Final answer:
The dynamic instability model describes the behavior of microtubules, which rapidly grow and shrink via the GTP cap's influence on the addition of tubulin subunits. The GTP cap stabilizes the growing microtubule, and its loss leads to microtubule depolymerization, affecting cell functions like mitosis and motility.
Step-by-step explanation:
Dynamic Instability Model and the GTP Cap
The dynamic instability model is a concept used to describe the behavior of microtubules within cellular structures. Microtubules are dynamic polymers made up of tubulin subunits that rapidly grow and shrink, which is crucial for their functions in cell division, intracellular transport, and maintenance of cell shape. The instability arises from the microtubule's ability to switch between phases of growth and shrinkage—known as 'catastrophe' (transition from growth to shrinkage) and 'rescue' (transition from shrinkage to growth).
The GTP cap plays a significant role in this model. As tubulin subunits add to the growing end of a microtubule, they are bound to guanosine triphosphate (GTP). This GTP-bound form promotes further addition of subunits, enabling the microtubule to elongate. However, GTP is hydrolyzed to guanosine diphosphate (GDP) over time. A microtubule with a 'cap' of GTP-bound subunits at its end is stabilized and can continue to grow; once the cap is lost and GDP-bound subunits are exposed, the microtubule quickly undergoes depolymerization, or 'catastrophe.'
The dynamic behavior of microtubules influenced by the GTP cap is central to many cell functions, including mitosis and motility. Any disruption in this dynamic equilibrium can have profound implications on cell stability and function, as observed in various cellular processes and pathologies such as cancer, where GTPase activity of proteins like RAS may be affected.