IB Biology C2.1 Notes

You now know about cell origin, structure, function, and differentiation. The next step is to understand how cells are able to generate responses to environmental factors or other cells via receptors. These are defined as protein with binding sites for specific signalling chemicals, called ligands. Note that receptors are specific to their particular ligand to ensure efficient and appropriate responses, preventing unnecessary energy expenditure. There are two types of receptors you are expected to be aware of:

1. Intracellular - found within the cell’s cytoplasm or nucleus. These receptors bind hydrophobic ligands able to cross the cell membrane.
2. Extracellular (transmembrane) - found spanning the cell membrane with regions both inside and outside the cell, these receptors bind hydrophilic ligands that cannot cross the cell membrane.