dna what does it look like? what does it do?. dna – a piece of the puzzle dna must be able to give...
TRANSCRIPT
DNA
What Does It Look Like?
What Does it Do?
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.
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
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
Rosalind Franklin
Rosalind Franklin used x-ray diffraction to take pictures of DNA molecules.
Her research suggested the spiral shape of DNA
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
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 pairsAdenine – ThymineGuanine - Cytosine
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
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
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.