given the set of data in the picture, propose a mechanism for how the aggregatio

Question

given the set of data in the picture, propose a mechanism for how the aggregation and dispersal of melanosomes occur.

5. Some lower vertebrates such as fish and amphibians can control their color by regulating specialized pigment cells called melanophores. These cells contain small, pigmented organelles, termed melanosomes, that can be dispersed throughout the cell, making the cell darker, or aggregated in the center of the cell to make the cell lighter. You purify the melanosomes from melanophores that have either aggregated or dispersed melanosomes and find that: 1. aggregated melanosomes co-purify with dynein; 2. dispersed melanosomes co-purify with kinesin. Given this set of data, propose a mechanism for how the aggregation and dispersal cf melanosomes occur. (3 points)

Explanation / Answer

Dynein and Kinesin are the motor proteins present in the eukaryotes. They are usually associated with microtubules during their intracellullar action like organelle transport, vesicle trafficking and cell division. The microtubules have distinct polarity for their biological activity in a cell. Tubulin polymerizes end to end i.e. the beta sub-unit of one tubulin polymerizes with the alpha sub-unit of other tubulin. Thus, the protofilament consists of an alpha sub-unit at one end which is also called as minus (-) end and the beta sub-unit at the other end called as plus (+) end. The + end is directed or located towards the plasma membrane whereas the - end is towards the center of the cell. Dynein is usually involved in the retrograde transport of the organelles that is from + end to - end. Hence, dyneins convert chemical energy from ATP into mechanical energy and help in the movement of melanosomes into the cell center thus resulting in their aggregation. In contrast to this, kinesins are usually ATPases. They utilize the energy produced by the ATP hydrolysis and helps in the melanosome transport from - end to + end which is otherwise called as anteretrograde transport. This results in the dispersion of melanosomes away from the cell center.

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