S-Cool Revision Summary

S-Cool Revision Summary

Many observations contributed to the evidence from which the structure of DNA was eventually deduced by Watson and Crick:

  1. Chemical Analysis
  2. Chargaff's work on base equivalence
  3. Franklin and Wilkins' work on X-ray crystallography

Ribonucleic acid (RNA) is also a polynucleotide. The chain of nucleotides is formed in exactly the same way as in DNA, but the molecule has some very important differences:

  1. It is a single stranded molecule.
  2. The pyrimidine Thymine never occurs but is always replaced by Uracil, another pyrimidine. (Think "No cup of T for U!")
  3. It is much smaller than DNA.
  4. It comes in three different forms, ribosomal, transfer and messenger.

DNA is a polymer of nucleotides.

Nucleotides are made up of:

a phosphate.

a sugar - deoxyribose.

a base - either adenine, guanine, thymine or cytosine.

DNA is a macromolecule polymer made of subunits called nucleotides. The nucleotides are arranged in two chains which are coiled into a spiral shape called a double helix.

Since DNA forms the genetic code and that it is known that genes may be inherited, it follows that DNA must be copied exactly before being incorporated into gametes at meiosis.

It also follows that all new cells in an organism must gain a copy of the genes at mitosis, because they are able to continue the characteristic biochemical behaviour of that organism.

DNA is the molecule which controls the synthesis of proteins. Proteins are used for growth and repair and also as enzymes, in which form they catalyse all other cellular activities.

Thus DNA is able to exert a controlling influence over the whole cell and ultimately, the whole organism. The segments of DNA which hold the key to this control are the genes.

Protein synthesis relies on the effective communication of the coded information held in the genes to the sites of protein manufacture, the ribosomes in the cytoplasm.

Since DNA is part of larger structures (chromosomes), which are unable to move from the nucleus, intermediate messenger molecules are needed. These are messenger RNA molecules.