© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 1 The Search for Genetic Material Early geneticists didn’t know what the genetic material was, what carried genes The genetic material needed to:  Contain information  Be able to be copied easily  Be variable to account for diversity

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 2 Was it DNA or Protein? Geneticists thought that Chromosomes might carry the genes (from mitosis)  Composed of DNA and protein Which is the genetic material?  Protein is large, complex and stores info  DNA seemed too small and simple

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 3 Griffith’s Experiment Two strains of bacteria  R – harmless (1)  S – deadly (2) Heat killed Strain S is also harmless (3) Something from heat killed Strain S makes Strain R deadly (4)

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 4 Avery, MacLeod, and McCarty Isolated compounds from Strain S Added these to Strain R DNA transformed Strain R into Strain S Proved DNA was the genetic material

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 5 DNA, Genes, & Chromosomes Inside a cell, we have chromosomes Each chromosome is made up of one molecule of DNA and many proteins Along the DNA are regions that code for information (genes) Animation of this relationship Animation

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 6 Watson & Crick Determined the 3-D structure of DNA  Structure revealed its function X-ray crystallographic studies showed that  Double helix  Ladder twisted into a spiral coil

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 7 The Double Helix Two long strands of nucleotides Sugar-phosphate backbone Base-pairing holds the strands together

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 8 Base-Pairing Rules Strands held together by base-pairing  Hydrogen bonds between bases Strict base-pairing rules:  A binds to T  G binds to C Makes copying the sequence possible

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 9 Fulfills Three Requirements Contains info of the genetic material  Sequence of bases stores this info Easily copied  Each strand is a template for the other Accounts for diversity  Alleles have different DNA sequences

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 10 Individuals have slight differences in sequence Different species have greater differences Variation & Diversity Person 1 Person 2 Chicken

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 11 DNA Replication DNA Synthesis during S- phase of Interphase H-bonds between 2 strands are broken Two Strands separate Each strand is a template for the other

DNA Synthesis & Replication: DNA “unzips” Two opposite strands separate Matching bases are added to each side Result: Two copies of the original DNA molecule

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 13 Many enzymes and proteins are involved  Initiate replication  Unwind the DNA -helicase  Stabilize the open strands  Add & connect bases to form backbone (DNA polymerases) Enzymes also needed to correct mistakes Mistakes result in mutation DNA Replication

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 14 Two Types of Mutations Base Changes  A change in the sequence of nucleotide bases  Most are silent (do not change a protein) Chromosomal Abnormalities (macro- mutations)  Large changes in whole regions of DNA  Most are lethal

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 15 Base Mutations Incorrect base-pairings that are not fixed  Mutagens increase the frequency Next replication includes these changes Source of new alleles (new variation)  A few are beneficial (make a better protein)  Most are silent (make no change in a protein)  Some are harmful (most that change a protein)

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 16 Mutations Ask for examples of mutant human genes Bad mutations include ->  sickle cell anemia, hemophilia, color blindness. Can you find a mutation in this picture?mutation in this picture

Mutations There at least two mutations -> blue eyes, white skin (occurred long ago).

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 18 DNA Repair DNA polymerases often insert incorrect bases  DNA mismatch Proofreading enzymes correct mistakes

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 19 DNA Repair Enzymes recognize damaged DNA Cut the backbone on either side Damaged DNA is removed DNA is corrected

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 20 Inherited Repair Disorders Xeroderma pigmentosum

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 21 The Griffith experiment showed that A. Something heritable was being passed between the bacterial strains. B. DNA was the genetic material. C. Protein was the genetic material. D. Strain S was lethal to mice. Concept Quiz

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 22 Watson and Crick showed that A. A binds to T and G binds to C. B. One strand is a template for the other strand. C. The DNA molecule can be easily replicated. D. All of the above. Concept Quiz

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 23 DNA repair is A. Only important during replication. B. Found in some species. C. Vital to maintaining DNA’s integrity. D. An inherited disorder. Concept Quiz

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 24 Process Animation 12.1a DNA Repair: Mutations from DNA Replication  Macintosh Macintosh  Windows Windows

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 25 Process Animation 12.1b DNA Repair: Mutations from Sunlight  Macintosh Macintosh  Windows Windows