AS Biology Structure of DNA

As revision notes on STRUCTURE OF DNA. aqa.

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DNA

DNA = DeoxyriboNucleic Acid.

Double helix structure.

DNA is a chemical that determines inherited characteristics and it contains genetic code.

Made up of 3 basic components to form a nucleotide. DNA is a POLYnucleotide due to being made up of many nucleotides.

Basic Components = Dioxyribose (pentose sugar), Phosphate Goup and an organic base (A,T,G,C).

Phosphate group \ \ Deoxyribose --------- Organic Base

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DNA

There are 4 possible organic bases - A = adenine

T= Thymine

G = Guanine

C = Cytosine

Each base can only join to its complimentary bases. A joins to T and G joins to C.

the organic base is the only part of DNA that changes. The phosphate and sugar group stay the same.

Organic bases are of two types; double and single ringed.

Double ringed = A and G, Guanine produces 3 hydrogen bonds

Single ringed = C and T, Thymine produces 2 hydrogen bonds.

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DNA

Two poly nucleotides join together to form a double helix.

In one strand, deoxyribose joins with the phosphate group to create a sugar-phosphate backbone.

The 2 poly nucleotide strands join together by hydrogen bonds that from between the 2 complimentary bases.

The phosphate group, deoxyribose sugar and organic base are all joined together in a process called condensation.

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In every DNA molecule the phosphate group, deoxyribose sugar and 4 bases are the same. It is the ratio quantity of these bases that differs and more importantly, the sequence in which they are in in the double helix.

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DNA

DNA storage in EUKARYOTIC CELLS>

- Contain linear DNA that exists as CHROMOSOMES.

- DNA molecule is really long and winds up into the nucleus.

- The DNA is wound around proteins; Histone proteins.

- DNA is then wound up very tightly and compact to make a chromosome.

- The DNA is associated with proteins.

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DNA storage in PROKARYOTIC-

- Also as chromosomes but DNA MOLECULES ARE SHORTER AND CIRCULAR.

The DNA isn't wound round histone proteins.

The DNA condenses to become more compact by a process called SUPERCOILING.

The DNA isn't associated with proteins like in eukaryotic cells

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Comments

Katie

this is good :) thanks

Florence

Soo helpful

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