1.3 - Membrane proteins

Fluid-mosaic model

Fluid-mosaic model

Describes the structure of the plasma membrane components including phospholipids, cholesterol, proteins, and carbohydrates

Integral proteins

Membrane proteins that interact extensively with the hydrophobic region of membrane phospholipids.​

Hydrophobic R groups

These allow strong interactions that hold integral membrane proteins within the phospholipid bilayer.

Hydrophilic R groups

Found on the surface of peripheral membrane proteins

Peripheral membrane proteins

Are bound to the surface of membranes, mainly by ionic and hydrogen bond interactions

Oxygen and Caron dioxide

Molecules that can pass through a membrane by simple diffusion

Facilitated diffusion

The passive transport of substances across the membrane through specific transmembrane proteins.​

Channel proteins

Multi-subunit proteins with the subunits arranged to form water-filled pores that extend across the membrane.​

Two types of gated channel proteins

Ligand-gated and voltage-gated

Ligand-gated channels

Controlled by the binding of signal molecules.​

Voltage-gated channel

Controlled by changes in ion concentration.​

Transporter proteins

These bind to the specific substance to be transported and undergo a conformational change to transfer the solute across the membrane.​ They alternate between two conformations so that the binding site for a solute is sequentially exposed on one side of the bilayer, then the other.​

Active transport

Uses pump proteins that transfer substances across the membrane against their concentration gradient.​

The use of ATP in active transport

Some active transport proteins hydrolyse ATP directly to provide the energy for the conformational change required to move substances across the membrane.​

ATPases

These hydrolyse ATP.

Membrane potential

This is an electrical potential difference​.​ It is created when there is a difference in electrical charge on the two sides of the membrane.

Electrochemical gradient

This is created by the combination of the concentration gradient and the electrical potential difference.​ It applies to solutes with a net charge and determines the transport of the molecule.​ Ion pumps use energy from the hydrolysis of ATP to establish and maintain ion gradients.​

Sodium-Potassium Pump

Transports ions against steep concentration gradients using energy directly from the hydrolysis of ATP.​ ​It actively transports sodium ions ​ out of cells and potassium ions ​ into cells.

The transport of Sodium and Potassium ions by the Sodium-Potassium pump

For each ATP that is hydrolysed, three sodium ions are transported out and two potassium ions are transported into cells.

Basal metabolic rate

This is the amount of energy per unit time that an animal needs to keep them functioning at rest.

Roles of the Sodium-Potassium pump

Maintaining basal metabolic rate and creating a concentration gradient in the cells of the small intestine to allow the functioning of the glucose symport.