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Unraveling DNA: Structure, Function, and Genetic Material Discovery

Explore the intricate structure and essential functions of DNA, the building blocks of life. Learn about nucleotides, nitrogenous bases, DNA packaging, gene expression, and how DNA was identified as the genetic material through historic experiments. Delve into the double helix structure, nucleotide roles, and gene expression variations in this captivating journey through the molecular world of DNA.

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Unraveling DNA: Structure, Function, and Genetic Material Discovery

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  1. DNA Structure and Function(Not on mid2)

  2. Nucleic Acids (polymer) Monomer = nucleotides, the building blocks of nucleic acids Structure = three parts: sugar, phosphate, and nitrogen-containing base

  3. Sugar-Phosphate Backbone Nucleotides connected together with a covalent bond. Alternating sugars and phosphates

  4. Nucleic Acids • RNA: Four bases: • Adenine (A) • Guanine (G) • Uracil (U, replaces T) • Cytosine (C) • Sugar is ribose • Single stranded • DNA: Four bases: • Adenine (A) • Guanine (G) • Thymine (T) • Cytosine (C) • Sugar is deoxyribose • Double stranded

  5. Nitrogenous Bases • DNA -Four bases: • Adenine (A) ad-den ēn • Guanine (G) • Thymine (T) • Cytosine (C) • Memory trick, • pyrimidines have a “y” in the name

  6. Base Pairing • DNA is 2 strands (molecules) held together by H-bonds • Bases form hydrogen bonds with each other • A pairs with T (& vc vs) • C pairs with G (& vc vs)

  7. DNA Where are the H-bonds?

  8. DNA Structure The bonds between which 2 bases are stronger G&C or A&T? H-bonds are very week, break & reform W/ thousands of bases & thousands of bonds, DNA is held together

  9. DNA DNA is a polar molecule It also has a negative charge Dissolves well in water

  10. Determining that DNA is the Genetic Material • Everyone knows …DNA…genetic material • This was not always known • Early studies .. microscopes.. genetic material was in the chromosomes • Made of both protein & DNA • Most biologist .. 1940 .. protein as .. more complex. • Review experiments … DNA .. the genetic material

  11. Griffith’s Experiment • 1928 • Two strains of bacteria • R – harmless (1) • S – deadly (2) • Heat killed Strain S is also harmless (3) • Something from heat killed Strain S makes Strain R deadly (4)

  12. Avery, MacLeod, and McCarty • 1944 • Isolated compounds from Strain S • Added these to Strain R • DNA transformed Strain R into Strain S • “Proved” DNA was the genetic material

  13. Determining that DNA is the Genetic Material HERSHEY – CHASE: 1952 Determined that the heredity material was DNA & not protein Studied the bacteria virus T2 Head DNA Tail Tail fiber 300,000

  14. Determining that DNA is the Genetic Material Radioactive protein Empty protein shell Radioactivity in liquid Phage Bacterium Phage DNA DNA Batch 1 Radioactive protein Centrifuge Pellet Mix radioactively labeled phages with bacteria. The phages infect the bacterial cells. Centrifuge the mixture so bacteria form a pellet at the bottom of the test tube. Measure the radioactivity in the pellet and the liquid. Agitate in a blender to separate phages outside the bacteria from the cells and their contents. Radioactive DNA Batch 2 Radioactive DNA Centrifuge Radioactivity in pellet Pellet

  15. Determining that DNA is the Genetic Material • DNA in pellet, protein in the supernatant • The pellet contained the viral genetic material not the liquid supernatant • “Proving” DNA is the genetic material

  16. The Structure of DNA FRANKLIN and WILKINS: 1950’s X-ray crystalography determined that DNA is a double helix

  17. The Structure of DNA WATSON and CRICK: 1953 Determined that DNA was a double helix Made a DNA model

  18. Determining the Structure of DNA Watson & Crick later won the nobel prize Rosalind Franklin died of cancer young Brief video of photo 51 For more info see: http://www.pbs.org/wgbh/nova/photo51/

  19. DNA Structure in more detail Two strands run in opposite directions

  20. Nucleotide Functions Nucleotides Play Diverse Roles in Organisms: Used as “energy currency” in cells (ATP) Are chemical messengers of cells, (cAMP) Nucleotide coenzymes transport electrons and hydrogen atoms (examples: NADH and FADH2) Nucleotides also serve as building blocks for nucleic acids

  21. Nucleic Acid Functions DNA stores genetic information (traits and inheritance) RNA translates this genetic info into protein

  22. Organization of DNA • Eukaryotes • Billions of base pairs – several linear chromosomes • Genes not grouped • Mostly non-coding DNA • Nucleus? 22

  23. DNA in the cell Humans have 3 billion nucleotide base pairs Roughly 6 feet of DNA in the nucleus of each cell How does it all fit?

  24. DNA Packaging • Eukaryotic chromosomes are very large • Must be packaged • Unavailable for transcription • Unpacking must occur before transcription

  25. Levels of DNAPackaging • Fully condensed, seen at metaphase • Tightly packed loops • 30 nm fibers • Histone spool • Double helix

  26. Gene Expression Every cell in your body came from 1 original egg and sperm Every cell has the same DNA and the same genes Except the gametes which have half the DNA/genes 26

  27. Gene Expression • Every cell has the same DNA, yet, each cell is different, specialized • How can they differ? • Due to gene expression • Which genes are turned on/off • How much product they make 27

  28. Gene Expression DNA must be copied faithfully when cells divide so that DNA is the same in all cells Will have a lesson on gene expression

  29. Chromosome Animation Review of of DNA Packaging http://www.biostudio.com/demo_freeman_dna_coiling.htm (Works in Internet Explorer, may not in FireFox)

  30. Organization of DNA • Prokaryotes • Several million base pairs - one circular piece • Related genes grouped together • Mostly coding DNA • Nucleus? 30

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