Cells move around the body using cellular extensions of the plasma membrane like cilia and flagellum. They take the help of fibres outside the cell to provide anchorage. These extensions are made of microtubules, sliding against each other to produce a back and forth motion. These microtubules are a part of the cytoskeleton which will be discussed shortly. Within the cells, motor proteins attach to the receptors on organelles and use their ‘feet’ to ‘walk’ them along the fibers of cytoskeleton to their required location.
These motor proteins consume ATP (Adenosine Triphosphate) which is the source of energy at the cellular level. It is the energy currency of the cell as it provides readily releasable energy due to breaking of bonds between second and third phosphate groups.
Now that we have understood the mechanism for cell locomotion,
let’s understand more about the cytoskeleton and how its elements aid in the process.
Existence of Cytoskeleton
Cytoskeleton means skeleton of the cell. Earlier, it was
thought that cell organelles of eukaryotic cells are suspended in cytoplasm and
they float freely. (Eukaryotic cells are those which have membrane bound
organelles) But recent improvements in electron and light microscopy have led
to the discovery of cytoskeleton, a network of fibres extending throughout the
cytoplasm.
Structure and use of cytoskleton
Cytoskeleton consists of: microtubules, intermediate filaments
and microfilaments. (These are written in decreasing order of thickness). Microtubules
form the structure of cilia and flagella. The microtubules act as compression resisting
girders of the cell. Cytoskeleton provides mechanical support and is dynamic in
nature in contrast to the animal skeleton, as it can be disintegrated
in one part of the cell to be reconstructed in another part. In this way, it can
change the shape of a cell.
It also helps in cell motility (cell movement), which is our
focus in this article. Cell motility refers to both the change in cell’s location
and the movement of cell organelles within it. It provides anchorage to the motor
proteins and forms a path for organelles.
Importance of movement of organelles in human body
A vesicle is a
small sac formed by a membrane, filled with liquid. Vesicles inside cells move
substances into or out of the cell. In nerve cells, vesicles containing neurotransmitters
use motor proteins to travel along the cytoskeleton to the tips of the cellular
extensions called axons where they merge with the plasma membrane to secrete chemicals
into the synapse. This is how messages are transported through nerves in our body.
Transport of signals form the basis of nervous system.
References:
The cytoskeleton is a network of fibers that organizes
structures and activities in the cell | Chapter 6: The Cell, Campbell Biology, 12th
edition.
https://www.cancer.gov/publications/dictionaries/cancer-terms/def/vesicle