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 &not 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