ch 13-14

• Biologists realized they needed to do

  Understand the chemical nature of the gene
• Frederick Griffith studied


  How certain types of bacteria produce pneumonia
• Griffith's experiment


  1. Isolated 2 types of bacteria: S type and R type

  2. Injected S-type bacteria - mice died of pneumonia

  3. Injected R-type bacteria - mice were safe

  4. Killed S-type bacteria and injected them into mice, but they survived
• The cause of pneumonia was not a poison from the disease-causing bacteria
• Griffith's next experiment


  1. Mixed the dead S-type bacteria with R-type bacteria

  2. The mice died, indicating that the S-type bacteria passed on their trait to the R-type bacteria
• Transformation


  When 1 type of bacteria had been changed permanently into another
• Griffith said the transforming factor had to be a gene because the ability was inherited by the offspring
• Oswald Avery wanted to figure out

  The molecule in the heat-killed bacteria that caused the transformation
• Avery's experiment


  1. Extracted various molecules from the heat-killed bacteria and treated this mixture with enzymes that destroyed proteins, lipids, and carbs

  2. Transformation occurred, meaning that the transforming factor was neither of those things

  3. Used enzymes that broke down DNA, and transformation didn't occur
• The transforming factor is DNA
• DNA in bacteria


  Stores and transmits genetic information from one generation of bacteria to the next
• Genes


  Made of DNA
• Bacteriophage


  A virus that infects bacteria. They attach to the surface of the bacterium and inject their genetic info into it. The genes inside produce many more bacteriophages, which destroy the bacterium.
• Hershey and Chase's experiment

  1. Grew viruses in cultures containing radioactive isotopes of 32P and 35S

  2. All of the radioactivity was from 32P
• The genetic material in bacteriophage is DNA
• DNA molecule


  Capable of storing and copying information, expressing genes
• Nucleic acids


  Long, slightly acidic molecules that are built from monomers called nucleotides
• Nucleotide


  Nitrogenous base, 5-carbon sugar, phosphate group
• DNA


  Chains of nucleotides
• Nitrogenous bases of DNA

  • Adenine
  • Thymine
  • Cytosine
  • Guanine
• The nucleotides can join in any order, so any sequence of bases is possible
• Erwin Chargoff's discovery


  Amount of A=T, C=G
• Purines


  Double rings (A and G)
• Pyrimidines


  1 ring (C and T)
• Rosalind Franklin's X-ray diffraction study


  DNA has a double helix shape and nitrogenous bases are stacked near the center of the molecule
• DNA's double helix explained base pairing, how DNA strands are held together, and how DNA functioned as a carrier of genetic information
• Nitrogenous bases


  Held together by hydrogen bonds
• Base pairing explains Chargaff's rule because it gave a reason why A=T and C=G
• DNA replication


  Process of duplicating DNA
• DNA replication


  1. 2 strands of DNA separate

  2. 2 new strands are synthesized using base pairing
• Semiconservative replication


  Each resulting molecule has 1 original strand and 1 new strand
• The result of replication is 2 DNA molecules identical to each other and the original molecule
• Cells replicate their DNA so each new cell has a complete set of DNA
• Helicase


  Enzyme that unzips the strands and breaks hydrogen bonds
• DNA polymerase


  Enzyme that removes RNA primer and replaces it with DNA bases, and adds nucleotides
• Origin of replication


  Where replication starts
• Telomeres


  Tips of eukaryotic chromosomes
• Telomerase


  Enzyme that adds short, repeated DNA sequences to telomeres as chromosomes are being replicated
• Telomerase is switched off
• Replication in prokaryotes


  Single, circular strand of DNA; starts at 1 point; 2 directions