Passing information between cells

Plasma membrane function

Defines the boundary of the cell and controls passage of materials and information across it.

Mechanisms for crossing the plasma membrane

Diffusion of lipophilic molecules, ion channels, transporters, and vesicular transport (endocytosis/exocytosis).

Specialized cell communication

Different cell types require intercellular signalling to coordinate their functions.

Lipophilic messenger property

Must be made on demand because they diffuse freely across membranes and cannot be stored.

Transporters exporting messengers

Used by some cells (especially bacteria) to move chemical signals across the plasma membrane.

Vesicular release of messengers

Used by eukaryotic cells to store and release neurotransmitters and hormones.

Ion channel signalling

Opening of channels allows rapid ion movement down gradients to change membrane potential.

Allosteric membrane receptors

Convey information by undergoing conformational change when a ligand binds extracellularly.

Voltage-gated ion channels

Open in response to membrane potential and mediate fast electrical signalling.

Ca²⁺ as intracellular messenger

Entry via voltage-gated Ca²⁺ channels converts electrical signals into biochemical responses.

Neurotransmitter-gated ion channels

Ligand binding opens channels to depolarize (cation-permeable) or hyperpolarize (Cl⁻-permeable) cells.

Purpose of intracellular membranes

Create compartments with specialized environments and functions.

Protein origin

All proteins (except mitochondrial-encoded ones) begin synthesis on cytosolic ribosomes.

Mitochondrial genome

Encodes a small number of proteins; mitochondrial diseases are maternally inherited.

Protein targeting principle

Proteins remain in the cytosol unless they contain address labels that target them to specific organelles.