Medium · cytosol
Cytoplasm
A crowded, jostling gel
In view
Every speck is shaking with Brownian motion. Nothing is pushing them: heat alone keeps the whole soup in motion.
Everything between the membrane and the nucleus. Its fluid part, the cytosol, is about 70% water, yet it is so packed with proteins, RNA and ribosomes (up to 400 mg per millilitre) that molecules are constantly bumping into one another.
Much of the cell’s chemistry happens here: sugar is broken down, proteins are built and signals are relayed from the surface to the nucleus. Fat is stored here too, in lipid droplets wrapped in a single layer of lipid.
- Water
- ≈ 70 %
- Macromolecules
- 80–400 mg/mL
- Ribosomes
- ≈ 10 million
- pH
- ≈ 7.3
Did you know?
Despite the crowding, a typical protein can wander across a 20 µm cell in about 10 seconds, just by random jiggling.
Sources
- What are the time scales for diffusion in cells? · Milo & Phillips · Cell Biology by the Numbers
- Water as percentage of the total wet weight in HeLa cell · BioNumbers · BNID 100387
- Total intracellular concentration of proteins, nucleic acids, polysaccharides, and ribonucleoproteins · BioNumbers · BNID 114200
- 4.3 Eukaryotic Cells · OpenStax · Biology 2e
- 7.2 Glycolysis · OpenStax · Biology 2e
- 9.2 Propagation of the Signal · OpenStax · Biology 2e
- Lipid Droplets And Cellular Lipid Metabolism · Walther & Farese 2012 · Annu Rev Biochem
- Number of ribosomes in HeLa cells · BioNumbers · BNID 107347
- What is the pH of a cell? · Milo & Phillips · Cell Biology by the Numbers