BSC-2010 Lecture Notes - Lecture 1: Streptococcal Pharyngitis, Frederick Griffith, Francis Crick

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27 Oct 2016
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Chapter 5 & 16 October 27th
DNA is the substance of inheritance
1953 James Watson and Francis Crick introduced a double-helix model
DNA is the material of genetics
- Idea is less than 100 years old
What does it mean for something to be hereditary?
- It must be passed from one generation to the next
In 1910, T.H. Morgan did an experiment with fruit flies, and showed that genes are
located on chromosomes
- Chromosomes are DNA wrapped around proteins
- The material inherited from one generation to the next
18 years later, Frederick Griffith worked with the bacteria that causes Strep throat,
Streptococcus pneumoniae. He worked with one strain that was pathogenic and one strain
that was harmless. He infected mice with the two strains.
- Pathogenic cells (s cells) which causes the mouse to die
- Non-pathogenic cells (r cells); the mouse survives
- S cells were then killed with heat; the mouse survives
- Mix heat-killed S cells with living R cells; mouse dies
- This phenomenon is called transformation
Transformation: a change in genotype and phenotype due to assimilation of foreign DNA
The application of heat irrevocably disrupts protein function but not DNA function. What
aspect of macromolecule structure do you think is most disrupted by heat?
- Hydrogen bonds
Bacteriophages Experiment (Phage Experiment)
- Uses viruses that infect bacteria
- The virus attaches itself to the surface of the cell, and then injects part of the virus
inside the cell which is capable of creating a whole new virus cell
- Radioactive sulfur labels proteins: s^35
- Radioactive phosphorus labels DNA: p^32
- Differential labeling
- Polymer
Monomers are nucleotides
5 carbon sugar, nitrogenous base, and a phosphate group
Nitrogenous Bases: A, T, G, C
- DNA composition varies from one species to the next
- Erwin Chargraff (1950):
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- A & T are always found at similar rates, and C & G are always found at similar rates
- A-C-C-G-T-A-G-C-T-A
- T-G-G-C-A-T-C-G-A-T Double stranded DNA Molecule
In any species the number of A and T bases are equal and the number of G and C bases
are equal… the percentages in the table are different because of imperfect data
Double Helix: two linear strands coiled around each other
- Rosalind Franklin’s x-ray crystallographic images of DNA
Antiparallel: subunits run in opposite directions
Two types of nucleic acids
- Deoxyribonucleic acid (DNA)
Can copy itself
- Ribonucleic acid (RNA)
A copy of a piece of DNA
m RNA is responsible for producing proteins by leaving the nucleus and
finding a ribosome
proteins are a copy of a single m RNA molecule
Nucleic acids are polymers called polynucleotides
Each polynucleotide is made of monomers called nucleotides
- Each nucleotide has a nitrogenous base, a pentose sugar, and one or more phosphate
- Nucleoside = nitrogenous base + sugar
- Two types of nitrogenous bases
Pyrimidines (cytosine, thymine, and uracil) have a single six-membered ring
Purines (adenine and guanine) have a six membered ring fused to a five-
membered ring
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