Question

a Which motor protein is likely to be moving the organelles along the microfilaments and which direction along the microfilaments will these move?

b After streaming stopped when cells were prodded in tap water why do you think the streaming resumed after ~1 minute?

c When cells are prodded, Ca²⁺ enters the cell by which process(es): simple diffusion, facilitated diffusion, active transport, secondary active transport, symport and/or antiport?

Answer 1

Ans a) Motor proteins are proteins which move along the animal cell cytoplasm and they use ATP hydrolysis to convert the chemical energy into mechanical energy. The motor protein that helps in the movement of the organelle along the microfilaments are myosin. Myosin moves along the microfilament with help of the actin monomers. This protein helps in the muscle contraction by ATP hydrolysis. As it moves along the microfilament, it allows the organelle and cytoplasm to move in one particular direction. They help in the cytoplasmic streaming. The myosin II is the most abundant motor protein that drives the ATP hydrolysis. The movement along the microfilament is towards the plus end of the microfilament.

Ans b) The streaming of cells when prodded in tap water stops due to the application of the pressure and hence it stops moving in a particular direction. The streaming means when there is movement of the fluid substance within the cell and it helps in nutrient transportation. However, it was observed that due to the application of pressure, the streaming stops and as soon as the cell is withdrawn from the tap water, it rearranges itself and starts the streaming process.

Ans c) The Ca2+ generally enters through secondary active transport system where movement of one ions is facilitated by another ion. It is mostly the antiport movement which helps in movement or entering of Ca2+ into the cells. An example can be the sodium/calcium exchange where movement of calcium inside the cell in facilitated by movement of sodium outside.