Question

Why must most material (such as proteins, lipids, carbohydrates, and new organelles) be produced in the cell body? In other words, why can’t these materials be built right in the synaptic knobs if that is where they are needed?

Explain fast axonal transport, covering the following: How fast is it? What structure in a neuron’s axon is used as a pathway or “train track” for materials to be moved to and from the neuron cell body (soma)? What proteins can travel on this track, and which direction can each go?

What is the name of the part of the kinesin protein that looks like feet? What powers each “step” of the kinesin molecules along the microtubule and how does the “step” then happen?

Answer 1

Most materials are produced in the cell body(soma) because the precursor molecules for the synthesis enter soma by selective transporters on the cell membrane. More over the machinery and enzymes required for the synthesis is present in the cell body.

For example : enzyme choline acetyl transferase is present in the cell body which is used for the synthesis of acetylcholine from choline and acetate.

Fast axonal transport is the cellular process responsible for the movement of mitochondria, lipids, synaptic vesicles, Proteins and other organelles from the cell body.

It is transported at a rate of ~200 - 400mm/day.

Microtubules runs along the length of the axon and provide the main cytoskeletal track for the transport of substance.

KINESIN & DYNEIN are motor protein that move substance from the cell body to axon tip(anterograde) and from tip to cell body (reterograde).

Mitochondria, cytoskeletal polymers, autophagosomes, synaptic vesicles are some of the substance transported.

Anterograde movement facilitated by kinesin. It carries microtubules amd neuro filaments at a rate ~0.1-1 mm/day. Actin molecules at 2-3 mm/day. HSV reactivation i.e virus migrate from dorsal root ganglion of neurons to skin by anterograde movement.

Reterograde movement facilitated by dynein. Through this send chemical messages and endocytosis products heades to endolysosomes from the axon back to the cell body. Some pathogens also invade through this route( rabies, tetanus toxin).

Feet like part of the kinesin protein is called head of the kinesin ( heavy chain). Kinesin moves along microtubules powered by hydrolysis of ATP( adenosine triphosphate). Hydrolysis of ATP results in the dissociation of kinesin from microtubules and it explains the movement of kinesin on microtubules.