Cytoplasm

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The cytoplasm is a thick, liquid residing between the cell membrane holding organelles. But it doesn't contain the nucleus.

All the contents of the cells of prokaryote organisms (which lack a cell nucleus) are contained within the cytoplasm. Within the cells of eukaryote organisms the contents of the cell nucleus are separated from the cytoplasm, and are then called the nucleoplasm.

In eukaryotic cells also, the cytoplasm contains organelles, such as mitochondria, which are filled with liquid that is kept separate from the rest of the cytoplasm by biological membranes. It is within the cytoplasm that most cellular activities occur, such as many metabolic pathways including glycolysis, and processes such as cell division. The inner, granular mass is called the endoplasm and the outer, clear and glassy layer is called the cell cortex or the ectoplasm.

The part of the cytoplasm that is not held within organelles is called the cytosol. The cytosol is a complex mixture of cytoskeleton filaments, dissolved molecules, and water that fills much of the volume of a cell. The cytosol is a gel, with a network of fibers dispersed through water. Due to this network of pores and high concentrations of dissolved macromolecules, such as proteins, an effect called macromolecular crowding occurs and the cytosol does not act as an ideal solution. This crowding effect alters how the components of the cytosol interact with each other.

Movement of the calcium ion in and out of the cytoplasm is thought to be a signalling activity for metabolic processes.[1]

Contents

Constituents

The cytoplasm has three major elements; the cytosol, organelles and inclusions.

Cytosol

The cytosol is the portion not within membrane-bound organelles. The cytosol is a translucent fluid in which the plasmic elements are suspended. Cytosol makes up about 70% of the cell volume and is composed of water, salts and organic molecules.[2] The cytoplasm also contains the protein filaments that make up the cytoskeleton, as well as soluble proteins and small structures such as ribosomes, proteasomes, and the mysterious vault complexes.[3] The inner, granular and more fluid portion of the cytoplasm is referred to as endoplasm.

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