Membrane Protein : Integral/Peripheral

• Integral Membrane Proteins (transmembrane)– Exposed to aqueous

environment on both sides of the membrane

– Used to transport molecules across membrane

• Peripheral Membrane Proteins – Located on surface of a

membrane – Eg. Cytoskeleton

Passive Membrane Transport • No chemical energy required• Diffusion– Net movement of a substance from a region of high

concentration to a region of low concentration until dynamic equilibrium between cells is met

Simple Diffusion (Passive Transport)

• Diffusion of small/non-polar molecules across plasma membrane unassisted

Facilitated Diffusion • Diffusion of large/polar molecules with the help of a

transport protein (integral membrane protein)• Stops when equilibrium is reached• Two types of Transport (Integtral) Proteins – Channel proteins– Carrier proteins

Facilitated Diffusion • Channel Proteins– Form hydrophilic pathways in the membrane – Water and certain ions can pass

Facilitated Diffusion • Carrier Proteins – Form pathways through the membrane– Bind to a specific solute (glucose, amino acid)– Carrier protein changes shape allowing solute to move

from one side of the membrane to the other

Osmosis • Passive diffusion of water across a

membrane via aquaporins • Water always diffuses from an area of

low solute concentration (high water concentration) to an area of greater solute concentration (low water concentration)

• Three Solutions (Cell) • Hypotonic

– Solute concentration is high in cell (swells)• Hypertonic

– Solute concentration is low in cell (shrinks)• Isotonic

– Solute and water concentration is equal both in and outside cell

Active Membrane Transport• Substance carried

across a membrane from an area of low concentration to an area of high concentration

• Use of pump• ATP used as energy

source

Exocytosis and Endocytosis • Vesicles are used to

transport• ATP is required• Exocytosis– Transport of proteins and

waste material from cytosol to exterior of cell

• Endocytosis– Transport proteins and

large molecules into cytosol of the cell.