Centrosome, Cytoskeleton and Microbodies

Introduction

What are Microbodies?

Microbodies are described as subcellular cytoplasmic organelles typically found in eukaryotic cells. They are globular in shape and consist of degradative enzymes. These degenerative enzymes are contained within a single membrane of a cell. Microbodies are found in the cytosol of a cell and are known as cytosomes. The diameter of a microbody ranges from 0.2 to 1.5 micrometres. Due to their small size, they are only visible through a microscope. A single phospholipid double-layer membrane surrounds microbodies. They also consist of a matrix of intracellular material that contains enzymes and various other proteins. The enzymes present in microbodies aid in the initial and intermediate phases of many biochemical reactions within cells. Some of the functions with which microbody enzymes help include breaking down fats, alcohol and amino acids. However, the primary functions of microbodies are the detoxification of peroxides and photorespiration in plants. Some of the most common examples of microbodies include glyoxysomes, peroxisomes, glycosomes and woronin bodies. Glyoxysomes are mainly found in the plant kingdom. They are a type of peroxisome responsible for performing the function of the glyoxylate cycle. Peroxisomes are organelles that are present in almost all types of eukaryotic cells. Their main role is to get rid of toxic peroxides and aid in the metabolic activity of fatty acids. Glycosome is described as the membrane enclosing organelle consisting of glycolytic enzymes and a dense proteinaceous matrix. It is said to have evolved from the peroxisome. Woronin bodies are peroxisome-derived dense-core microbodies with a unit membrane. They are found near the septae dividing hyphal compartments in filamentous  Ascomycota(fungi). They prevent the loss of cytoplasm post-injury and plug the septal pores post hyphal wounding.

Centrosome and Centrioles

The centrosome is a region surrounding the centrioles and is located near the nucleus. A centrosome consists of one or two centrioles surrounded by microtubules. The main function of a centrosome is the initiation and regulation of cell division. In animal cells, centrosomes are very much like DNA. During the division of cells, a single centrosome from the parent cell is transferred to every daughter cell. In proliferating cells, centrosomes start to divide before the synthesis phase or the S-phase.

The centrosome cycle consists of four phases:

1. G1 phase- Here, the duplication of centrosomes takes place.
2. G2 phase- Here, the centrosomes begin to mature.
3. Mitotic phase- Here, the separation of centrosomes takes place.
4. Late mitotic phase- This is the final phase and consists of chromosome disorientation.

Centrosomes consist of two perpendicular centrioles. These centrioles are called the daughter centriole and the mother centriole. Both the centrioles are connected together by interconnecting fibres. These fibres comprise complex proteins, which aid in the formation of additional microtubules. An amorphous pericentriolar matrix surrounds the centrioles, which are involved in the anchoring and nucleation of cytoplasmic microtubules. Centrioles are defined as a small group of microtubules arranged in a specific manner. There are nine groups of microtubules in any cell and are usually at right angles when adjacent to each other. They aid in the organisation of mitotic spindle and cytokinesis.

What are Cytoskeletons?

A cytoskeleton can be described as a network of fibres forming the prokaryotic cells, eukaryotic cells and archaeans. In eukaryotic cells, cytoskeletons consist of a complex mesh of protein filaments and motor proteins, which help in cell movement. Cytoskeletons also aid in cell division, cell signalling, transportation of molecules, organisation of organelles and providing shape and support to cells. Generally, a cytoskeleton consists of fibres like microfilaments, microtubules, intermediate filaments and proteins such as kinesin, dyneins and myosin. While microfilaments help transport materials to cells, microtubules aid in cytokinesis, gliding, and contraction. Intermediate filaments help improve cell tensile strength and the formation of keratin. Proteins such as kinesin, dyneins, and myosin help muscle contraction and move cell organelles toward the nucleus. They also help perform cytokinesis, exocytosis and endocytosis.

Conclusion

In this unit, we have looked at microbodies, their structure and types and their functions. We have also explored what centrosomes, centrioles and cytoskeletons are, along with their structure, functions and types.