1. Unit 3 – Membranes & Transport

2. Selectively Permeable
There are barriers separating cells and organelles (cell parts) from world around it
Plasma (Cell) Membrane
Each cell is a protected compartment
Boundary in/outside of cell
YET Liquid, changing, dynamic
Selectively Permeable
Some things can/cannot pass across membrane
Plasma Membranes are composed mainly of
Phospholipids, Proteins

3. Chemical Structure of a Plasma Membrane
PHOSPHOLIPID
Primary structure component
Modified Triglyceride
Phosphate group (PO4-3) replaces one of the three fatty acids normally found.
The addition gives:
Polar “head”
Two non-polar “tails”

5. Structure of the Lipid Bi-layer
Cell membranes are composed of 2 layers of phospholipids and protein
Lipids are main “fabric” of membrane
Proteins are “floating” in membrane
other amphipathic, organic compounds also floating
Amphipathic = Having both hydrophobic & hydrophilic end

6. Structure of the Lipid Bi-layer

8. This is the Fluid Mosaic Model of Lipid Bi-layers
Model of cell membrane structure; individually inserted proteins drifting laterally in fluid layer of phospholipids
Mosaic - Structure made up of many different parts
Lipid bi-layer forms because
Hydrophobic ends of molecules face inward
packed together away from water,
Hydrophilic ends face outward
toward the water

10. Helps maintain fluidity
Two factors maintain fluidity
Fatty Acid Tails
If phospholipids were SATURATED, non-polar tails would be…
Straight
If phospholipids were UNSATURATED, tails would be …
Kinked
Kinks in tails keep molecules from packing close together
Helps maintain fluidity

11. Fluidity Unsaturated/Polyunsaturated F.A. tails Cholesterol Non-polar
Serves as a blocker in the fatty acid tails

12. What does AMPHIPATHIC mean
What does AMPHIPATHIC mean? What are the two factors that affect fluidity? Describe the polarity of things that are Hydrophobic and Hydrophilic? What does it mean to be Selectively Permeable?

13. WEBPAGE

14. Fluidity means that Lipids can float around each
Fluidity means that Lipids can float around each other Different factors affect this…

15. Lipids can drift about randomly in the plane of membrane
Movement is vital to membrane function
Lateral, Rotate
Will NOT switch/flip-flop planes
Separates cell from the external environment AND regulate flow of materials in and out of cell

17. Selectively Permeable
Membrane has specific properties that allow things to pass through or not pass through -
CAN vs. CANNOT
Not all molecules are equally soluble in PM
Size
Polarity/Non-polarity
Charged/Uncharged

18. Selectively Permeable
Rules:
Small and/or hydrophobic (NP) pass VERY easily
Large and/or hydrophilic (polar) NOT easily
Permeable to many lipids, lipid-like substances, and gasses
Impermeable to such things as proteins and amino acids, nucleic acids, and carbohydrates

19. Permeability

20. Fluid Mosaic Model
To complete the F.M.M. – need to include the role of PROTEINS– Lipid bi-layer is a great model, but not complete story Need proteins to move Large, Charged, Polar Substances across membrane

21. Passive Transport High Concentration to Low Concentration
With/Down the Concentration Gradient
Does not requires energy (ATP)

22. Types of Passive Transport
Diffusion- movement of small, nonpolar, and /or uncharged molecules directly across the membrane.
EX: O2, CO2
Osmosis- diffusion of water directly across the membrane
Facilitated Diffusion- diffusion of larger, polar, and/or charged molecules across the membrane with the help of a transport protein.
EX: Amino Acids, monosaccharides, ions

23. Passive Transport

24. Integral Intrinsic Trans-membrane
Embedded in membrane
COMPLETELY spans membrane
Have Hydrophobic and Hydrophilic regions
70-80% of the proteins in membranes
Not easily extracted from membrane
Most often involved in transport / reception

25. Peripheral / Extrinsic
Proteins not embedded in lipid bi-layer
Appendages LOOSELY bound to surface of membrane
20-30%
Various roles
Enzyme activity, Signal transduction, intercellular joining, cell-cell recognition, ECM attachment

26. Roles / Functions Transport Channel Proteins – Non-selective Receptor
Gated Channel - Selective (Specific Ion/Molecule)
Carrier – Carries materials across
Receptor
Peripheral – Ex. : INSULIN
Antigens
Communication to immune system that cells belong
Membership card
If bacteria, virus, other; begin immune defense

27. Movement Proteins crucial portion of the membrane structure
Assist in movement of material through the membrane
Provide structure for the membrane

28. Active Transport Low Concentration to High Concentration
Against/Up Concentration Gradient
Requires Energy (ATP)
Used to keep high concentrations high and/ or low concentrations low (wastes)

29. Types of Active Transport
Active Transport with a transport Protein
EX: Ion Pump
Endocytosis/ Exocytosis
EX: huge molecules like proteins

30. Active Transport