Dictionary:

cytoplasm

  (sī'tə-plăz'əm)

The protoplasm outside the nucleus of a cell.

That portion of living cells bordered externally by the plasma membrane (cell membrane) and internally by the nuclear envelope. In the terminology of classical cytology, the substance in living cells and in living organisms not compartmentalized into cells was called protoplasm. It was assumed at the time that the protoplasm of various cells was similar in structure and chemistry. Results of research on cell chemistry and ultrastructure after about 1960 showed that each cell type had a recognizably different “protoplasm.” Primarily for that reason, the term protoplasm gradually fell into disuse in contemporary biology. The terms cytoplasm and nucleoplasm have been retained and are used descriptively; they are used almost synonymously with the terms cytosome (body of cytoplasm) and nucleus, respectively.

Many cells, especially the single-celled organisms or protistans, have regional cytoplasmic differentiation. The outer region is the cortex or ectoplasm, and the inner region is the endoplasm. In many cases the cortical layer is a gel made up of a meshwork of cytoskeletal fibers.

Cytoplasm contains mostly water, from 80 to 97% in different cells, except for spores and other inactive forms of living material, in which water may be present in lesser amounts. The dry mass of cells consists mainly of macromolecules: proteins, carbohydrates, nucleic acids, and lipids associated with membranes. The small molecules present in cells are mainly metabolites or metabolic intermediates. The principal ions other than the hydrogen and hydroxyl ions of water are the cations of potassium, sodium, magnesium, and calcium, and the anions chloride and bicarbonate. Many other elements are present in cytoplasm in smaller amounts. Iron is found in cytochrome pigments in mitochondria; magnesium is present in chlorophyll in chloroplasts; copper, zinc, iodine, bromine, and several other elements are present in trace quantities. See also Cytochemistry.

Sedimentation of cells by centrifugation shows that organelles and inclusions can be separated from the ground cytoplasm, the fluid phase of the cytoplasm in which they are suspended. The ground cytoplasm in turn has been shown to consist of a cytoskeletal network and the cytosol, the fluid in which the cytoskeleton is bathed. The cytoskeleton consists of several biopolymers of wide distribution in cells. Microtubules have been observed in electron micrographs of a vast number of different cell types. They consist of the protein tubulin, and are frequently covered by a fuzzy layer of microtubule-associated proteins. See also Cytoskeleton.

In most cells the smaller particles exhibit Brownian motion due to thermal agitation. In some cells lacking extensive cytoskeletal structure, particles can be moved freely around the cell by Brownian motion. In others they are restricted by their surrounding cytoskeletal elements. Particles of various types may also undergo saltatory motions which carry them farther than Brownian motion possibly could. Such excursions result from the interaction of a particle with an element of the cytoskeleton such as one or more microtubules or microfilaments. See also Cell (biology).

For more information on cytoplasm, visit Britannica.com.

That part of a cell inside the cell surface membrane, but outside the nucleus. It consists of a watery fluid, the cytosol, in which cell organelles are suspended.

The material within a biological cell that is not contained in the nucleus or other organelles.

The protoplasm of a cell surrounding the nucleus (nucleoplasm).

Organelles. Cytoplasm labeled at center right.

Schematic showing the cytoplasm, with its components (or organelles), of a typical animal cell. Organelles: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (6) Golgi apparatus (7) cytoskeleton (8) smooth endoplasmic reticulum (9) mitochondria (10) vacuole (11) cytosol (12) lysosome (13) centriole.

Cytoplasm is a gelatinous, semi-transparent fluid that fills most cells. Eukaryotic cells contain a nucleus that is kept separate from the cytoplasm by a double membrane layer. The cytoplasm has three major elements; the cytosol, organelles and inclusions. The cytosol is the gooey, semi-transparent fluid in which the other cytoplasmic elements are suspended. Cytosol makes up about 70% of the cell and is composed of water, salts, organic molecules, and enzymes that are necessary for the cell to catalyze reactions.^[1] The organelles are the metabolic machinery of the cell and are like little organs themselves. The major organelles that are suspended in the cytosol consists of the mitochondria, proteins, ribosomes, the endoplasmic reticulum, the Golgi apparatus, lysosomes, and the cytoskeleton. The inclusions are chemical substances that store nutrients, secretory products and pigment granules. ^[2]

Function

The cytoplasm is the site where most cellular activities are done. All the functions for cell expansion, growth and replication are carried out in the cytoplasm of the cell. The cytosol has enzymes that take molecules and break them down , so that the individual organelles can use them as they need to. The cytosol also contains the cytoskeleton which gives the cell its shape and can help in the movement of the cell. ^[3]

References

1. ^ Cytoplasm Composition
2. ^ Cytoplasm - Filling Fluid - from Biology4Kids.com
3. ^ Cytoplasm

External links

• Human Anatomy & Physiology, seventh edition By; Elain N Marieb and Latja Hoehn.
• What is cytoplasm? - by Genevieve Thiers -2002
• Glencoe Science Biology The Dynamics of Life

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