Schematic of typical animal cell, showing subcellular components.
Organelles:
1 Nucleolus
2 Nucleus
3 Ribosomes (little dots)
4 Vesicle
5 Rough endoplasmic reticulum
6 Golgi apparatus
7 Cytoskeleton
8 Smooth endoplasmic reticulum
9 Mitochondria
10 Vacuole
11 Cytosol
12 Lysosome
13 Centrioles within Centrosome
14 Cell membrane

The cytoplasm comprises cytosol — the gel-like substance enclosed within the cell membrane — and the organelles — the cell's internal sub-structures. All of the contents of the cells of prokaryote organisms (such as bacteria, 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. The cytoplasm is about 70% to 90% water and usually colorless.

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.

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

In plants, movements of the cytoplasm around vacuoles are known as cytoplasmic streaming.

Constituents[edit]

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

Cytosol[edit]

The cytosol is the portion of the cytoplasm not contained within membrane-bound organelles. Cytosol makes up about 70% of the cell volume and is composed of water, salts and organic molecules.^[2]

The cytosol is a complex mixture of cytoskeleton filaments, dissolved molecules, and water that fills much of the volume of a cell. The cytosol 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.

Proteins in different cellular compartments and structures tagged with green fluorescent protein

Due to this network of fibres 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.

Organelles[edit]

Organelles (literally "little organs"), are usually membrane-bound, and are structures inside the cell that have specific functions. Some major organelles that are suspended in the cytosol are the mitochondria, the endoplasmic reticulum, the Golgi apparatus, vacuoles, lysosomes, and in plant cells chloroplasts.

Cytoplasmic inclusions[edit]

The inclusions are small particles of insoluble substances suspended in the cytosol. A huge range of inclusions exist in different cell types, and range from crystals of calcium oxalate or silicon dioxide in plants,^[4][5] to granules of energy-storage materials such as starch,^[6] glycogen,^[7] or polyhydroxybutyrate.^[8] A particularly widespread example are lipid droplets, which are spherical droplets composed of lipids and proteins that are used in both prokaryotes and eukaryotes as a way of storing lipids such as fatty acids and sterols.^[9] Lipid droplets make up much of the volume of adipocytes, which are specialized lipid-storage cells, but they are also found in a range of other cell types.

Controversy and research[edit]

The cytoplasm, mitochondria and most organelles are contributions to the cell from the maternal gamete. There is considerably less research and understanding on cytoplasmic inheritance/maternal inheritance and mitochondrial DNA compared to the cell nucleus and genomic DNA. Historically, there has been neglect of researching whatever has been labeled female or feminine. The cytoplasm is one organelle that has been labeled feminine.^[10] The cytoplasm/nucleus being labeled as feminine/masculine follows the example of egg/sperm being gendered; both cytoplasm and egg are considered nonresistant to the efforts and pursuits of the active nucleus and sperm. The "passivity of the egg becomes the passivity of the cytoplasm."^[11] Contrary to the older information that disregards any notion of the cytoplasm being active, new research has shown it to be in control of movement and flow of nutrients in and out of the cell by "viscoplastic behavior and... a measure of the reciprocal rate of bond breakadge within the cytoplasmic network."^[12]

Notes[edit]

External links[edit]

• Luby-Phelps K (2000). "Cytoarchitecture and physical properties of cytoplasm: volume, viscosity, diffusion, intracellular surface area" (PDF). Int Rev Cytol 192: 189–221.