Composition of cells

The average, non-specialised body cell can be broken down into certain common biochemical constituent molecules:

• DNA: the genetic cell template
• water:
  • the largest component: occupies more than two thirds of cell
  • provides a fluid environment for chemical reaction
  • gives cell volume and support
  • a substrate for vital metabolic reactions
• electrolytes; much different to the concentrations in the extracellular fluid:
  • potassium is key intracellular ion
  • sodium at relatively low concentration
  • minute concentrations of magnesium, bicarbonate, phosphate, chloride and sulphate
  • calcium concentration is normally relatively low in relation to extracellular fluid: this permits its use as an intracellular signalling molecule; signals transducted across the cell membrane cause a rapid rise in calcium levels
    • calcium also acts as a co-factor for a number of specialised proteins
  • trace ions e.g. manganese, zinc, iron, copper and selenium all combine with proteins, usually enzymes, to act as co-factors

proteins:

þþ structural proteins e.g. cytoskeletal tubulin

• enzymes:
  • present in cytoplasm and membrane
  • vital role in all cell metabolism, the transduction of signals to and from their environment, and special functions dependent on the cell, e.g. striated muscle contractility through actin and myosin
• carbohydrate: many roles including alteration of proteins and glycogen energy source
• lipids: acts as vital membrane constituent and energy store