1. Membrane Structure and Function

2. Membrane Models
1925 Gorter and Grendel – extracted phospholipids from rbc’s, noted enough for bilayer, hydrophobic tails, hydrophilic heads
1940’sDanielli and Davson – sandwich model, phospholipids between 2 layers of proteins
Robertson- Unit membrane model
1972 – Singer and Nicolson – Fluid Mosaic model, proteins are partially or wholly embedded in irregular pattern

3. Plasma Membrane Structure and Function
Functions to separate and regulate = homeostasis
Phospholipids – polar heads, non-polar tails
Cholesterol – lipid in animal membranes, regulate fluidity, stiffens and strengthens

4. Membrane proteins
Peripheral – inside surface, held by cytoskeleton, structural role, stabilize and shape membrane
Integral – embedded in membrane, can move laterally back and forth
Transmembrane – have hydrophilic and hydrophobic ends, span entire membrane
Glycolipids – phospholipids with a carb chain attached
Glycoproteins- carbs on proteins

5. Carbohydrate Chains Carbohydrate chains – only on outside of membrane
Glycocalyx – “sugar” coating outside cell in animal cells – protection, adhesion between cells, cell recognition, reception of signal molecules
Basis for blood types in humans
Plays role in tissue rejection

6. Fluidity of Membrane Body temperature – consistency of olive oil
Fluidity dependent on lipid components
Critical to proper functioning
Proteins tend to drift laterally

7. Function of integral proteins
Each membrane has its own set of proteins, according to its function
Channel – passage of molecules and ions
Carrier – passage of molecules by combining with protein and being carried across membrane ex. Na+, K+, selective
Cell recognition – glycoproteins, recognize pathogens, stimulates immune system
Receptor proteins – have specific shape for specific molecule to bind. Ex. Signal molecules (hormones)
Enzymatic – carry out metabolic reactions directly

8. Plasma Membrane
Selectively, semi, differentially permeable – only certain substances can move across.
Free passage = passive transport
Need assistance
can be passive via a carrier protein
need energy = active transport

9. Passive transport
Water, small, non charged molecules (carbon dioxide, oxygen, glycerol and alcohol)
Move from a high concentration to a low concentration, following their concentration gradient
Carrier proteins – glucose and amino acids, specific for substance it carries (ions and polar molecules)

10. Diffusion
Movement of molecules, high to low until equilibrium is reached
Gases can diffuse through the lipid bilayer
Solution – solvent and solute
Once equilibrium is met, still move, but not in any one direction

11. Osmosis
Movement of water across selectively permeable membrane due to concentration differences
Osmotic pressure – pressure that develops in a system due to osmosis.

12. Tonicity Tonicity – strength of solution
Isotonic solution – equal concentrations of solute and water
.9% of NaCl solution is isotonic to rbc
Hypotonic solution – solution with lower concentration of solute than in cell
Water will follow solute and go in cell,
Animal cell – cytolysis, hemolysis
Plant cell – turgor pressure

13. Tonicity cont.
Hypertonic solution – more solute in solution than in cell
Animal cells – cell shrink – rbc’s - crenation
Plant cell – plasmolysis
Animals have built in osmoregulators that allow them to lose salt/water when needed.

14. Carrier proteins
Only carry specific molecules or ions across the membrane
Facilitated diffusion – helping, no energy ex. Glucose and amino acids.

15. Active Transport Accumulate, low to high concentration
Carrier proteins and ATP are needed
Usually find a lot of mitochondria near these membranes
Pumps – sodium-potassium pump, Na out, K in
Cystic fibrosis – faulty chloride channel

16. Vesicle formation Transport of macromolecules Uses energy Exocytosis
Golgi body produces vesicles, fuses with membrane, materials (hormones…) released outside of cell
Part of cell growth

17. Endocytosis Take in substances by vesicle
Membrane invaginates, pinches off, intracellular vesicle
Phagocytosis – large molecules, food, another cell ex. Wbc, amoeba
Pinocytosis – small molecules, liquids
Receptor mediated endocytosis - specific

18. Modification of cell surface Animal cells
Animal cells have junctions between their cells
Anchoring junctions
Mechanically attach adjacent cells
Adhesion junctions – intercellular filaments
Desmosome – single point of attachment, common in skin cells
Sturdy but flexible connection
Tight junctions
Proteins from plasma membrane attach to each other, zipper like
Ex. Barrier tissues, intestines, blood brain barrier

19. Junctions cont. Gap junction Allows cellular communication
2 identical channel proteins join
Strengthens membrane, allows small molecules and ions to pass

20. Extracellular matrix Nonliving network of polysaccharides and proteins
Collagen, elastin, fibronectins and laminins
Cartilage (gel), bone (solid)

21. Plant cells Cell wall Primary (cellulose fibrils)
Middle lamella – layer of adhesive substances, holds cells together.
Secondary wall – only in few plant cells, forms inside the primary cell wall
Plasmodesmata – membrane lined channels, connects cytoplasm of plant cells