Fundamentals of Biology - Lecture Outlines: Chapter 13: DNA Structure and Function
DNA =
- structure confirmed by Watson and Crick (1953)
How did scientists determine the structure and function of DNA?
Griffith:
Looking for vaccine for pneumonia
Rough bacteria = non-virulent
Smooth bacteria = virulent (causes pneumonia)
Inject mice with:
1. Live rough (R) cells
2. Live smooth (S) cells
3. S cells killed by heating them
4. Live R cells and heat-killed S cells
Something in the S cells transformed the R cells
Avery:
used extracts from bacteria
- concluded that DNA
Hershey and Chase:
- bacteriophages
- viruses that infect bacteria
Proteins have sulfur
DNA has phosphorus
EXPERIMENT:
Label virus coat with radioactive sulfur
- Labeled virus allowed to infect bacteria
- Label (viral coat) stays on outside of cell
CONCLUSION: proteins are not
Label virus with radioactive phosphorus
- Allow labeled virus to infect bacteria
- Labeled DNA inside bacteria
CONCLUSION: DNA is genetic material
DNA Structure
Nucleotide:
5 carbon sugar + phosphate group + nitrogen-containing base
4 bases:
adenine, guanine
thymine, cytosine
Chargaff's Rules:
1. Amount of adenine relative to guanine differs from one species to the next
2. amount of adenine = amount of thymine
Humans have about 30% adenine.
How much T, G, and C?
How are bases arranged?
X-ray diffraction
Rosiland Franklin concluded that DNA was:
- long
- uniform diameter
- highly repetitive
- helical
Watson and Crick :
- Single-ringed thymine bonded to double-ringed adenine
- "Backbone" = sugars and phosphates
- double strands
Base-pairing is constant for all species
Sequence of base pairs differs
DNA Replication
- duplication of DNA strands
- only works in one direction
- must add nucleotides to the exposed -OH group
1. Two DNA strands unwind
2. Unattached nucleotides pair
3. Short stretches of DNA joined together
Semiconservative replication
Review:
Review questions 1-3
Self quiz 1-7
Critical thinking # 1,2