9/26 - Biological Membranes

Roles of biological membranes

• separates cells from external environment

• maintains control of cell shape

• controls passage of materials in and out of cell

• membranes contain enzymes & other molecules

• allows transduction of cell signals

Why are membranes important in pharmacy?

bioavailability of drugs influence its ability to cross cell membranes

3 major chemical components of biological membranes

lipids, proteins, and carbohydrates

What membrane component is the framework for all membranes?

lipids

What membrane component usually accounts for the largest portion?

proteins

Roles of lipids in membranes

double bonds in unsaturated FAs produce kinks

How does the length of lipids affect fluidity?

shorter length = higher fluidity

Lipid bilayer forces

amphipathic, held in formation via hydrogen bonds & van der waals forces

In what order are specific lipid types most abundant in membranes?

1. glycerophospholipids

2. sphingolipids

3. cholesterol

Protein membrane functions

channels, transporters, receptors, enzymes, regulatory proteins, anchoring proteins, structural proteins

Carbohydrate functions

protection, recognition of signals & markers, cell adhesion, defense against disease

Factors affecting lipid bilayer

lipid composition and temperature

Affect of temperature of lipid bilayer fluidity

higher temp, higher fluidity

Integral proteins

inserted into membrane and can fully or partially penetrate the membrane

Peripheral proteins

attached to the membrane through weak electrostatic interactions, attached to the head groups of phospholipids or with an integral membrane protein

Lipid-anchored proteins

covalently attached to fatty acid acyl chains from the lipid membrane or to peripheral proteins

Effect of cholesterol on membranes

disrupts hydrophobic interactions between fatty acyl tails and effects temp

Effect of higher temp on fluidity when cholesterol is added

decreases fluidity

Effect of lower temp on fluidity when cholesterol is added

higher fluidity, prevents freezing

Liquid crystal state

hydrocarbon chains of phospholipids are disordered and in constant motion

Liquid crystal state transition temp vs. crystalline state transition temp

liquid crystal: higher; crystalline: lower

Lipid rafts

sub compartments of the plasma membrane with different lipid and protein composition

Components of lipid rafts

sphingolipids, cholesterol

Roles of antidepressants when interacting with lipid rafts

G proteins that activate adenylyl cyclase are released from lipid rafts, increasing cAMP production