Nucleic acids
Nucleic acidsDNA is the single most important molecule found within cells. It is a stable polynucleotide, which contains coded information for inherited characteristics. It is contained in chromosomes in the nucleus of an eukaryot cell. The essential features of the Watson-Crick model are summarised below.
1. The two helical polynucleotide chains are coiled around a common axis. The two chains have opposite polarity i.e. they are antiparrallel.
2. The regular repeating sugar phosphate backbone of each strand lies on the outside of the helix. The purine and pyrimidine bases project inwards at 900 to the axis of the helix.
3. The two strands are held together by hydrogen bonding between pairs of bases such that guanine always pairs with cytosine and adenine always pairs with thymine; this is called complementary base pairing
3. The diameter of the helix is 2.0 nm and adjacent bases are separated by 0.34 nm and inclined at 360 relative to each other. This means that each complete turn of the double helix contains about 10 base pairs.
4. The amount of guanine is usually equal to that of cytosine.
The monomers of RNA and DNA are called nucleotides. Each nucleotide has three parts:
A Five Carbon or Pentose Sugar
The sugar will be one of two very similar pentose rings. Ribonucleic acids contain the sugar...
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