DNA: The Genetic Material Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Hammerling Experiment Cells of green algae cut into pieces and observed to see which were able to express heredity information. Discovered heredity information stored in the foot of the cell. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Transplantation Experiments Very early it was discovered chromosomes were composed of proteins and DNA. But it took several experiments to conclusively determine specifically which substance made up genes. Griffith Experiment Documented movement of genes from one organism to another (transformation). Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Avery and Hershey-Chase Experiments Avery Experiment Removed almost all protein from bacteria, and found no reduction in transforming activity. Hershey-Chase Used radioactive isotopes to label DNA and protein. Found genes used to specify new generations of viruses were made of DNA.

Chemical Nature of Nucleic Acids DNA made up of nucleic acids. Five carbon sugar, phosphate group, and an organic base. Purines - Large bases Adenine and Guanine Pyrimidines - Small bases Cytosine and Thymine Chargaff’s Rule A =T and G=C Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Fig. 14.7

Chemical Nature of Nucleic Acids Nucleotide made up of a sugar attached to a phosphate and a base. Nucleotides distinguished by the bases. Reaction between phosphate group of one nucleotide and hydroxl group of another is dehydration synthesis. Phosphodiester Bond 3-5 phosphodiester bond Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Three-Dimensional Structure of DNA X-ray diffraction suggested DNA had helical shape with a diameter of about 2 nanometers. Watson and Crick deduced DNA is a double helix with bases of two strands pointing inward forming base-pairs. Purines pairing with pyrimidines. Constant 2 nanometer diameter. Strands are antiparallel.

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Semi-Conservative Replication Each chain in the helix is a complimentary mirror image of the other. Double helix unzips and undergoes semi-conservative replication. Each strand of the original duplex becomes one strand of another duplex. Confirmed by Meselson-Stahl Experiment. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Replication Process Replication of DNA begins at one or more sites on the DNA molecule where there is a specific sequence of nucleotides called a replication origin. DNA replicating enzyme DNA polymerase III and other enzymes add nucleotides to the growing complementary DNA strands. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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Fig. 14.15

RNA polymerase (primase) constructs an RNA primer. Replication Process DNA polymerase cannot link the first nucleotides in a newly synthesized strand. RNA polymerase (primase) constructs an RNA primer. DNA polymerase adds nucleotides to 3’ end. Leading strand replicates toward replication fork. Lagging strand elongates from replication fork. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

DNA Replication Fork Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

DNA ligase attaches fragment to lagging strand. Replication Process DNA ligase attaches fragment to lagging strand. Because synthesis of the leading strand is continuous, while the lagging strand is discontinuous, the overall replication of DNA is referred to as semidiscontinuous. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Opening DNA Double Helix Initiating replication Unwinding duplex Replication Process Opening DNA Double Helix Initiating replication Unwinding duplex Stabilizing single strands Relieving torque Building a Primer Assembling Complementary Strands Removing the Primer Joining Okazaki Fragments Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Eukaryotic Replication In Eukaryotic cells, DNA is packaged in nucleosomes within chromosomes. Each individual zone replicates as a discrete section called a replication unit or a replicon. Each replication unit has its own origin of replication. Fast Replication Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

One-Gene/One-Polypeptide Hypothesis Genes produce their effects by specifying the structure of enzymes. Each gene encodes the structure of one enzyme. Many enzymes contain multiple polypeptide subunits, each encoded by a separate gene. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Pivotal Genetic Experiments Chemical Nature of Nucleic Acids Review Pivotal Genetic Experiments Chemical Nature of Nucleic Acids Three-Dimensional Structure of DNA Replication Semi Conservative Eukaryotic DNA Replication One-Gene/One-Polypeptide Hypothesis Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies