Final answer:
Microfilaments are polar because of their directional growth, while keratin intermediate filaments lack polarity and provide structural support without directionality.
Step-by-step explanation:
Microfilaments and keratin-based intermediate filaments are both integral parts of the cytoskeleton of a cell but have distinct properties. The polarity of microfilaments is due to their directional growth, where monomeric actin proteins add on more readily to the plus end than the minus end of the filament, creating inherent polarity. This is dynamic and supports molecular motors, like myosin, in cellular processes such as muscle contraction or cell motility. Conversely, keratin intermediate filaments lack this inherent polarity; they are made of fibrous keratin proteins wound like ropes and provide tensile strength to the cell, resisting forces that pull the cell apart without directionality.
These intermediate filaments are robust, maintaining cell integrity against physical stress, and they do not show polarized growth. Keratin is essential for the cell's structural framework and does not impart polarity because it does not interact with molecular motors in a directional manner much like microfilaments do with actin and myosin. Instead, it provides the cell with tensile strength and resilience