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Discoveries in DNA: From Transformation to Protein Synthesis

This chapter explores early discoveries in DNA, including the transformation experiments by Fred Griffith and Oswald Avery, as well as the Hershey-Chase experiments with bacteriophages. It also covers the identification of DNA as the genetic material and the discovery of DNA's double helix structure by Rosalind Franklin, Maurice Wilkins, Francis Crick, and James Watson. The chapter further discusses the process of DNA replication and protein synthesis, including transcription and translation.

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Discoveries in DNA: From Transformation to Protein Synthesis

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  1. Chapter 9 DNA – The Genetic Material

  2. EARLY DISCOVERIES… • Fred Griffith – trying to develop a vaccine for pneumonia …..TRANSFORMATION

  3. Oswald Avery…. • Discovered that the substance absorbed by the harmless bacteria was DNA… • DNA is the Transformation factor!

  4. Hershey – Chase Experimentstudies bacteriophages…

  5. Discovering DNA: • Erwin Chargaff found • that the amount of Adenine always equals the amount of Thymine !....AND that Guanine amounts always equaled Cytosine. • Rosaline Franklin and Maurice Wilkins –X-Ray diffraction shows DNA is a coiled helix

  6. Francis Crick and James Watson • Discovered the 3-dimensional structure of DNA……. Showing base pairing in a double helical staircase…..Nobel prize 1950

  7. Structure of DNA • I. DNA: (Deoxyribonucleic Acid) • Building blocks called… • Nucleotides: (3 parts): • 1.Deoxyribose (simple sugar) • 2.Phosphate Group • 3.Nitrogen Base(A, C, T or G) • ADENINE • CYTOSINE • THYMINE • GUANINE

  8. BASE PAIRING PURINES – ADENINE AND GUANINE PYRIMIDINES - THYMINE AND CYTOSINE ADENINE – HYDROGEN BOND – THYMINE GUANINE – HYDROGEN BOND - CYTOSINE

  9. THE SIDES OF THE DNA MOLECULE PHOSPHATE DEOXYRIBOSE SUGAR PHOSPHATE DEOXYRIBOSE SUGAR PHOSPHATE

  10. DNA = 2 strands of nucleotides joined by hydrogen bonds between the bases forms a “DOUBLE HELIX” or twisted ladder

  11. A. DNA Replication: • Each organism has its unique nucleotide sequence in its DNA --->from parents • DNA must be copied • for cell division • (Replication)

  12. STEPS IN DNA REPLICATION: • Enzymes called DNA Helicases break bonds between bases - DNA “unzips”

  13. Free nucleotides in pair up with exposed bases guided by DNA Polymerases. • 2 new strands formed and rewind • (identical to original DNA) Free nucleotides

  14. …….How proteins • are made !!

  15. II. PROTEIN SYNTHESIS: 20 Different amino acids 3 Nitrogen bases code for 1 amino acid = CODON “Triplet code” - 64 different codons (3 stop codons) ---> 20 amino acids Order of bases in DNA determines type and order of amino acids in protein Code is universal among all organisms = common ancestor

  16. A. TRANSCRIPTION: Getting DNA to make a m RNA ….which carries the sequence for a particular polypeptide chain! • DNA IS IN THE NUCLEUS • Transcription takes place in the nucleus! • RNA structure differs from DNA: • Single strand of nucleotides • Ribose - simple sugar • Bases - uracil instead of thymine U -- A A, U, C, G

  17. STEPS OF TRANSCRIPTION: 1. DNA makes complimentary copy of mRNA (using U in place of T) 2. mRNA carries code out of nucleus into cytoplasm where ribosomes are located!

  18. B. TRANSLATION: Interpreting the code from the mRNA - on the ribosomes. • tRNA (transfer) carries amino acids and bring them to ribosomes to be assembled into proteins • The order of amino acids determines the type of polypeptide assembled. (protein)

  19. tRNA has anticodon (3 bases that code for a specific amino acid) • tRNA matches its anticodon with the mRNA codon and drops off its amino acid to bond with the next amino acid • Continues until a “stop codon” is reached

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