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DNA (Structure of DNA (One molecule of DNA consists of two polynucleotide…
DNA
Structure of DNA
Polymer made up of repeating monomeric units called nucleotides
One molecule of DNA consists of two polynucleotide strands.
The strands run in opposite directions
Strands are anti-parallel
DNA molecules are long
Carry a lot of encoded genetic information
Purines
Two rings
Adenine
Binds to thymine
Two hydrogen bonds
Guanine
Binds to cytosine
Three hydrogen bonds
This gives equal sized 'rungs' on the DNA
These can twist into a double helix
This gives the molecule stability
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Pyrimidines
One ring
Thymine
Binds to adenine
Two hydrogen bonds
Cytosine
Binds to guanine
Three hydrogen bonds
Nucleotides
They form the monomers of nucleic acids
DNA
Pentose sugar is deoxyribose
RNA
Pentose sugar is ribose
They help many metabolic pathways, such as ATP, ADP and AMP
Phosphate esters of pentose sugars
Nitrogenous base is linked to the C1 of the sugar residue
Phosphate group is linked to either
C5
C3
of the sugar residue by covalent bonds (phosphodiester bonds) formed by condensation reactions
May be components of many co-enzymes
Anti-parallel sugar-phosphate backbones
Ladder part of the DNA molecule
Formed by sugar-phosphate backbones of the antiparallel nucleotide strands
Opposite directions
Refer to the direction of where the third and fifth carbon molecules on deoxyribose are facing
5' end of molecule
Where the phosphate group is attached to the fifth carbon atom
3' end of molecule
Where the phosphate group is attached to the third carbon atom
Rungs of the ladder
It consists of complementary base pairs
Joined by hydrogen bonds
Molecule is very stable
Organisation in cells
Eukaryotic cells
Majority of the DNA (genome) is in the nucleus
Each DNA molecule is tightly wound around histone proteins into chromosomes
One molecule of DNA is one chromosome
Loop of DNA without histone proteins that are inside mitochondria and chlorplasts
Prokaryotic cells
DNA is in a loop within the cytoplasm
Not enclosed within a nucleus
DNA is not wound around histone proteins
Therefore, DNA is described as naked
Viruses with DNA also have it formed in a loop of naked DNA