Fluid Mosaic Model

Cell Membrane permeability

• Is a selectively permeable or semi-permeable membrane, meaning it regulates the movement of substances.

• The membrane allows some substances through more easily than others, with small pores or channels transporting particular substances.

• Allows some substances in (or out) and not others.

Models in Science

• Is a representation of a system or phenomenon

• Are always changing with new evidence, new questions

• Used to explain how things work, make predictions of expected results, simplify concepts, visually represent something that cannot be seen.

• Model selection is important to get valid and reliable results. A model that is makes innacurate predictions will be revised or replaced.

• Models need to be validated in order to be accepted. Limitations should be documented.

The fluid mosaic model of the cell membrane

• Fluid - the phospholipid bilayer is viscous and individual phospholipids and some proteins can move laterally, allowing flexibility and self-repair.

• Mosaic - is a mosaic of components embedded with proteins within or attached to the phospholipid bilayer, resulting in a mosaic of components.

Components - Phospholipids

• The lipids (fats) in membranes are called phospholipids.

• In an aqueous (water environment) they form a bilayer arranged with phosphate heads facing outwards toward the cytoplasm and extracellular fluid and fatty acid tails facing inwards towards each other

• The phosphate heads are hydrophilic and polar (water-loving) and the fatty acid tails are hydrophobic (water-hating).

• This arrangement forms a stable barrier separating the internal and externa environments of the cell.

Components - Proteins

• Can be either integral (transmembrane) or peripheral and serve a variety of roles

• Proteins that are a temporary part of the cell membrane are called peripheral proteins. Integral proteins are permanent.

• Peripheral proteins will bond with integral proteins.

• When integral proteins span from one side of the bi-lipid layer to the other, they are called transmembrane proteins.

Components - Carbohydrates

• In the cell membrane, they are linked to protruding proteins and are referred to as glycoproteins.

• If attached to lipids they are called glycolipids.

• Carbohydrates enable cells to adhere to one another. They are important markers in cell recognition for antibodies.

Components - Cholesterol

• Is found in animal cell membranes

• Improves stability and reduces fluidity