BIOL 300 Exam 3

Three essential functions of the membrane

1. Receiving information - sensors for receiving information (receptors)

2. Import and export of molecules - channels and pumps

3. Capacity for movement and expansion - cytoskeleton and adding new membrane

Benefits of cell compartments (organelles)

Allows chemical reactions to be separated from each other

Protects vital structure (DNA)

Liposomes

Just pure phospholipids added to water

An artificial bilayer created in labs

Used in pharmacy for nano drug delivery systems

Types of phospholipid movements

Lateral diffusion ←→

Flexion - moving of tails

Rotation - spinning of a phospholipid

Flip-flop - switching side of the membrane (requires flipase proteins and energy) RARELY OCCURS

Lipid rafts

Specialized membrane microdomains that compartmentalize cellular processes by serving as organizing centers for the assembly of signaling molecules, influencing membrane fluidity and membrane protein trafficking and refulating neurotransmission and receptor trafficking.

Different types of membrane lipids and their roles

ALL amphipathic

Phosphatidylcholine - Most common, mainly structural, found on outside

Sphingomyelin - Myelin sheathing, mostly outside, signaling

Phosphatidylserine - Found on inside, flips to outside during apoptosis

Phosphatidylethanolamine - Found on inside, involved in membrane fusion

Glycolipids - Provides energy, acts as cell surface marker

Cholesterol - Maintain fluidity and structure on the membrane

Galactocerebroside - Stabilizes myelin sheathing

Inositol phospholipids - Important signaling molecules

Bilayer synthesis

Occurs in the ER

New membrane exported to other membranes by budding and fusion

Bilayer pinches off from ER to form vesicles which can then be incorporated into another membrane by fusing with it

Types of membrane proteins - based on function

Transporters

Anchors

Receptors

Enzymes

Ion channels

Types of membrane proteins - Based on association with lipid bilayer

Transmembrane

• Amphipathic

• alpha helix

• beta pleated sheets (beta barrel)

Monolayer-associated

• Amphipathic alpha-helix exposed on the surface of the membrane

Lipid-linked

• Lie entirely outside of the bilayer

• On the cytosolic or extracellular side

• One or more covalently bound lipid groups in the membrane

Protein-attached

• Bound indirectly by interactions with other membrane proteins

• One or the other face of the membrane