Cell membrane F211

Cell F211

Membranes

Roles of membranes within cells and at the surface of cells;

• Separate cell contents from the outside environment

• Separate cell components from the cytoplasm

• Cell recognition and signalling

• Holding the components of some metabolic pathways in place

• Regulating the transport of materials into or out of cells

Plasma membranes are partially permeable barriers

The fluid mosaic model of membrane structure is a bilayer of phosopholipid molecules that forms the main structure. Various proteins are studded in the bilayer. Some are partially embedded (extrinsic) whereas some go all the way through the membrane (intrinsic).

Roles of the components of the cell membrane;

Phospholipids,

Have a hydrophilic phosphate head head and a hydrophobic fatty acid tail. They form a bilayer separating the cell from the outside. They are fluid so components can move around freely. They are partially permeable to allow small and/or non-polar molecules through, but impermeable to large molecules and ions.

Cholesterol,

Gives the membranes mechanical stability by sitting between fatty acid tails and therefore making the barrier more complete, preventing molecules like water and ions from passing through the membrane.

Glycolipids,

Phosopholipid molecules that have a carbohydrate part attached. They are used for cell signalling, cell surface antigens and cell adhesion.

Proteins,

Channel proteins allow the movement of some substances, such as the large molecule sugar, into and out of the cell as they can’t travel directly through the cell surface membrane. Carrier proteins actively move substances across the cell surface membrane.

Glycoproteins;

Phospholipid molecules with a protein attached. Same functions as glycolipids.

Effect of changing temperature on…