The Search for Genetic Material Early geneticists didnt

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

Was it DNA or Protein? n Geneticists thought that Chromosomes might carry the genes (from mitosis) ¨ Composed n 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 2

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

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

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

Watson & Crick n Determined the 3 -D structure of DNA ¨ n 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 6

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

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

Fulfills Three Requirements n Contains info of the genetic material ¨ n Easily copied ¨ n Sequence of bases stores this info 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 9

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

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

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

DNA Replication n 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 n Mistakes result in mutation n © 2006 W. W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 13

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

Base Mutations n Incorrect base-pairings that are not fixed ¨ Mutagens increase the frequency n Next replication includes these changes n 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 15

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

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

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

DNA Repair n n 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 19

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

Concept Quiz 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. © 2006 W. W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 21

Concept Quiz 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. © 2006 W. W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 22

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

Process Animation 12. 1 a DNA Repair: Mutations from DNA Replication Macintosh Windows © 2006 W. W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 24

Process Animation 12. 1 b DNA Repair: Mutations from Sunlight Macintosh Windows © 2006 W. W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e 25