DNA & Protein Synthesis

History

  • Franklin:: crystallized DNA and took pictures of it
  • Wilkins:: Franklin’s colleague; shared the pictures with Watson & Crick without her permission
  • Watson & Crick:: compared other scientists’ work on DNA, saw Franklin’s photographs, discovered double helix structure
  • Avery-MacLeod-McCarty Experiments:: continued Griffith’s experiments on transformation; removed aspects of virulent bacteria (proteins, RNA, or DNA) and exposed them to non-virulent strains; observed that without DNA, the non-virulent strains didn’t transform
    • bacteria transformation:: gene transfer by which some bacteria take up foreign genetic material from the environment
  • Hershey-Chase Experiment:: tagged proteins of viruses with radioactive sulfur and DNA with radioactive phosphorus to see which entered the cell; observed that bacteriophages infected their DNA into cells to make more copies

DNA and RNA

  • closely related organisms have similar genetic code with more similar DNA or RNA nucleotide sequences than distantly related organisms
  • DNA:: double stranded, made of chromosomes, deoxyribose sugar (5 carbon atoms), T A G C nitrogenous bases, stores genetic information
  • RNA:: single stranded, ribose sugar, U A G C nitrogenous bases, stores information for protein synthesis, read by ribosomes
    • mRNA:: carries genetic info of DNA from nucleus to cytoplasm for protein synthesis
    • rRNA:: makes up ribosome with other proteins
    • tRNA:: carries amino acids to mRNA to form polypeptide
  • Central Dogma:: termed by Crick; theory stating that genetic info flows from DNA→ RNA → protein, or RNA directly to protein

DNA Replication

  • DNA Replication Steps
    • 1) helicase unwinds parental double helix
    • 2) molecules of single strand binding protein stabilize unwound template strands
    • 3) leading strand is synthesized continuously in the 5’→ 3’ direction by DNA polymerase III
    • 4) primase begins synthesis of RNA primers for the Okazaki fragments
    • 5) DNA pol III adds DNA nucleotides to 3’ end of RNA primers
    • 6) DNA pol I removes RNA primer from 5’ end of Okazaki fragments, replaces with DNA nucleotides
    • 7) DNA ligase bonds 3’ end of one fragment to 5’ end of another fragment; glues Okazaki fragments together
  • Semiconservative Replication:: when two copies of the original DNA molecule are produced, each copy contains one original strand and one newly-synthesized strand

RNA Synthesis

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