1 / 43

CHAPTER 29

CHAPTER 29. DNA: Genetic Information, Recombination, and Mutation to accompany Biochemistry, 2/e by Reginald Garrett and Charles Grisham.

nowles
Télécharger la présentation

CHAPTER 29

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CHAPTER 29 DNA: Genetic Information, Recombination, and Mutation to accompany Biochemistry, 2/e by Reginald Garrett and Charles Grisham All rights reserved. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt Brace & Company, 6277 Sea Harbor Drive, Orlando, Florida 32887-6777

  2. Outline • 29.1 DNA Carries Genetic Information • 29.2 Genetic Information in Bacteria • 29.3 Molecular Mechanism of Recombination • 29.4 The Immunoglobulin Genes • 29.5 Molecular Nature of Mutation • 29.6 RNA as Genetic Material • 29.7 Transgenic Animals

  3. The Transforming Principle is DNA • Griffith in 1928 injected bacteria into mice • Combination of heat-killed type S and non-virulent type R killed the mice • Showed that type S had been transformed by the type R! • In 1944, Oswald Avery showed that the active transforming agent was DNA!

  4. Further Proof • In 1952, Hershey and Chase, studying bacteriophages, labelled DNA with 32P and protein with 35S • Bacteriophage progeny produced by infection of bacteria contained 32P (thus DNA from the original phage), but not 35S (from the protein)!

  5. Genetic Information Can Be Transferred Between Bacteria • In 1946, Lederberg and Tatum showed that two different strains of bacteria with different growth requirements could exchange genes • Lederberg and Tatum surmised that the bacterial cells must interact with each other - the process is now known as sexual conjugation

  6. Chromosome Mappingby Interrupted Mating • Passage of the ‘F factor’ from Hfr cells to F- cells also brings adjacent genes • Genes from the Hfr chromosome are transferred in a fixed order • This order can be mapped by ‘interrupted mating’ methods • The genetic map obtained reveals a circular arrangement of genes

  7. Mechanism of Recombination • General recombination: any pair of homologous DNA segments as substrates • In 1964, Robin Holliday proposed a model involving single-stranded nicks at homologous sites • Duplex unwinding, strand invasion and ligation create a Holliday junction

  8. Enzymology of Recombination • RecBCD initiates recombination in E.coli • RecA forms nucleoprotein filament for strand invasion and homologous pairing • RuvA, RuvB, RuvC drive branch migration and process the Holliday junction into recombination products • Eukaryotic systems are probably similar

  9. The RecA Protein • 38 kD enzyme that catalyzes ATP-dependent DNA strand exchange, leading to formation of Holliday junction • RecA forms a helical filament with a groove to accommodate DNA • RecA:ssDNA complex binds dsDNA at secondary site and searches for regions homologous with the bound ssDNA, then forms the desired duplex

  10. Resolving Holliday Junctions • Ruv proteins resolve the junction into recombination products • RuvA and RuvB act as a helicase that dissociates the RecA filament and catalyzes branch migration • RuvC is an endonuclease that binds at the junction and cuts pairs of DNA strands of similar polarity. Splice and patch recombinants result.

  11. Transposons • In 1950, Barbara McClintock showed that activator genes in corn could move freely about the genome. • This was at first viewed as heresy and McClintock was ostracized • Molecular biologists in the late 1970s rediscovered what McClintock knew • She received a MacArthur Award in 1981 and a Nobel in 1983

  12. Immunoglobulin Genes • Immunoglobulin genes maximize protein diversity with a limited amount of genetic information • DNA rearrangement (genetic recombination) during assembly of IG genes accounts for this diversity • Three separate genes are combined to form the L-chain gene • Four genes combine to form H-gene

  13. Molecular Nature of Mutation • Point mutations - one base for another - arise from mispairing, insertion of analogs or chemical mutagens • Mutagens include nitrous acid, hydroxylamine and alkylating agents • Insertions and deletions result in frameshift mutations

  14. PrionsProteins as Genetic Agents? • Prions are ‘protein infectious particles’ • Agents composed only of protein • Responsible for kuru, Creutzfeld-Jacob disease, mad-cow disease, etc. • The ‘infection’ appears to involve a change of secondary structure and conformation (or conformations!) in the prion protein • A Nobel for Stanley Prusiner in 1997

  15. Transgenic Animals • Genes can be introduced into animals by transfection - injection of plasmid DNA into recipient cells • Plasmids can be injected into fertilized eggs in mice • Expression is usually variable, because the gene is inserted randomly • Growth hormone transfection produces mice that are very large!

More Related