Discuss the contribution of RAS to the MAPK growth factor signalling pathway and cancer.
Huntington Disease, outlining the main symptoms and giving details of the mode of inheritance and causative mutation.
In the case of the RAS/MAPK pathway, the protein required for activation is known as a ‘mitogen’ – a small protein which has the ability to specifically trigger cell proliferation.
The mitogen will recognise and bind to a site on the outer surface of another protein (known as a ‘receptor’) which is embedded at the surface of the cell. This leads to a subtle modification in the receptor’s structure, notably the portion of the receptor which resides inside the cell. By achieving this, docking sites which can accommodate further proteins which serve to assist in the overall signalling ability of the pathway are created. This helps to build a larger ‘molecular scaffold’ of signalling molecules within the cell.
Huntington disease (HD) usually results in progressive movement, thinking (cognitive) and psychiatric symptoms. It is inherited in an autosomal dominant manner. This means that having a change ( mutation ) in only one of the 2 copies of the HTT gene is enough to cause the condition. When a person with HD has children, each child has a 50% (1 in 2) chance to inherit the mutated gene and develop the condition.