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DNA & RNA

DNA & RNA. Section 1 DNA. Discovery of DNA. Griffith’s Experiment - 1928. Heat-killed, disease-causing bacteria. Harmless bacteria. Harmless bacteria. Disease-causing bacteria. Heat-killed, disease-causing bacteria. Control (no growth). Lives. Dies of pneumonia. Lives.

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DNA & RNA

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  1. DNA & RNA

  2. Section 1 DNA

  3. Discovery of DNA

  4. Griffith’s Experiment - 1928 Heat-killed, disease-causing bacteria Harmless bacteria Harmless bacteria Disease-causing bacteria Heat-killed, disease-causing bacteria Control(no growth) Lives Dies of pneumonia Lives Dies of pneumonia Live, disease-causingbacteria The harmless bacteria had been permanently changed or “transformed” into the disease-causing bacteria

  5. GriffithExperiment

  6. Transformation • Fred Griffith worked with 2 differnet strains of bacteria: virulent S (causes pneumonia) and nonvirulent R (does not cause pneumonia) strain Pneumoccocus bacteria • He found that R-strain could become virulent when it took in DNA from heat-killed S-strain • Concluded that the transforming factor might be a gene.

  7. Oswald Avery – repeated Griffith’s experiment (1944) • He concluded: DNA stores and transmits the genetic information from one generation to the next

  8. Hershey-Chase Experiment - 1952 Alfred Hershey & Martha Chase experimented using Bacteriophages (a virus that infects and kills bacteria) • Composed of a DNA or RNA core and a protein coat • Attaches to a cell and injects its genetic information Proved that DNA was the cell’s genetic material Radioactive 32P was injected into bacteria!

  9. Percentage of Bases in Four Organisms Source of DNA A T G C Streptococcus 29.8 31.6 20.5 18.0 Yeast 31.3 32.9 18.7 17.1 Herring 27.8 27.5 22.2 22.6 Human 30.9 29.4 19.9 19.8 What do you notice about the amount of A compared to T and the amount of G compared to C?

  10. Discovery of DNA Structure • Erwin Chargaffshowed the amounts of the four bases on DNA ( A,T,C,G) • % of A were roughly equal to the % of T and the % of G were roughly equal to the % of C

  11. C T A G Chargaff’s Rule • Adeninemust pair with Thymine • Guanine must pair with Cytosine • The bases form weak hydrogen bonds

  12. DNA Structure • Rosalind Franklin (1952) took diffraction x-ray photographs of DNA crystals • Showed an X-shaped pattern with twisted strands

  13. DNA Structure Watson and Crick – built cardboard models using Franklin’s x-rays; Given credit for determining the structure of DNA

  14. DNA Structure

  15. DNA • Stands for Deoxyribonucleic acid • Made up of subunits called nucleotides • Nucleotide made of: 1. Phosphate group 2. 5-carbon sugar 3. Nitrogenous base

  16. Phosphate Group O=P-O O 5 CH2 O N Nitrogenous base (A, G, C, or T) C1 C4 Sugar (deoxyribose) C3 C2 DNA Nucleotide O

  17. DNA • Two strands coiled called a double helix • Sides made of a 5-carbon sugar Deoxyribose bonded to phosphate (PO4) groups (the backbone) • Center made of nitrogen bases bonded together by weak hydrogen bonds

  18. “Rungs of ladder” Nitrogenous Base (A,T,G or C) “Legs of ladder” Phosphate & Sugar Backbone DNA Double Helix

  19. A or G T or C Nitrogenous Bases • Double ring PURINES Adenine (A) Guanine (G) • Single ring PYRIMIDINES Thymine (T) Cytosine (C)

  20. 3 H-bonds G C Base-Pairings • Purines only pairwith Pyrimidines • Three hydrogen bonds required to bond G & C

  21. A T Two hydrogen bonds required to bond A & T

  22. 5 O 3 3 O P P 5 5 C O G 1 3 2 4 4 2 1 3 5 O P P T A 3 5 O O 5 P P 3 DNA

  23. DNA Section 12-1 Nucleotide Hydrogen bonds Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Sugar-phosphate backbone A to T with double bond G to C with triple bond A & G Purines (2 rings) C & T Pyrimidines (3 rings)

  24. DNA structure

  25. Microscopic Image of DNA

  26. Section 2: Chromosomes and DNA Replication

  27. Where is DNA found in the cell? • Prokaryotes – DNA is in the cytoplasm (because they do not have a nucleus!) • One circular strand of DNA • One chromosome that contains all the genetic information

  28. Eukaryotes – DNA is in the nucleus as a number of chromosomes • The number of chromosomes varies by species • Humans have 46 chromosomes • Fruit flies have 8chromosomes • Dogs have 78chromosomes

  29. DNA Length: • DNA is long • It must be folded dramatically to fit in cells (it’s like trying to fit a thick rope that is 1000 feet long into a small backpack!)

  30. Chromosome Structure • Eukaryotic chromosomes contain both DNA and protein tightly packed together to form chromatin • Chromatin consists of DNA that is tightly coiled around proteinscalled histones • DNA and histone molecules form a beadlike structure called a nucleosome

  31. Chromosome Structure of Eukaryotes Nucleosome Chromosome DNA double helix Coils Supercoils Histones

  32. DNA Replication • The copying of DNA • Each strand of DNA can re-build the other half due to base pairing (A-T and G-C) • Strands are complementary • Replication begins at many places on the DNA segment and continues in BOTH directions • Replication Forks – sites where separation and replication occur

  33.  DNA Replication New strand Original strand DNA polymerase Growth DNA polymerase Growth Replication fork Replication fork Nitrogenous bases Original strand New strand

  34. 3’ Parental DNA Molecule 5’ Replication Fork 3’ 5’ DNA Replication • Begins atOrigins of Replication • Two strands separateformingReplication Forks (Y-shaped region) • 2 New strands grow at the forks

  35. How Replication Occurs • Replication is carried out by a series of enzymes • Main replication enzyme is DNA polymerase • Enzymes “unzip” DNA by breaking the hydrogenbondsbetween bases • DNA polymerase joins individual nucleotides to produce a new DNA molecule • DNA polymerase also “proofreads” each new DNA strand

  36. What would be the complementary strand of DNA for the following: A T C T T G C G G A A T G G T A G A A C G C C T T A C C

  37. Example of Replication: If the original DNA molecule contained the following base pairs: A C G T A A T G C T G C A T T A C G The two strands would separate into: A C G T A A T G C and T G C A T T A C G The complementary bases would then pair with each of these strands to form two new strands of DNA

  38. Replication of Strands Replication Fork Point of Origin

  39. Section 3:RNA and Protein Synthesis

  40. Genes - coded DNA instructions that control the production of proteins • To decode the instructions and make protein, DNA is copied into RNA

  41. The Structure of RNA • Long chain of nucleotides like DNA • 3 main differences between DNA and RNA • RNA’s sugar is ribose • RNA is single stranded • In RNA, Uracil (U), replaces Thymine (T) • Main job of RNA is protein synthesis (assembly of amino acids into proteins)

  42. Example of an RNA strand that is made from DNA If this is your strand of DNA: A T G T A C G T A What would be the complementary strand of RNA? U A C A U G C A U Remember Uracil (U) replaces Thymine (T) in RNA!!

  43. There are 3 main types of RNA 1. mRNA – messenger RNA • Carry copies of instructions for assembling amino acids into proteins • “messengers” from DNA to the rest of the cell 2. rRNA – ribosomal RNA • Combine with protein to form ribosomes 3. tRNA – transfer RNA • Transfers each amino acid to the ribosome as it is specified by coded messages in mRNA (pictures)

  44. Transcription • Step 1 of protein synthesis • Making mRNA from DNA • Process in which part of the nucleotide sequence of DNA is copied into a complementary sequence of RNA

  45. Transcription requires the enzyme RNA polymerase • This enzyme: • Binds to DNA • Separates theDNA strands • Uses one strand of DNA as a template to assemble a strand of RNA

  46. How does RNA polymerase know where to start and stop making RNA from DNA? • Enzyme will only bind to regions of DNA known as promoters, which have specific base sequences • Tells the enzyme where to start and stop!

  47. RNA editing • RNA requires editing before it goes into action • Introns – DNA sequences that are NOT used to make proteins • Exons – DNA sequences that DO code for proteins • Both introns and exons are copied, but the introns are removed before mRNA leaves the nucleus

  48. The Genetic Code • Proteins are made by joining amino acids into long chains called polypeptides • There are 20 different amino acids • The characteristics of proteins are determined by the order in which the amino acids are joined

  49. The genetic code is the “language” of mRNA instructions • Remember RNA has 4 bases: adenine, uracil, cytosine, guanine • The genetic code is read three letters (bases) at a time • Each three-letter word is known as a codon, which stands for an amino acid

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