1. BUBBLES!! MUST wear goggles at ALL times!
NO taking straw out of the dish!
NO drinking/ inhaling bubble fluid
THIS IS an EXPERIMENT!!!
You can have fun, but ALL usual lab safety RULES APPLY!

2. Questions to think about:
Can anything pass through the bubble without breaking it?
Can one bubble divide to become several bubbles?
Can several bubbles merge to form one- how?
Can a drop of water pass through a bubble without popping it?
Does it look like the surface of the bubble moves? How can you tell?

3. soapy “membranes”
1. How does a bubble model the fluid nature of a membrane?
2. Can anything pass through the membrane without rupturing it? If so what; if no, what did you try?
3. Can one bubble divide to become several bubbles?
4. Can several bubbles merge to become one bubble?
5. Can a drop of water pass through a bubble without popping the bubble?
6. A bubble is a lipid monolayer – draw a diagram of a segment of a bubble using this symbol for a lipid molecule:

4. Bubble Summary! A bubble is a lipid monolayer!!
What is the structure of the membranes of our cells?
How does a bubble model the fluid nature of a cell membrane?

5. L3 Biology Chapter 4 CELL MEMBRANES and TRANSPORT

6. The Cell

7. Learning Objectives
Describe the fluid mosaic model of membrane structure and explain the underlying reasons for this structure.
Outline the roles of phospholipids, cholesterol, glycolipids, proteins and glycoproteins in membranes.
Outline the roles of the plasma membrane, and the roles of membranes within cells.

8. Plasma Membrane (aka Cell Membrane)
All living things are surrounded by a membrane.
It controls exchange of materials (like nutrients, waste) between cells and the environment.
Other important functions include:
communicate to other cells
respond to hormones.
To understand FUNCTION in BIOLOGY, you must first study STRUCTURE!

9. Cell Membranes from Opposing Neurons (TEM x436,740).
Nerve cell
Gap between cells
Cell membrane { }
cell membrane
Is 7nm wide
Nerve cell

10. Remember our discussion of our favorite POLAR Molecule?
WATER!
Due to unequal distribution of electrons (electronegativity of Oxygen), one end of molecule is partially positive while other end is partially negative. The molecule has ‘poles’
WATER is the solvent inside and outside every cell.

11. Phospholipids are the Primary Building block of the membrane:
HYDROPHILIC heads (water loving) -Attracted to the water
called POLAR head
HYDROPHOBIC tails (water fearing) -Not attracted to the water
called NON-POLAR Tails.

12. PHOSPHOLIPIDs are AMPHIPATHIC molecules with both POLAR AND NONPOLAR regions
Which atoms/regions are Polar?
Which atoms/regions are nonpolar?

13. Why does the phospholipid have a Hydrophilic Head?
One end of the phospholipid has a phosphate group and several oxygens atoms that are not shared equally. This end of the molecule has a charge and is attracted to water. It is POLAR!
3D model of a Phospholipid

14. Why does the phospholipid have Hydrophobic tails?
Two long chains (tails) at bottom of phospholipid made up of carbon and hydrogen. Both these elements share their electrons evenly, so there is no charge (NON POLAR). They are not attracted to water; water molecules tend to push them out of the way as they are attracted to another H2O. These molecules do NOT dissolve in water.
3D model of a Phospholipid

15. How does the Plasma Membrane form?
Phospholipid tails interact AWAY from the water, and the heads associate with the water of the solution and cytoplasm -The result is 2 layers of phospholipids with hydrophobic tails protected inside the membrane by the hydrophilic heads.
Lipid BILAYER, the MAIN structure of the Plasma Membrane

16. WATER Hydrophilic head Hydrophobic tail WATER Figure 7.2
Figure 7.2 Phospholipid bilayer (cross section). 16

17. Properties of Cell Membranes
Basic structure is Phospholipid Bilayer.
Phospholipids move laterally within the membrane.
Composition of Phospholipid fatty acid tails can be Saturated (straight) or Unsaturated (bent) depending on the organism & environmental conditions (ie temperature)

18. Phospholipids move within the membrane:
Lateral movement occurs 107 times per second.
Flip-flopping across the membrane is rare ( once per month).
Figure 7.6 The movement of phospholipids. 18

19. Unsaturated hydrocarbon tails Saturated hydrocarbon tails
Figure 7.8
Fluid
Viscous
Unsaturated hydrocarbon tails
Saturated hydrocarbon tails
(a) Unsaturated versus saturated hydrocarbon tails
(b) Cholesterol within the animal cell membrane
Figure 7.8 Factors that affect membrane fluidity.
Cholesterol 19

20. Animation of membrane formation

21. Why is the Plasma Membrane necessary?
Provide containment for the cell structures
Phospholipids are PRIMARY component that forms the membrane
Phospholipids protect the cell from environmental hazards by acting as a barrier to most water soluble substances
BUT, Phospholipids are only PART of the story of the plasma membrane…………

22. Diagram (model) representing the cell membrane Remember the membrane is 7nm wide

23. Models in Biological Systems:
A Model is a HYPOTHESIS:
A visual representation of an abstract concept or minute molecules
A way to manipulate and perform a biological process

24. What are 2 important points of Models:
Accuracy in representing the concept, molecules or process
Precision in the details of the representation

25. Models to represent Biological Systems:
Replacing 1 model for another does NOT imply first was worthless
Acceptance or rejection of model depends on how well it
Fits observations
Explains experimental results
New findings may result in revision of model or development of NEW model
New model MAY incorporate some properties of old model

26. Their model was named the Fluid Mosaic Model.
In 1972, S. J. Singer and G. Nicolson proposed that the membrane is a mosaic of proteins dispersed within the bilayer, with only the hydrophilic regions exposed to water
Their model was named the Fluid Mosaic Model.
© 2011 Pearson Education, Inc.

27. Phospholipid bilayer Hydrophobic regions of protein
Figure 7.3
Phospholipid bilayer
Figure 7.3 The original fluid mosaic model for membranes.
Hydrophobic regions of protein
Hydrophilic regions of protein 27

28. Current Model of the Cell Membrane
Fibers of extra- cellular matrix (ECM)
Glyco- protein
Carbohydrate
Glycolipid
EXTRACELLULAR SIDE OF MEMBRANE
Figure 7.5 Updated model of an animal cell’s plasma membrane (cutaway view).
Cholesterol
Microfilaments of cytoskeleton
Peripheral proteins
Integral protein
CYTOPLASMIC SIDE OF MEMBRANE 28

29. Fluid mosaic model!!
Cell membranes also contain cholesterol and proteins within the phospholipid bilayer.
This ‘model’ for the structure of the membrane is called the: FLUID MOSAIC MODEL

30. Why call it a Fluid Mosaic Model?
FLUID- because phospholipids and proteins move around freely within the layer, like it’s a liquid. MOSAIC- because of the pattern produced by scattered protein molecules in the membrane when viewed from above.

31. Animation of membrane formation

32. Remember Cholesterol (Lipids)

33. What is the function of cholesterol?
Cholesterol regulates the fluidity of the membrane, gives mechanical stability and help to prevent ions from passing through the membrane.

34. Cholesterol between the phospholipid tails

35. Proteins determine most of the membrane’s specific functions
Where are the proteins?
Integral membrane proteins: Integrated in the membrane with access to both cytoplasm and outside cell
Peripheral membrane proteins: Facing only the cytoplasm OR outside the cell as part of one side of the membrane
Proteins can float or be fixed:
- Like phospholipids, many of them have hydrophobic and hydrophilic regions
Proteins determine most of the membrane’s specific functions

36. Individual Proteins serve different functions:
1. Proteins act as channels for substances to move in or out of cell.
2. Proteins act Pumps to move molecules across the membrane.
3. Proteins act as membrane enzymes in chemical reactions.
4. Proteins help to stabilize the membrane

37. Some proteins have sugars attached
These are called Glycoproteins
What is their function?
Glycoproteins act as markers for cell communication, antigens for other cells to recognise them, or receptors that hormones & other proteins can bind.

38. Membrane with protein

39. Summary
Cell membranes have a basic structure composed of a PHOSPHOLIPID BILAYER.
Phospholipds have HYDROPHOBIC (non-polar) tails and HYDROPHILIC (polar) heads.
The best model of the cell membrane is called the FLUID MOSAIC MODEL
The average thickness of the membrane is 7nm.

40. Summary, cont.
The fatty acid tails of phospholipids can be SATURATED (straight) or UNSATURATED (bent)
Phospholipids form the bilayer, act as barrier to most water soluble substances
Cholesterol regulates the fluidity of the membrane, gives mechanical stability and help to prevent ions from passing through the membrane.

41. Summary, cont.
Proteins determine specific properties of the membrane (Key to Cell differentiation!)
Proteins are integrated or peripheral:
float or fixed in the membrane
also have hydrophobic and hydrophilic portions.
Proteins function in:
Transport- channels for substances to move in or out of cell
Enzymes
Pumps
Membrane stabilizers

42. Summary, cont.
Some proteins have carbohydrates attached to them to form GLYCOPROTEINS .
Glycoproteins act as receptor molecules (eg for hormones and neurotransmitters), as antigens for cell recognition, as markers for cell communication.

43. Visualizing structure and function

44. Do it yourself- build a membrane!
Go to this website on the notepads, and follow directions to build a membrane!

45. (Hint-Is it ever the same??)
Wrap-up!
How is the cell’s membrane structured (chemically) to ensure efficiency, survival, & differentiation?
(Hint-Is it ever the same??)

46. Preview of coming attractions!
Membrane structure allows for the movement of substances into and out of the cell
Living organisms demonstrate many adaptations to their membranes allowing them to survive in their environments!

47. Movement of selected molecules across the cell membrane

48. Moving amoeba
Contractile vacuole

49. Functions of Cell Membrane Components:
Use the following headings to produce a table summarizing the functions of the different types of molecules found in the cell membrane. Use your notes to find the information.
Component Structure Functions
Phospholipids
Cholesterol
Proteins
Glycoproteins