MEMBRANE STRUCTURE

MEMBRANE STRUCTURE

AND FUNCTIONS

MICRO LESSONRaquel Spencer

The Fluid Mosaic Model

This model proposes that membranes are not rigid, with molecules locked into place

Membranes consist of lipid molecules in which proteins are embedded and float freely.

The cell membrane is made of different parts working together, like a mosaic, made of many tiles of proteins

The lipid and protein molecules are generally free to move laterally within the two layers

Glycolipid

Carbohydrate group

Peripheral Protein

Phospolipid Bilayer

Transport Protein (integral)

Cholesterol

Integral Protein

The Role Phospholipids

THE HEADpolar = hydrophilic Interacts with water on the outside of the cell

Phosphate

Glycerol

THE TAILSnon-polar = hydrophobic Repelled by water, forced to face the interior of the cell

Saturated fatty acid

UNsaturated fatty acid

A bilayer forms spontaneously in an aqueous environment because of the tendency of the non-polar hydrophobic fatty acids to aggregate together while the polar heads associate with water.

Fluidity

Influenced by:

• Position of lipids molecules
• Temperature

Max. # Hydrogens = linear chains More rigid

Fewer HydrogensMore C=C

Hydrophilic end

Hydrophobic end

Hydrophobic Tail

The role of Membrane Proteins

Functional categories:

Transport

Enzymatic activity

Membranes are not designed for free diffusion of substances, but specific compounds can cross them through hydrophilic protein channels or shape shifting membrane proteins.

Some membrane proteins, such as those associated with respiration and photosynthesis, are enzymes.

Functional categories:

Attachment & Recognition

Triggering signals

Proteins exposed to membrane surfaces serve as attachment points for cytoskeleton elements, cell-cell recognition components, and bond to the extracellular matrix, enabling them to recognize disease-causing microbes and trigger an immune response.

Membrane proteins may bind to specific chemicals, such as hormones. Binding to these chemicals triggers changes on the inner surface of the membrane, starting a cascade of events within the cell.