Structure of DNA

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  • Created on: 05-02-15 15:02
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8.1 Structure of DNA
Why do living organisms vary?
How this variation is influenced by genetic and environmental factors
Nucleotide structure:
Made up of three sections:
1. A sugar called deoxyribose
2. A phosphate group
3. An organic base belonging to one of two different groups:
a) Single-ring bases
b) Double ring bases
Combined by a condensation reaction ­ gives single nucleotide (mononucleotide)
Two mononucleotides can be combined to become a dinucleotide
Continuing linking forms a long chain = polynucleotide
DNA Structure
1953 ­ Watson and Crick worked out structure of DNA, following work by Rosalind Franklin on the
X-ray diffractions of DNA: opened the door for other developments
Made up of 2 strands of nucleotides (polynucleotides)
Joined together by hydrogen bonds between certain bases
Adenineand Guaninehave double ring bases = longer molecules
Cytosineand Thyminehave single ring bases = shorter molecules
Adenine pairs with Thyminewith TWO Hydrogen Bonds
Cytosinepairs with Guaninewith THREE Hydrogen Bonds
These pairs happen because they are complementary to each other
The quantities of A+T are the same and so are the quantities of C+G but the ratio varies between

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Phosphate and deoxyribose wind round one another to create the double helix. For each turn
there are 10 base pairs.
DNA is the material responsible for passing on genetic information from cell to cell
3.…read more


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