Detailed notes on nucleotides.


  • DNA
  • RNA
  • Base pairing
  • ATP and ADP
  • Phosphorylation.
  • DNA Replication
  • Genetic Code
  • Protein Synthesis

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A nucleotide is a type of biological molecule that is composed of a pentose sugar, a
phosphate group and a nitrogenous base.
They contain the elements Carbon, Hydrogen, Oxygen, Nitrogen and Phosphorus.
Nucleotides are monomers that make up DNA and RNA.
The sugar component is Deoxyribose.
The base of each nucleotide varies as there are four possibilities; adenine, thymine,
guanine or cytosine.
A molecule of DNA contains two polynucleotides.
DNA is confined to the nucleus.
DNA is needed for cell division.
The sugar component is ribose.
The possible bases are thymine, adenine, cytosine and uracil.
RNA consists of a single polynucleotide.
RNA is not confined to the nucleus.
RNA is used in transcription.
Base Pairing:

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A purine base contains two carbon nitrogen rings.
Adenine and guanine are purines.
A pyrimidine contains one carbon nitrogen ring.
Thymine, cytosine and uracil are pyrimidine.
Adenine pairs with Thymine in DNA.
Adenine pairs with uracil in RNA.
Cytosine pairs with guanine in DNA and RNA.
Between adenine and thymine there are two hydrogen bonds.
Between cytosine and guanine there are three hydrogen bonds.
Phosphorylated Nucleotides
Phosphorylated nucleotides are nucleotides that contain more than one phosphate
group.…read more

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ATP is synthesised from ADP and inorganic phosphate using the energy from an
exergonic reaction (energy releasing reaction.)
The ADP is phosphorylated to form ATP.
Energy is stored in a phosphodiester bond.
When this energy is needed by a cell ATP is broken back down into ADP and
inorganic phosphate. Energy is released from the phosphodiester bond.
This happens via a hydrolysis reaction.
DNA Replication
The DNA molecule uncoils and unzips. The hydrogen bonds between the
complementary bases break.…read more

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It is the order of nitrogenous bases that determine the order of amino acids in a
Different sequences of bases code for different amino acids.
DNA is degenerate because there are more possible combinations of triplets than
there are amino acids. There are 64 possible triplets but there are only 20 different
amino acids. This means that some amino acids can be coded for by more than one
triplet.…read more


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