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Biology Dna Notes

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Biology notes- DNA
Structure of DNA
Nucleotide structure
Individual nucleotides of DNA are made up of three components:
A sugar called deoxyribose
A phosphate group
An organic base belonging to one of two different groups:
A single ring bases- cytosine and thymine
Double ring bases- adenine and guanine
The sugar, phosphate group and organic base are combined as a result of condensation reactions, to give a single nucleotide.
DNA structure
DNA is made up of two strands of nucleotides. Each of the two strands is extremely long, and they are joined together by hydrogen bonds formed between certain bases.
In its simplified form, DNA can be thought of as a ladder, in which the phosphate and deoxybrose molecules alternate to form the uprights and the organic bases pair together to form the rungs.
Pairing of bases
The organic bases contain nitrogen and are of two types. Those with a double ring structure- A and G, have longer molecules than those with a single ring structure C and T.
A pairs with T by 2 hydrogen bonds
G pairs with C by 3 hydrogen bonds
The quantities of adenine and thymine in DNA are always the same and so are the quantities of G and C.
However, the ratio of adenine and thymine to guanine and cytosine varies from species to species.
Double helix
The uprights of phosphate and deoxyribose wind around one another to form a double helix. They form the structural backbone of the DNA molecule. For each complete turn of this helix, there are ten base pairs.
Function of DNA
The DNA molecule is adapted to carry out its functions by:
Being very stable and can pass from generation to generation without change
Its two separate strands are only joined with hydrogen bonds, which allows them to separate during DNA replication.
By having the base pairs within the helix, the genetic information on the inside is protected by chemical and…...

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