Chapter 3 genetics

• A single strand of human DNA = about 1 meter long (uncoiled). The total DNA in each cell = about 2m.

  
• The nucleus of a typical cell has a diameter of 0.00034mm = 0.000013in
• A single strand of DNA contains about 3 billion base pairs.

  
• If the DNA sequence of a person was compiled in books, it would take the equivalent of 200 telephone books, each 1000 pages.
• DNA


  • Stores & transmits genetic info from one organism to next generation
  • Instructs cells on work to do

  
• Deoxyribonucleic Acid


  • Building blocks - nucleotides
  • 5-Carbon Sugar (deoxyribose)
  • Phosphate Group
  • Nitrogen Base

  
• 4 nitrogen bases


  • Adenine (A) & Guanine (G) (purines)
  • Cytosine (C) & Thymine (T) (pyrimidines)

  
• DNA Strand


  • Nucleotides bond together to form a polymer
  • Sugar & Phosphate attached by covalent bonds
  • Nitrogen bases point outward & attach to each other by hydrogen bonds (weaker)

  
• DNA Double Helix


  • Hydrogen bonds
  • Nucleotide
  • Sugar-phosphate backbone

  
• Erwin Chargaff


  • Same amount of A&T and C&G
  • A pairs only w/T - (2 H-bonds)
  • C pairs only w/G - (3 H-bonds)
  • Complementary base pairing rule
• Source of DNA


  • Streptococcus
  • Yeast
  • Herring
  • Human
• Twisted Ladder


  Sugar & Phosphate groups do not line up exactly
• Double Helix Discoveries


  • Rosalind Franklin - X-ray diffraction showed DNA helix was 2-3 strands
  • Watson & Crick - 1953 - exact structure double helix held together by nitrogen bases

  
• Anti-parallel


  The 2 strands of DNA are arranged in opposite directions (anti-parallel). The strands are identified (named) by the numbered carbon located at the end of the strand. 5' is read as 5 prime, 3' is read as 3 prime

  
• Chromosome


  • Supercoils
  • Coils
  • Nucleosome
  • Histones/proteins
  • DNA double helix

  
• If DNA were the thickness of a clothesline, the length would be 8km (5mi) long.
• In bacteria, nucleotides are replicated at a rate of about 500 per second; in mammals, about 50 per second.
• During DNA replication, only about one error occurs for every one billion nucleotides made.
• Enzymes


  • Made of Proteins
  • 100s to 1000s of chemical rxn in human body
  • Enzymes speed up rxn by millions and even billions of times
  • Single enzyme molec. acts on about 1000 substrate molecules/second
• Importance of Enzymes


  • Enzymes are biological catalysts
  • Lower the amount of energy needed for rxn
  • Not changed by rxn
  • Not used up by rxn
• Reaction pathway without enzyme


  Activation energy without enzyme
• Reaction pathway with enzyme


  Activation energy with enzyme
• Metabolism


  • Catabolism: breaking apart molecules (hydrolysis)
  • Anabolism: building molecules (dehydration synthesis/condensation rxn)
• Enzyme Naming


  • Most enzymes are named after the substrate they work on (usually ending in "-ase")
  • Lipase-lipids
  • Protease-proteins
  • Sucrase-sucrose
• DNA Replication


  1. Unzip

  2. Complementary Base Pairing

  3. Joining nucleotides

  
• DNA Helicase


  Unzips (uncoils) part of DNA strand, breaking H-bonds btwn bases

  
• DNA Polymerase


  Pairs up free nucleotides with complementary bases (forming new H-bonds)

  
• Ligase


  Joins nucleotides (S+P) with covalent bonds

  
• Semi-conservative Replication


  2 identical DNA strands, each with 1 new strand & 1 old strand

  
• DNA Polymerases

  • Also "proofreaders"
  • Only add nucleotides to growing chain, if previous base is correctly paired
  • Backtracks to correct mistake
  • Only about 1 error for every one billion nucleotides made

  
• DNA Replication Animation