1. Chapter 7.1 – 7.2 Cellular Biology
Cell Membrane
Chapter 7.1 – 7.2
Cellular Biology

2. What you need to know! Why membranes are selectively permeable.
The role of phospholipids, proteins, and carbohydrates in membranes.

3. Plasma Membrane (PM)
Barrier between interior and exterior (of animal/plant cells and organelles)
Maintains homeostasis
Allow for compartmentalization (eukaryotes)
PM is selectively permeable for gases, H2O, entering nutrients, exiting waste, etc.
Blocks harmful substances and microorganisms
Made of primarily of phospholipids and proteins

4. Phospholipids Phospholipids form a bilayer in aqueous solutions
the heads (phosphate groups) are polar (hydrophilic) and will form the two outer faces
the fatty acid tails are hydrophobic and point toward the inside

5. Fluid Mosaic Model Structure can be observed with EM
Mosaic of floating phospholipids with cholesterol, proteins, glycoproteins, and glycolipids embedded
Held together by hydrophobic/hydrophilic interaction and cytoskeleton attached to desmosomes.
Flexible and in constant motion
Think of a soap bubble skin rather than saran wrap

6. Fluidity: Phospholipid molecules move around constantly
Fluidity regulated by different kinds of fatty acid (FA) tails:
More unsaturated FA, membrane stays fluid at lower temp (winter)
More saturated FA, membrane is more stable at high temperatures (summer)
Cholesterol embedded in animal membranes also maintains fluidity

7. Membrane Molecules
Integral – proteins that are embedded in the bilayer
contain hydrophilic ends and hydrophobic mid-sections to mimic the phospholipids
Transmembrane proteins span the entirety of the bilayer (stick out on both ends)
Peripheral proteins: not embedded but loosely attached (usually to integral proteins)

8. Transmembrane Proteins
Transport
Enzymatic
Signal transduction
Cell-cell recognition
Intercellular joining
Attachment to the cytoskeleton and extracellular matrix (ECM)

9. Membrane Molecules
Peripheral Proteins loosely connected on only one side of the membrane
Membrane bound pigments in plants
Chlorophylls
Carotenoids
Both sides of the membrane are not identical:
Cytoplasmic side
Extracellular side
Animals: Extracellular Matrix (ECM)
Glycoproteins = carbohydrates attached to proteins for self recognition/immune system
Collagen fibers for connectivity
Plants: Cell wall (1st, middle lamella, 2nd)

10. Intercellular Connections:
Animals:
Tight Junctions: allowing movement of material across cell layer/preventing movement of material between cells: digestive system, epithelial cells
Desmosomes: tight connection of adjacent cells under high physical stress (muscle, cartilage), attached to cytoskeleton
Gap-Junctions: intercellular ion and small molecules transfer

11. Intrercellular Connections:
Plants have Plasmodesmata: channels between plant cells where ER goes through (desmotubule)