The Structure and Function of the Plasma Membrane Lecture5 The Structure and Function of the Plasma Membrane

Plasma membrane Only 5 to 10 nm wide The simplest bacteria have only a single membrane

MEMBRANE FUNCTIONS Compartmentalization Scaffold for biochemical activities Providing a selectively permeable barrier Transporting solutes Responding to external signals Intercellular interaction Energy transduction

Membrane Structure The lipids in cell membranes combine two very different properties in a single molecule: each lipid has a hydrophilic (“water-loving”) head and one or two hydrophobic (“water-fearing”) hydrocarbon tails.

Different type of membrane lipids

Liposomes as Potential Drug Carrier Systems for Drug Delivery

Membrane fluidity and its roles in the perception of environmental signals The fluidity of a cell membrane is important for membrane function and has to be maintained within certain limits. hyperosmotic stress reduce membrane fluidity similarly to low-temperature stress.

Asymmetry in membranes Cell membranes are generally asymmetrical Phosphatidylcholine and sphingomyelin are located primarily in the outer leaflet, while phosphatidylserine (PtdSer) and phosphatidylethanolamine (PtdEtn) are restricted to the cytoplasmic side. Scramblases non-specifically and bidirectionally transport phospholipids between the inner and outer leaflets in an ATP-independent manner, while flippases, also known as ATP-dependent aminophospholipid translocases, transport PtdSer and PtdEtn from the extracellular to the cytoplasmic side.

Membrane proteins

Membrane proteins associate with the lipid bilayer in Various Ways

Cell cortex

Membrane domains

Carbohydrate layer

Lipid Bilayers Are Impermeable to Solutes and Ions

Membrane Transport Proteins

Passive and Active Transport

Conformational change in a transporter

Electrochemical gradient

Active transport by three main ways

Na+/K+ pump

The Na+/K+ Pump Helps Maintain the Osmotic Balance of Animal Cells

Coupled transporters

Glucose–na+ symporters

Two types of glucose transporters in epithelial cell

H+ Gradients Are Used to Drive Membrane Transport in Plants, Fungi, and Bacteria

Aquaporins

Ion channels

Stress-gated ion channels allow us to hear