Structure of DNA

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Homework Define (Page ) RNA Messenger RNA Ribosomal RNA Transfer RNA Transcription RNA polymerase PromoterIntronExon

Review Homework List the conclusions that Griffith and Avery drew from their experiments? Griffith concluded that heritable substance transforms harmless bacteria into harmful bacteria. Avery found this is DNA

Review Homework What was the experimental variable that Avery used when he repeated Griffith’s work? Molecule-destroying enzyme he used

Review Homework What conclusions did Hershey and Chase draw from their experiments? DNA is the genetic material found in genes

Components of DNA What does DNA stand for? Deoxyribonucleic acid Made up of nucleotides joined into long strands and chains Made up of 5 carbon sugar called deoxyribose and phosphate Has 4 nitrogen bases: adenine, guanine, cytosine and thymine Commonly referred to as A, G, C, T

Components of DNA Nitrogen bases are bases that contain nitrogen These bases stick out sideways from each other Can be joined in any order

Structure of DNA Erwin Chargaff Showed percentages of adenine and thymine are almost always identical in DNA Percentages of Guanine and Cytosine are also almost identical What conclusion would you draw from this? A=TG=C

Structure of DNA Rosalind Franklin Took x-ray diffraction pictures that revealed the double-helix structure of DNA Only showed a 2-D model of DNA, but presents in X- shape James Watson and Francis Crick Built a model of the DNA molecule that explained both structures and properties of DNA Used Franklin’s x-shape to discover Double-Helix

The Double Helix The double helix explains Chargaff’s rule of base pairing Model shows: 2 strands in double helix run in opposite directions with bases in the center Each strand carries a sequence of nucleotides, arranged like letters of alphabet for recording genetic info Hydrogen holds strands together Chemically speaking, H bonds strong or weak? H bonds form only between pairs (AT – CG) Base Pairing

The Double Helix Like a twisted ladder or a spiral staircase Each strand is “antiparallel” Antiparallel? Run in opposite directions

Base Pairing The perfect fit of Adenine with Thymine Guanine and Cytocine Why are the weak Hydrogen bonds important? Think of the functions of DNA

Final Questions Why did scientists have to resort to methods other than a microscope? Explain the idea of base pairing?

Homework Define (Page ) RNA Messenger RNA Ribosomal RNA Transfer RNA Transcription RNA polymerase PromoterIntronExon