Molecular Genetics

1. Molecular Genetics Chapter 12 Honors Biology Mrs. Stewart, Rm 806

2. Experiments Showed that DNA is the Genetic Material • In 1928, Frederick Griffith reported studies on a species of bacterium. He studied two varieties of a bacterium, a pathogenic strand and a variant, that was harmless • A transformation occurred which means that one strain of bacteria was transformed into another one

3. Griffith’s Experiment

4. Transformation

5. Oswald Avery, Colin MacLeod, Maclyn McCarty

6. Avery, McCarty, and Macleod • Repeated Griffith’s experiment and used the heat-killed bacteria and made a juice or extract from it • Added enzymes to the juice that would break down lipids, proteins, and carbohydrates, and RNA • Transformation occurred in all of these except when tested using DNA

7. Avery, McCarty, and MacLeod’s Experiment

8. Bacteriophage • Is a virus that infects a bacterium • Stages of infection • Attachment • Entry or injection • Replication • Assembly • Lysing of the cell

9. Lytic Cycle of Viral Infection

10. Alfred Hershey and Martha Chase • Were interested in knowing which part of the virus infected the bacterium • They labeled two batches of viruses with radioactive sulfur-35 and phosphorus-32 • The protein was labeled with S-35 and the DNA core with P-32 • The viruses’ DNA entered the bacteria, and the protein coat remained outside the bacteria

11. Hershey and Chase’s Experiment

12. Base Pairing Charts • DNA to DNA A-T T-A C-G G-C DNA to RNA A-U T-A C-G G-C • RNA to RNA A-U U-A C-G G-C

14. DNA Replication • The process by which DNA duplicates itself • Unzipping occurs when the hydrogen bonds between the base pairs are broken and the two strands unwind. Each of the separated strands serves as a template for the attachment of complementary bases • DNA helicase unzips the original strand • DNA polymerase base pairs free nucleotides to the original strand • DNA ligase ties the strand back together

15. Replication

16. Transcription • RNA Polymerase attaches to special places on the DNA molecule, separates the two strands, and synthesizes a mRNA • mRNA is complementary to one of the DNA strands • The base pairing mechanism ensures that mRNA will be a complementary copy of the DNA strand that serves as its template

17. Transcription: Prokaryote • RNA Polymeraseunwinds and unzips DNA • Complementary NTP’s (nucleoside triphosphates) add to template • DNA strand from 5’ to 3’ • RNA Polymerase begins transcribing the DNA at a specific point • RNA strand is identical to the non- coded DNA (and complementary to the template strand)

18. Transcription

19. Translation (Protein Synthesis) • The two subunits of the ribosome bind to a molecule of mRNA • The initiator codon, AUG, binds to the first anticodon of tRNA, signaling the beginning of a polypeptide chain • Soon the anticodon of another tRNA binds to the next mRNA codon • This tRNA carries the 2nd amino acid that will be placed into the chain of the polypeptide

20. Translation Continued • A peptide bond (covalent bond) forms between two amino acids • This polypeptide chain continues to grow until the ribosome reaches a stop codon of mRNA • Once here, the new polypeptide and mRNA are released from the ribosome

21. Translation of mRNA

22. Makin' Proteins So proteins are determined by the chain of amino acids that make them up But how do our protein makers know which amino acids to add?

23. The Actors:

24. The Play:

25. The Overview