Introduction to Membrane Transport
- Membrane transport is how solutes are transported across a lipid bilayer
- Plasma membrane surrounds the cell which communicates with its exterior release
environment
o Retains nutrients and prevents influx of toxic substances
- Activity is determined by proteins that sit in that membrane and dictates influx and efflux
Relative permeability of a lipid membrane
Transmembrane transport
- Necessary for a cell to possess a lipid bilayer
- Enables it to define its own intracellular medium that it compatible with the biochemical
reactions essential for replication and metabolism
- Passage of ions and solutes must be facilitated by proteins which catalyse selective transport
of nutrients into/out of the cell
Essential additional roles:
- Bioenergetics: e.g. the transport of ions involved in ATP synthesis.
o The principle source of ATP in most cells are reactions at the ‘energy-coupling’
membranes of the mitochondria, chloroplasts and bacteria
- Signal Transduction: rapid translocation of ions across a membrane can have 2 profound
effects on how cells perceive signals + communicate.
o 1) electrical signalling via actions potentials
o 2) Ca2+ based signalling
- Compartmentalisation: eukaryotic cells comprise of more than one membrane – delimited
intracellular compartment.
o Evolution of these compartments has enabled metabolic flexibility e.g. formation of
storage organelles, lytic organelles or those which enable cells to develop relatively
large volumes at small metabolic cost
Overview of transport at biological membranes
- The Nernst potential is the transmembrane voltage (or electrical potential) at which
transmembrane ion movement is at equilibrium for a given ion concentration gradient
o The Nernst equation calculates the Nernst potential
- Membrane transport is how solutes are transported across a lipid bilayer
- Plasma membrane surrounds the cell which communicates with its exterior release
environment
o Retains nutrients and prevents influx of toxic substances
- Activity is determined by proteins that sit in that membrane and dictates influx and efflux
Relative permeability of a lipid membrane
Transmembrane transport
- Necessary for a cell to possess a lipid bilayer
- Enables it to define its own intracellular medium that it compatible with the biochemical
reactions essential for replication and metabolism
- Passage of ions and solutes must be facilitated by proteins which catalyse selective transport
of nutrients into/out of the cell
Essential additional roles:
- Bioenergetics: e.g. the transport of ions involved in ATP synthesis.
o The principle source of ATP in most cells are reactions at the ‘energy-coupling’
membranes of the mitochondria, chloroplasts and bacteria
- Signal Transduction: rapid translocation of ions across a membrane can have 2 profound
effects on how cells perceive signals + communicate.
o 1) electrical signalling via actions potentials
o 2) Ca2+ based signalling
- Compartmentalisation: eukaryotic cells comprise of more than one membrane – delimited
intracellular compartment.
o Evolution of these compartments has enabled metabolic flexibility e.g. formation of
storage organelles, lytic organelles or those which enable cells to develop relatively
large volumes at small metabolic cost
Overview of transport at biological membranes
- The Nernst potential is the transmembrane voltage (or electrical potential) at which
transmembrane ion movement is at equilibrium for a given ion concentration gradient
o The Nernst equation calculates the Nernst potential
