1. Metabolism & Survival
Key Area 1b
Membrane Proteins

2. Learning Intentions
Describe the role of membranes in relation to the formation of components with cells
Describe the functions of proteins embedded in the plasma membrane

3. Metabolism and Membranes

4. Membranes and metabolic pathways
The membrane system allows transport both within cells (mitochondria, chloroplasts) and between cells.
Membranes form surfaces and compartments for metabolic pathways to allow high concentrations of required enzymes/substrates and reaction rates

5. The plasma membrane
The membrane is made up of a bilayer of phospholipids with proteins embedded in it.
This is described as the fluid mosaic model.
Fluid – lipid bilayer can move, proteins can move laterally
Mosaic – the proteins can be arranged in any order like a mosaic

6. Phospholipid Structures
Phospholipids are made of hydrophobic tails and hydrophilic heads. The tails pack closely together to avoid the tissue fluid (or blood) and the heads form a barrier.
The smallest structure they form is a micelle (single layer) but if another layer is added it will form a centre with heads also to the inside which can hold an area of liquid (eg liposomes).
The largest version is the typical bilayer
Micelle
Liposome

7. Role of Proteins
Channel (pore) proteins – allow specific molecules and ions to pass through the membrane (by passive transport).
Carrier (pump) proteins – temporarily bind to specific molecules or ions, enabling them to cross the membrane (by active transport).
Enzymes – some proteins in the membrane catalyse a specific reaction. They are often activated by binding of a signal molecule on the outside

9. Extracellular liquid (outside of cell)
e.g. pore
Glycoprotein – often antigenic markers
Hydrophobic section of membrane
Phospholipid bilayer
Integral protein
transmembrane protein
Peripheral protein
Intracellular liquid (inside of cell)

10. Role of protein pores
Larger molecules depend on certain protein molecules to allow them to move across the membrane.
These transport proteins contains pores or channels.
These channels only allow specific substances to diffuse across the membrane.

11. Sodium/potassium pump
Certain protein on the cell membrane act as carrier molecules which transfer specific ion across the membrane.
These proteins are sometimes called pumps.
They can have a dual role, e.g. the sodium/potassium pump actively pumps sodium ions out of the cell and potassium ions into the cell, both against their own concentration gradient.

12. Conditions required by protein pumps…
The active transport of molecules across the membrane requires energy from respiration.
Therefore what conditions will affect the rate of active transport?