Final answer:
The end of a growing microtubule is rich in GTP-associated tubulin molecules, which are important for microtubule dynamics and functions such as cell shape maintenance and chromosome segregation during cell division.
Step-by-step explanation:
The end of a growing microtubule is rich in GTP-associated tubulin molecules. Microtubules are dynamic cytoskeletal structures composed of α-tubulin and β-tubulin polymerized dimers. They perform many functions in the cell, including maintaining the cell's shape, facilitating intracellular transport, and segregating chromosomes during cell division. Adding to the plus end (also called the growing end) of the microtubule involves the incorporation of tubulin dimers associated with guanosine triphosphate (GTP). This GTP-tubulin adds to the microtubule and later, GTP is hydrolyzed to guanosine diphosphate (GDP), which leads to a less stable association with the microtubule, resulting in the potential for disassembly at the minus end.