Structure and Functions of Cytoplasm

Cytoplasm is the thick, gel-like semitransparent fluid that is found in both plant and animal cell. It is bounded by the plasma membrane, and contains many organelles in an eukaryotic cell (cell containing membrane bounded nucleus). In the eukaryotic cell, the nucleus is separated from the cytoplasm by a double membrane, known as nuclear membrane. Cytoplasm was discovered in 1835. Though, discovery of the different organelles found in cytoplasm can be attributed to different scientists, no single scientist can be credited for discovering cytoplasm.

Structure of Cytoplasm
Basically, cytoplasm is the fluid, where the organelles remain suspended. So, it fills up the cell, especially the spaces not occupied by any organelle. The constituent parts of cytoplasm are cytosol, organelles and cytoplasmic inclusions.

Cytosol
Cytosol is the part of the cytoplasm that is not occupied by any organelle. It is a gelatinous substance. It mainly consists of cytoskeleton filaments, organic molecules, salt and water. Cytoskeleton filaments are made up of protein filaments, and they are responsible for giving the shape to the cell. It also contains enzymes, fatty acid, sugar and amino acid. Besides, ribosomes, proteasomes and soluble proteins can also be found in cytoplasm. Cytosol accounts for almost 70% of the total cell volume.

Organelles
Cytoplasm also contains some important organelles like mitochondria, endoplasmic reticulum, lysosomes and Golgi apparatus. Besides, it also contains chloroplast in plant cells. Each organelle is bounded by a fatty membrane, and has some specific functions.

Cytoplasmic Inclusions
Some insoluble suspended substances found in cytosol are known as cytoplasmic substances. They are basically granules of starch and glycogen, and they can store energy. Besides, crystals of some minerals and lipid droplets can also be found in cytoplasm. Lipid droplets are composed of lipids and proteins, and they act as a storage of fatty acid and steroids.

Functions of Cytoplasm
Cytoplasm is the site of many vital biochemical reactions crucial for maintaining life. It is the place where cell expansion and growth take place. It provides a medium in which the organelles can remain suspended. Besides, cytoskeleton found in cytoplasm gives the shape to the cell, and facilitates its movement. It also assists the movement of different elements found within the cell.

The enzymes found in the cytoplasm breaks down the macromolecules into small parts so that it can be easily used by the other organelles like mitochondria. For example, mitochondria cannot use glucose present in the cell, unless it is broken down by the enzymes into pyruvate. They act as catalysts in glycolysis, as well as in the synthesis of fatty acid, sugar and amino acid. Cell reproduction, protein synthesis, anaerobic glycolysis, cytokinesis are some other vital functions that are carried out in cytoplasm.

Organelles present in cytoplasm have some specific vital functions; for example, the function of mitochondria is to produce and store energy, while endoplasmic reticulum facilitates synthesis and transport of protein, production of steroids, production as well as storage of glycogen, etc. The important functions of Golgi apparatus include modification, packaging, transportation and processing of macromolecules, like proteins, and lipids. On the other hand, lysosomes contain digestive enzymes and hence, they digest food particles, damaged or worn-out organelles and also virus and bacteria. However, the smooth operation of all these functions depend on the existence of cytoplasm, as it provides the medium for carrying out these vital processes.