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What Does It Look Like? What Does it Do?
DNA What Does It Look Like? What Does it Do?
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DNA – A Piece of the Puzzle
DNA must be able to give instructions for building and maintaining cells DNA must be able to be copied each time a cell divides so that each cell has identical chromosomes and genes.
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Nucleotides: Building Blocks of DNA
A nucleotide is made up of a sugar, a phosphate and a base. There are four bases Adenine Thymine Guanine Cytosine
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Bases Match Up All four bases have different shapes
Guanine only matches with Cytosine Adenine only matches with Thymine Chargaff’s rule says the amount of A=T and the amount of G=C
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Rosalind Franklin Rosalind Franklin used x-ray diffraction to take pictures of DNA molecules. Her research suggested the spiral shape of DNA
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Watson and Crick’s Model
After seeing Franklin’s image, Watson and Crick determined that DNA must be shaped like a long, twisted ladder. This explained how DNA is copied and how it works in the cell
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DNA – The Double Helix The twisted ladder is called a double helix
The sides of the ladder are made of alternating sugar and phosphate molecules The rungs of the ladder are made of base pairs Adenine – Thymine Guanine - Cytosine
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Making Copies of DNA Pairs of bases allows the cell to replicate or to make copies of DNA The pairs are complementary since they always pair A-T and C-G
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How Copies are Made DNA molecules split down the middle
The bases on each side are used as a pattern for the new strand Complementary bases are added (A-T and C-G) TWO DNA molecules are formed. Half of each molecule is the old DNA, half is new DNA
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DNA and Chromosomes DNA is coiled tightly in the nucleus of cells
DNA is bundled into structures called chromosomes. DNA is copied every time a cell divides The job of unwinding, copying and rewinding the DNA is done by proteins in the cell.
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