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DNA DNA is a double helix.
A bonds to T: C bonds to G
In man, the DNA molecule , if fully extended, would have a total length of 1.7 metres. If you unwrap all the DNA you have in all your cells, you could reach the moon ...6000 times!
What is the structure of a gene?Genes once thought to be made of proteinChromosomes contain both DNA & protein
(histones)Cell structures are built of protein, cell
function controlled by enzymes (protein)Nucleus once thought to contain a “master
molecule” for each of cell’s protein.
Three “classic” experiments show its DNA
Griffith: Found “transforming factor” in a type of pneumonia-causing bacteria.
Avery: Found Transforming Factor was deactivated by DNA-digesting ¬ protein-digesting enzymes.
Hershey & Chase: Labeling experiments with viruses that infect bacteria.
Why the historical perspective?Classic experiments are straight-forward,
low-tech, elegant and understandable.Provide an opportunity to apply the logic
of scientific, using “what if” scenariosTo learn “How we know what we know”Knowledge builds on previous knowledge
Griffith (1928)Griffith (1928)A type of bacterial pneumonia has two forms:
“smooth” (S) causes pneumonia, but “rough” does not.
When S-type bacteria are heat-treated, they die and no longer can cause pneumonia.
But, if inject live R along with heat-killed S, the mouse gets pneumonia.
Griffith (1928)Griffith (1928)Live S bacteria found in the treated miceSo something in the heat-killed S bacteria
“transformed” the live but harmless R bacteria into pneumonia-causing S bacteria
What was this “transforming factor”
Oswald Avery (1944)Fascinated with Griffin’s workInjected protein-digesting enzymes to some
extracts-Cells were transformed Then added an enzyme that breaks apart
DNA and heredity material was blocked.Proof that it was the DNA not proteins
Side by side experiments are performed with separate bacteriophage (virus) cultures in which either the protein capsule is labeled with radioactive sulfur or the DNA core is labeled with radioactive phosphorus.
Hershey & Chase (1950)
DNADNA STRUCTUREDNA REPLICATIONDNA TRANSCRIPTIONDNA TRANSLATION
Components of DNANUCLEOTIDE
Phosphate group
5-Carbon sugarNitrogen base
(G)guanine(C)cytosine(A)adenine(T)thymine
COMPONENTS
•TAKES PLACE IN THE NUCLEUS
•END PRODUCT IS TWO IDENTICAL STRANDS
•DURING CELL DIVISION- ONE STRANDFOR EACH CELL
DNA ReplicationDNA is opened by
enzymes (unzips)Complementary
nucleotides bond with the old strands
2 strands created: ½ is the old strand; ½ is the new strand.
SUMMARY
Comparison of DNA and RNARNA is single
strandedRNA has uracil
instead of thymineA-U
DNA is double stranded
DNA has thymine instead of uracil
A-T
Understanding DNA
Inheritance/ Genetic CounselingCell function/protein synthesisEmbryonic development/gene regulationEvolution/ phylogenetic relationshipsMedicine/genetic diseasesGenetic engineering/ recombinant DNA
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