Chapter 12: Molecular Genetics

1. Chapter 12: Molecular Genetics • What You’ll Learn • How DNA was discovered to be the genetic material & know its structure • DNA replication • Protein synthesis • Gene regulation & mutations

2. Section 12.1: DNA: The Genetic Material • Section Objectives: • Summarize the experiments leading to the discovery of DNA as the gentic material • Analyze the structure of DNA • Describe the basic structure of the eukaryotic chromosome

3. What is DNA? • Although the environment influences how an organism develops, the genetic information that is held in the molecules of DNA ultimately determines an organism’s traits. • DNA achieves its control by determining the structure of proteins. • Within the structure of DNA is the information for life—the complete instructions for manufacturing all the proteins for an organism.

4. Bodies  Cells  DNA • Bodies are made up of cells • All cells run on a set of instructions spelled out in DNA

5. 1928 The “Transforming Principle” • Frederick Griffith • Streptococcus pneumonia bacteria • was working to find cure for pneumonia • harmless live bacteria (“rough”) mixed with heat-killed pathogenic bacteria (“smooth”) causes fatal disease in mice • a substance passed from dead bacteria to live bacteria to change their phenotype • “Transforming Principle”

6. The “Transforming Principle” mix heat-killed pathogenic & non-pathogenic bacteria live pathogenic strain of bacteria live non-pathogenic strain of bacteria heat-killed pathogenicbacteria A. B. D. C. mice die mice live mice live mice die Transformation=change in phenotype something in heat-killed bacteria could still transmit disease-causing properties

7. DNA is the “Transforming Principle” 1944 • Avery, McCarty & MacLeod • purified both DNA & proteins separately from Streptococcus pneumonia bacteria • which will transform non-pathogenic bacteria? • injected protein into bacteria • no effect • injected DNA into bacteria • transformed harmless bacteria into virulent bacteria mice die What’s the conclusion?

8. Confirmation of DNA 1952 | 1969 Hershey • Hershey & Chase • classic “blender” experiment • worked with bacteriophage • viruses that infect bacteria • grew phage viruses in 2 media, radioactively labeled with either • 35S in their proteins • 32P in their DNA • infected bacteria with labeled phages Why useSulfurvs.Phosphorus?

9. Hershey & Chase Protein coat labeled with 35S DNA labeled with 32P T2 bacteriophages are labeled with radioactive isotopes S vs. P bacteriophages infect bacterial cells bacterial cells are agitated to remove viral protein coats Which radioactive marker is found inside the cell? Which molecule carries viral genetic info? 32P radioactivity foundin the bacterial cells 35S radioactivity found in the medium

11. Blender experiment • Radioactive phage & bacteria in blender • 35S phage • radioactive proteins stayed in supernatant • therefore viral protein did NOT enter bacteria • 32P phage • radioactive DNA stayed in pellet • therefore viral DNA did enter bacteria • Confirmed DNA is “transforming factor” Taaa-Daaa!

12. Hershey & Chase 1952 | 1969 Hershey Martha Chase Alfred Hershey

13. The structure of nucleotides • DNA is a polymer made of repeating subunits called nucleotides.(the monomer) • Nucleotides have three parts: a simple sugar, a phosphate group, and a nitrogenous base. Nitrogenous base Phosphate group Sugar (deoxyribose)

14. The structure of nucleotides • in DNA there are four possible nucleotides, each containing one of these four bases. • The phosphate groups and deoxyribose molecules form the backbone of the chain, and the nitrogenous bases stick out like the teeth of a zipper. Nitrogenous base(A, G, C, or T) Phosphategroup Thymine (T) Nucleotide Sugar(deoxyribose) DNA nucleotide Sugar-phosphate backbone

15. Chargaff 1947 • DNA composition: “Chargaff’s rules” • varies from species to species • all 4 bases not in equal quantity • bases present in characteristic ratio • humans: A = 30.9% T = 29.4% G = 19.9% C = 19.8% RulesA = T C = G That’s interesting!What do you notice?

16. Paired bases • DNA structure • double helix • 2 sides like a ladder • Bases match together ( • A pairs with T • A : T • C pairs with G • C : G

17. 1953 | 1962 Structure of DNA • James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin and Maurice Wilkens Wilkins

18. Rosalind Franklin (1920-1958)

19. DNA is a double-stranded helix • Watson and Crick also proposed that DNA is shaped like a long zipper that is twisted into a coil like a spring. • Because DNA is composed of two strands twisted together, its shape is called double helix.

20. The structure of DNA Hydrogen bond Base pair Partial chemical structure Ribbon model Computer model

21. Anti-parallel strands • DNA molecule has “direction” • complementary strand runs in opposite direction 5 3 3 5

22. The importance of nucleotide sequences The sequence of nucleotides forms the unique genetic information of an organism. The closer the relationship is between two organisms, the more similar their DNA nucleotide sequences will be. • Scientists use nucleotide sequences to determine evolutionary relationships among organisms, to determine whether two people are related, and to identify bodies of crime victims. Chromosome

23. Organizing & packaging DNA DNA cell DNA has been “wound up” nucleus DNA in chromosomes ineveryday “working” cell cell nucleus 4 chromosomesin this organism DNA in chromosomes in cell getting ready to divide

24. DNA Packing DNAdoublehelix(2-nmdiameter Histones “Beads ona string” Nucleosome(10-nm diameter) Tight helical fiber(30-nm diameter) Supercoil(200-nm diameter) 700nm Metaphase chromosome

25. Nucleosomes 8 histone molecules • “Beads on a string” • 1st level of DNA packing • histone proteins • 8 protein molecules • positively charged amino acids • bind tightly to negatively charged DNA