Membrane Permeability

Overview of Membrane Permeability

Membrane permeability refers to the ability of a membrane to allow substances through.
Biological membranes are selectively permeable, meaning they allow specific substances through while keeping others out.
This selectivity is crucial for maintaining the integrity of the cell and its internal conditions.

Size of Molecules: Smaller molecules can pass through the membrane more easily than larger ones.
Polarity of Molecules: Non-polar, fat-soluble molecules pass through easily while charged, water-soluble molecules have difficulty.
Concentration Gradient: Substances often move across membranes from areas of high concentration to areas of lower concentration in a process called passive transport.

Passive Transport: This process requires no energy (ATP). Molecules can pass directly through the membrane if they are small and non-polar (simple diffusion), or via protein channels if they are larger or polar (facilitated diffusion).
Active Transport: This process requires energy to move substances against their concentration gradient, and involves protein carriers.
Osmosis: This is a specific type of passive transport involving water molecules. Water moves across a selectively permeable membrane from areas of low solute concentration to areas of high solute concentration.

Transport proteins, including carrier and channel proteins, play a vital role in facilitating membrane transport.
Carrier proteins bind to a specific molecule and change shape to carry the molecule across the membrane.
Channel proteins form pores in the membrane, allowing certain molecules or ions to pass through.

Increased temperature results in an increased rate of diffusion. This is because molecules move faster and bombard the membrane more often.
However, if the temperature gets too high, the cell membrane could be damaged, leading to a condition called thermal lysis, that increases membrane permeability dramatically.