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					Deoxyribose Nucleic Acid

DNA

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 protein • Chromosomes 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.

Identifying the Genetic Material
Three “classic” experiments show its DNA
Griffith: Found “transforming factor” in a type of pneumonia-causing bacteria. Avery: Found TF was deactivated by DNAdigesting &not protein-digesting enzymes. Hershey & Chase: Labeling experiments with viruses that infect bacteria.

Why the historical perspective?
• Classic experiments are straightforward, low-tech, elegant and understandable. • Provide an opportunity to apply the logic of scientific, using “what if” scenarios • To learn “How we know what we know” • Knowledge builds on previous knowledge

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)
• Live S bacteria found in the treated mice • So 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 work • Injected 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

Hershey & Chase (1950)

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.

DNA

•DNA •DNA •DNA •DNA

STRUCTURE REPLICATION TRANSCRIPTION TRANSLATION

Components of DNA
• NUCLEOTIDE
– Phosphate group – 5-Carbon sugar – nucleic acid (1 of the nucleic acids)
• • • • guanine cytosine adenine thymine

COMPONENTS

DNA REPLICATION
•TAKES PLACE IN THE NUCLEUS
•END PRODUCT IS TWO IDENTICAL STRANDS

•DURING CELL DIVISION- ONE STRAND FOR EACH CELL

DNA Replication
• DNA 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.

DNA TRANSCRIPTION
DNA- GIVES CODE TO mRNA

tRNA translates mRNA into proteins

DNA TRANSLATION

SUMMARY

Comparison of DNA and RNA
• RNA is single stranded • RNA has uracil instead of thymine • A-U • DNA is double stranded • DNA has thymine instead of uracil • A-T

Understanding DNA
• Inheritance/ Genetic Counseling • Cell function/protein synthesis • Embryonic development/gene regulation • Evolution/ phylogenetic relationships • Medicine/genetic diseases • Genetic engineering/ recombinant DNA


				
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posted:6/27/2008
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