Negative charge is a term referring to the formation of an atom. There must be negatively charged sub-particles to stabilise the structure of an atom. This is due to the widely accepted modern Rutherford-Bohr model of an atom. The formation of an atom is formulated by electrons along a shell that repel amongst themselves therefore in their orbitals, electrons preferably like to fill the empty orbitals first. Electrons are pulled towards the nucleus due to its attraction to the protons within the nucleus. Please note that protons are positively charged, and the nucleus are composed of neutrons (no charge) and protons.
A negative charged ion is usually formed by a loss of an electron or from accepting electrons during ionic bonding. For instance:
Cl2(aq) + 2Na(s) → 2Na+ + 2Cl- → 2NaCl(aq)
Chlorine becomes a chloride ion and sodium becomes a Sodium ion through ionic bonding (the electrostatic attraction between negative and positive ions). Chlorine accepts two electrons from Sodium to maintain the octet shell to obtain the Lewis structure of [2,8,8] from [2,8,7] as Chlorine is a molecule (formed by divalent bonding between two Chlorine atoms). On the other hand, Sodium donates two electrons (one electron from each sodium atom) to Chlorine (each atom) to maintain the octet rule to for form [2,8].
The significance of negative charged molecules in biological science is that they have an influence of the movement of ions and molecules across the plasma membrane. A good example of negative charged ions/molecules (or even charged molecules/ions) is in Cell Biology, there is a chemical disequilibrium in cell tissue – intracellular fluid and the extracellular fluid, influenced by potassium ions, sodium ions, calcium ions and chloride ions. The chemical disequilibrium comes from the constant movement of sodium ions and potassium ions move across the extracellular fluid to the intracellular fluid, while calcium and chloride ions move across the endothelium capillary.