Corpus: Cytoplasm

The cytoplasm is the entire living content of a cell, which is enclosed on the outside by the cell membrane. In plant cells, which have a huge central vacuole inside them, the cytoplasm is delimited on the outside by the plasmalemma and on the inside - against the vacuole - by the tonoplast, another biomembrane.

The cytoplasm itself consists of:

• the cell fluid (cytosol or hyaloplasm)
• the cytoskeleton (cytoskeleton)
• the cell organelles (note: only in eukaryotes)

In prokaryotes (e.g. bacteria) the genetic material in the form of DNA lies freely in the cytoplasm, in eukaryotes it lies in the cell nucleus.

A topographical distinction is made between different compartments of the cytoplasm:

• Endoplasm: central, inner compartment of the cytoplasm
• Ectoplasm: outer layer of the cytoplasm
• Axoplasm: cytoplasm within the axon of a nerve cell

In chemical terms, the cytoplasm consists of numerous organic and inorganic substances. With 80 to 85% water content, the water content is high. The following list shows the average composition of animal cells:

• Water 80.5-85 %
• Proteins 10-15 %
• Lipids 2-4 %
• Polysaccharides 0.1-1.5 %
• DNA 0.4 %
• RNA 0.7 %
• small organic molecules 0.4 %
• Inorganic molecules and ions 1.5 %

The pH value of the cytoplasm is usually around 7. However, as protons are often bound or released during metabolic reactions, the cytoplasm is buffered. The pH value can also be changed or stabilised by ion pumps.

The cytoplasm contains the cytoskeleton, which is dynamically built up and broken down. This stabilises the cell, provides fixed pathways for vesicle transport and causes intracellular movements such as cytoplasmic streaming, organelle and chromosome transport. Cytoplasmic streaming only takes place in the endoplasm and contributes to mixing.

See also: Nucleoplasm, proteasome