1. 1.3 Cell membrane structure and function
IB Biology

2. I can understand that…
Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules.
Membrane proteins are diverse in terms of structure, position in the membrane, and function.
Cholesterol is a component of animal cell membranes.

3. Prison fence? How does that relate?
Entry-way only accessible to the special guards
Outside fence
Inside fence
Outside environment

4. Biological membranes Separate the cell from the environment
Allows some substances to move across more easily than others
Has 2 layers (bilayer)
Helps maintain homeostasis
Protective Barrier
Allows cell recognition
Provides binding sites for enzymes
Bind cells together in interlocking junctions
Contains cytoplasm

5. Cell membrane Phospholipid bilayer ~8 nm thick Selectively permeable
Flexible
Fluid Mosaic Model

6. Structure of the cell membrane: phospholipid bilayer

7. Amphipathic phospholipid layers
Amphipathic (adj.): Pertains to a molecule containing both polar (water-soluble) and nonpolar (not water-soluble) portions in its structure. (biology-online.org)

8. Phospholipids Made up of: Glycerol 3-carbon compound Water soluble
Phosphate group
2 fatty acid chains
Not water soluble because they are non-polar
Hydrophilic Head Water Loving
Hydrophobic Tail Water Fearing
The hydrophobic and hydrophilic regions make the phospholipids line up as a bilayer

9. Models of the cell membrane
Davson-Danielli Model:
Singer-Nicolson “Fluid Mosaic Model”

10. Fluidity of the membrane
Cholesterol in the tail-region of membrane
Stabilizes fluidity, which changes with temperature
Less fluid in warmer temperature by restraining phospholipid movement
More fluid in colder temp by preventing close packing of phospholipids
Flip-Flop and Lateral Movement of phospholipids in the membrane
Flippase?
Unsaturated (kinks) enhance fluidity
Saturated phospholipids make membrane easier to solidify

11. Proteins of the membrane
Integral Proteins:
Have an amphipathic character
Completely penetrate the lipid bilayer
Control the entry and removal of specific molecules from the cell

12. Proteins of the membrane
Peripheral Proteins:
Remain bound to the surface of the membrane
They are often anchored to an integral protein

13. Selective permeability
Some non-polar substances are transported directly through the lipid bilayer.
Smaller non-polar molecules move faster than larger ones.
Some polar substances, particularly ions and carbohydrates, are transported across the membrane via the channel proteins.
Some smaller, uncharged polar substances go right between the phospholipids into the cell.
Selective Permeability

14. Functions of membrane proteins
Pumps for active and passive transport
Cell adhesion
Enzymatic action
Cell-to-cell communication
Sites for hormone binding

15. Transport proteins + Passive transport

16. Questions?
Answer the following questions in your notes guide then share with a partner:
Explain the orientation of the bilayer of phospholipid molecules in the plasma membrane using the terms ”hydrophobic” and “hydrophilic”. Draw a sketch of the bilayer.
What type of properties do amphipathic phospholipids have?
What types of substances can pass directly through the membrane.
What is the function of cholesterol in the plasma membrane?
1.Hydrophilic heads and hydrophobic tails in a bilayer.
2. Both hydrophobic and hydrophilic regions.
3. Non polar substances
4. Helps stabilize the membrane, without cholesterol the membrane would be too fluid and let too many substances through.

17. I understand that…
Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules.
Membrane proteins are diverse in terms of structure, position in the membrane, and function.
Cholesterol is a component of animal cell membranes.

18. Source
Damon, Alan, Randy McGonegal, Patricia Tosto, and William Ward. "1.3 and " Higher Level Biology. 2nd ed. N.p.: Pearson Education Limited, n.d. N. Print.