Quiz 1

• DNA: Deoxyribonucleic Acid is the molecule that transmits traits from parent to offspring.
• Nitrogen Bases in DNA: Adenine, Guanine, Cytosine, Thymine
• DNA: A long molecule made up of two strands of nucleotides bound together in the shape of a double helix. (Twisted Ladder)

  
  

  Found in the nucleus of cells.

  
  

  Each rung of the ladder is composed of repeating units called Nucleotides.
• Nucleotide: Subunit of the DNA molecule made up of the following:

  Phosphate Molecule

  5 carbon sugars (Deoxiribose in DNA, Ribose in RNA)

  Nitrogen Base
• Nitrogen Bases:

  These are molecules containing nitrogen.

  They form the "rungs" in the DNA double helix.

  The bases are complementary. Adenine bonds with Thymine. Guanine bonds with Cytosine.
• The nitrogen bases are found in one of the two categories:

  Purines: Nitrogen bases with a double ring structure. These are Adenine and Guanine.

  Pyrimidines: Nitrogen bases with a single structure. These are Thymine and Cytosine.
• In the DNA molecule 1 Pyrimidine bonds with 1 Purine (Hydrogen bonds keep them together)
• DNA is said to be 'antiparallel'. This means that the phosphate bridges of the molecule run in opposite directions in each strand.
• The 5' end of one strand is opposite the end 3' end of the other strand and vice versa.
• Miescher isolated a substance known as "Nuclein" from white blood cells. He said that nuclein was composed of an Acid portion (he called it nucleic acid) and an alkaline portion (later shown to be a protein).

  Research after Miescher showed that nuclein was made up of a series of strand-like complexes of nucleic acids and proteins tightly bound together.

  These strands were called Chromosomes.
• Levene isolated two types of Nucleic acids distinguished by type of sugar in them. (DNA and RNA)

  Levene showed that nucleic acids are made up of long chains of individual units called nucleotides.

  
  

  He said DNA and RNA contained equal amounts of nucleotides. This was an error.
• A nucleotide is a structure composed of a five carbon sugar, a phosphate group and a Nitrogen base.
• Griffith studied bacteria and pneumonia. He found that dead pathogenic bacteria passed on their pathogenic properties to live non-pathogenic bacteria. He called this the Transforming Principle.
• Avery, MacLeod and McCarty did an experiment to try prove Griffith's transforming principle by isolating what was causing it.

  They proved that DNA was the material responsible for the transforming principle.
• Chargaff overturned Levenes's conclusion about nucleotides.

  Chargaff found that the four nucleotides were not present in equal amounts, but in varying proportions.
• Chargaff's Rule: In any sample of DNA the amount of Adenine=Thymine and Guanine=Cytosine
• Hershey and Chase gave the final proof that DNA and not Proteins carried genetic information.
• Wilkins and Franklin did work on determining the structure of nucleic acids and DNA. They took X-rays of DNA that proved it had a "helical" shape. They found that DNA had two distinct and repeating patterns.
• Wilkins and Franklin found that Nitrogenous bases were "hydrophobic" and contained within the center of the helical structure.

  They also found that the sugar-phosphate backbone was "hydrophilic" and was located on the outside.
• Watson and Crick worked on different models of the "helical" structure. They produced the structural model of DNA that is still in use today. They called their model the "Double Helix".