Cell Membrane & Extracellular Matrix

Lecture 14

Fluid Mosaic Model

the plasma membrane is composed of lipids, proteins, and carbs

Cholesterol

a temperature mediator; prevents too much fluidity or solidification of the phospholipid bilayer

What moves laterally and what drifts within the phospholipid bilayer?

Lipid molecules move laterally and proteins drift across the phospholipid bilyaer.

Glycoproteins & Glycolipids

• carbs added to proteins and lipids; faces the extracellular (outer) surfaces

• acts as an “ID tag” for cell recognition

Integral (Transmembrane) Proteins

spans the entire bilayer; amphipathic (fluid movement) with the hydrophobic tails

Peripheral Proteins

loosely bound to the inner or outersurface

What are the 6 major functions of membrane proteins?

1. Transport across the membrane

2. Catalyzes reactions (enzymatic)

3. Relays external signals

4. Recognizes neighboring cells

5. Forms junctions between cells (adhesion)

6. Attaches the cytoskeleton to the ECM

How do saturated vs unsaturated fatty acids affect membrane fluidity?

Saturated fatty acids decreases fluidity.
Unsaturated fatty acids increase fluidity.

Passive Transport

no-energy movement along a concentration gradient

Active Transport

ATP moves substances against the concentration gradient

Aquaporins

channel proteins that allow rapid water passages across membranes

Plasmodesmata

(in plants) opening in the cell walls so small molecules/ions can pass through

Tight Junctions

(in animals) seals neighboring cells, preventing leakage

Gap Junctions

(in animals) opening in the cell walls so small molecules/ions can pass through

Desmosomes

(in animals) anchors cells together by connecting their intermediate filaments

Extracellular Matrix (ECM) (structure)

*ONLY IN ANIMALS*

composed of collagen fibers in a web of proteoglycan complexes

Extracellular Matrix (ECM) (function)

• support

• adhesion

• communication

Integrins

cell surface’s receptor proteins

• anchors the cytoskeleton (microfilaments) to the ECM

• transmits signals

• influences gene expression and movement

Fibronectin

connects the ECM to integrins