Inheritance
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codes for the Specific Sequence of Amino Acids in a Amino Acids determine the Protein’s Shape, which determine its Function. Proteins function as Biological Reactions Enzymes.
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The double helix
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Evidence of DNA Transformation - the process of transferring an inherited trait by an extract of DNA (Griffith) Mouse A is injected with live smooth pneumococcus He dies.
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Mouse B is injected with live rough pneumococcus. He lives. The smooth pneumococcus are heat-killed and injected into Mouse C. He lives
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Mouse D was injected with the mixture of heat-killed smooth pneumococcus and live rough pneumococcus. WHY? Transformation - transfer of genes from smooth to rough pneumonococcus
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Smooth pneumoncoccus are virulent. Hard to kill by immune response Presence of slime capsule Rough pneumococcus are nonvirulent. Can be destroyed by immune response No slime capsule Transformation
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Bacterial Transformation
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5th Hour’s Incredible Work!!! Class of 2003!
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5th Hour 2014
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STRUCTURE OF A VIRUS *Nucleic acid core of DNA or RNA *Capsid *Envelope *Extensions, filaments, or tail fibers *Bacteriophage
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Hershey and Chase used radioactive markers to label the protein and DNA in a bacteriophage. = protein = DNA Phages infect the bacteria
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Intracellular Extracellular
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Viruses infecting a bacterial cell Phage head Tail Tail fiber DNA Bacterial cell 100 nm
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Watson & Crick
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Base pairing in DNA H N H O CH 3 N N O N N N NH Sugar Adenine (A) Thymine (T) N N N N Sugar O H N H N H N O H H N Guanine (G) Cytosine (C)
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Using Franklin’s Data Purine + Purine: too wide Pyrimidine + pyrimidine: too narrow Purine + pyrimidine: width Consistent with X-ray data
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Rosalind Franklin and her X-ray diffraction photo of DNA (a) Rosalind Franklin Franklin’s X-ray diffraction Photograph of DNA (b)
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Complementary Base Pairing: Chargaff’s Rule AT C G A particular organism is 20% adenine then how much: T= C= G= 20% 30%
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The double helix
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A model for DNA replication: the basic concept (layer 4) (a) The parent molecule has two complementary strands of DNA. Each base is paired by hydrogen bonding with its specific partner, A with T and G with C. (b) The first step in replication is separation of the two DNA strands. (c) Each parental strand now serves as a template that determines the order of nucleotides along a new, complementary strand. (d) The nucleotides are connected to form the sugar-phosphate backbones of the new strands. Each “daughter” DNA molecule consists of one parental strand and one new strand. A C T A G A C T A G A C T A G A C T A G T G A T C T G A T C A C T A G A C T A G T G A T C T G A T C T G A T C T G A T C
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Helicase Single binding protein Replication Fork Topoisomerase
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Helicase RNA primer Polymerase III 3’ 5’ 3’ Polymerase I 5’ 3’ 5’ RNA Primase 5’ 3’ DNA Polymerase III attaches the nucleotides in a 5’ to 3’ direction only.
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3’ 5’3’ 5’ Polymerase III Okazaki Fragment Polymerase III DNA Ligase 3’ 5’ Polymerase I
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Which Model of Replication????
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 16.17 Nucleotide excision repair of DNA damage Nuclease DNA polymerase DNA ligase A thymine dimer distorts the DNA molecule. 1 Repair synthesis by a DNA polymerase fills in the missing nucleotides. 3 DNA ligase seals the Free end of the new DNA To the old DNA, making the strand complete. 4 A nuclease enzyme cuts the damaged DNA strand at two points and the damaged section is removed. 2
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 16.19 Telomeres 1 µm
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Enzymes Involved in DNA Replication Helicase - separates the two DNA strands by making a replication fork. DNA Polymerases (III and I) - binds the free nucleotides to the unzipped strand; replaces the RNA Primer with DNA nucleotides Single Binding Proteins – keeps the unzipped strands from tangling Topoisomerase – helps relive strain in helix RNA Primase – lays down the RNA primer Ligase – bonds Okazaki fragments after primer is removed
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Enzymes Involved in DNA Replication
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Blueprint for Proteins Proteins Function as Enzymes Enzymes make Chemical Rxns Go Thus! DNA is the Blueprint for life!!
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Avery’s Discovery of what molecule is responsible for Transformation
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 16.13 Incorporation of a nucleotide into a DNA strand New strandTemplate strand 5’ end 3’ end Sugar A T Base C G G C A C T P P P OH P P 5’ end 3’ end 5’ end A T C G G C A C T 3’ end Nucleoside triphosphate Pyrophosphate 2 P OH Phosphate
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DNA NUCLEOTIDE = Phosphate = Deoxyribose = Adenine = Guanine = Thymine = Cytosine PurinesPyrimidines
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