Final answer:
In the context of S1-decorated microfilaments, the barbed end is called the plus end, and the pointed end is referred to as the minus end. This nomenclature reflects the polarity of F-actin, with myosin S1 fragments binding and pointing toward the minus end, signifying the direction of movement of myosin during muscle contraction.
Step-by-step explanation:
In S1-decorated microfilaments, the barbed end is known as the plus end, and the pointed end is the minus end. This relates to the inherent polarity found in F-actin (filamentous actin) filaments. When S1 fragments of myosin bind to actin filaments, they generate an arrowhead pattern which points towards the minus end. This distinctive arrowhead pattern is used to identify the direction of the filament and is consistent with the directional movement of myosin along the actin filament during muscle contraction.
The barbed end, or the plus end, is the site where actin monomers more readily associate with the filament, allowing it to grow, while the pointed end, or the minus end, is the site where disassembly is more likely to happen. Therefore, the S1-decorated microfilaments visually represent the directionality and polarity inherent in these cytoskeletal structures, which is critical to their function in cellular dynamics, including cell shape, motility, and division.
Understanding the polarity of microfilaments is essential for grasping the mechanics of muscle contraction and cellular movement, as it describes the way in which motor proteins like myosin travel along actin filaments to produce force and movement.