DNA: The Genetic Material

1
DNA The Genetic Material

• Chapter 9
• Read Section Reviews

2
DNA The Genetic Code

• Griffith proved Transformation of DNA (mouse
  experiment)
• Tried to find a vaccine (weakened form to prevent
  infection
• Had 2 strains one virulent (causes disease) one
  harmless.
• Transformation foreign DNA is picked up by a
  cell.
• Avery proved DNA is the genetic code (enzyme
  extract experiment)
• Hershey Chase confirmed DNA was the genetic
  code. (blender radioactive bacteriophage
  experiment)

3
Griffiths Experiment
4
Hershey Chase Experiment

• Radioactively tag the bacteriophages.
• DNA phosphorous 32, Protein sulfur 35
• Allow Virus and cells to interact.
• Separate outside shell of virus from cell
• Find injected material

5
Structure of DNA

• DNA is a polymer of subunits called nucleotides.
• 5 carbon sugar called deoxyribose, a phosphate
  group, a nitrogenous base.
• Stores transmits the genetic information from
  one generation to the next
• Nucleotides have 2 groups Purines Pyrimidines
• Purines are Adenine Guanine and have 2 rings
• Pyrimidines are Cytosine Thymine and have 1
  ring
• The Sugars phosphates form the backbone of the
  chain and the nitrogenous bases stick out from
  the chain.

6
Double Helix Structure
7
Nitrogen Bases
8
Scientists DNA Structure

• Franklin(woman) Wilkins used X-ray images of
  DNA to show a repeating pattern and twisted
  strands.
• Chargaff found a correlation between the nitrogen
  bases
• Same of As as Ts Cs as Gs
• Watson and Crick are American and British
  scientists who first discovered the double helix
  arrangement.
• In the double helix nitrogen bases paired exactly
  opposite of each other. A (adenine) with T
  (thymine) C (cytosine) with G (guanine)
• Complementary Base pairing would look like this
  TCGAACT would bond with AGCTTGA.

9
Replication of DNA

• Before a cell divides it must replicate (copy)
  its DNA
• The enzyme DNA heliase unzips the DNA to make
  Replication Forks.
• The enzyme DNA Polymerase adds in base pairs
  complementary to the old strands creating new
  strands.
• Another DNA Polymerase enzyme proofreads the
  bases to make sure the bases match.

10
DNA Replication
11
Rate of Replication

• Several Replication Forks occur at one time to
  speed up the replication.
• Prokaryotes have circular DNA and have two
  replication forks.
• In Eukaryotes there are many forks working at one
  time.
• Human chromosomes are replicated in about 8 hours.