1. CELL Membranes

2. Competencies
1. describe the structural components of the cell membrane- STEM_BIO11/12-Ig-h-11
2. relate the structure and composition of the cell membrane to its function - STEM_BIO11/12
-Ig-h-12

3. Activity (10 mins)
Q & A
1. What do you remember about Cell membrane? Describe the membrane
2. Differentiate Plant and Cell membranes?
3. What are common substances impregnated in Cell membrane and what are its functions?

4. Cell Membrane (Transport) Notes
Cell Membrane and Cell Wall:
ALL cells have a cell membrane made of proteins and lipids
Cell Membrane
lipid bilayer
protein channel
protein pump
Layer 1
Layer 2
SOME cells have cell membranes and cell walls – ex: plants, fungi and bacteria
Cell Membrane
Cell Wall

5. Plant cells have a cell wall made of cellulose – that cellulose is fiber in our diet
Bacteria and fungi also have cell walls, but they do not contain cellulose
Cell membranes and cell walls are porous allowing water, carbon dioxide, oxygen and nutrients to pass through easily

6. CO 5

7. Membrane Structure
The fluid mosaic model of membrane structure has two components:
1. Phospholipids arranged in a bilayer
2. Globular Proteins inserted in the lipid bilayer

9. Membrane Structure Cellular membranes have 4 components:
1. Phospholipid Bilayer
2. Transmembrane Proteins
3. Interior Protein Network
4. Cell Surface Markers

11. Membrane Structure
Membrane structure is visible using an electron microscope.
Transmission electron microscopes (TEM) can show the 2 layers of a membrane.
Freeze-fracturing techniques separate the layers and reveal membrane proteins.

12. Fig

13. Fig

14. Fig

15. Fig

17. 1. Phospholipids Phospholipid Structure (Chapter 3)
-glycerol – a 3-carbon polyalcohol acting as a backbone for the phospholipid
-2 fatty acids attached to the glycerol
-phosphate group attached to the glycerol

18. 1. Phospholipids
The fatty acids are nonpolar chains of carbon and hydrogen.
-Their nonpolar nature makes them hydrophobic (“water-fearing”).
-The phosphate group is polar and hydrophilic (“water-loving”).

19. 1. Phospholipids
The partially hydrophilic, partially hydrophobic phospholipid spontaneously forms a bilayer:
-fatty acids are on the inside
-phosphate groups are on both surfaces of the bilayer

21. 1. Phospholipids Phospholipid bilayers are fluid:
Hydrogen bonding of water holds the 2 layers together
Individual phospholipids and unanchored proteins can move laterally through the membrane

22. 1. Phospholipids Phospholipid bilayers are fluid:
Saturated fatty acids make the membrane less fluid than unsaturated fatty acids
Cholesterols make the membrane more rigid
Warm temperatures make the membrane more fluid than cold temperatures

23. Fatty Acids 87

24. Lipids: Cholesterol Figure 2.22 H3C CH3 CH3 CH3 CH3 HO 2-83
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H3C
CH3
CH3
CH3
CH3 HO
Figure 2.22
2-83

26. Fluid Mosaic Model

27. 2. Membrane Proteins Membrane proteins have various functions:
1. Transporters
2. Enzymes
3. Cell Surface Receptors
4. Cell Surface Identity Markers
5. Cell-to-Cell Adhesion Proteins
6. Attachments to the Cytoskeleton

29. Membrane Proteins Two types of membrane proteins
Classified by how they are associated with the membrane
Peripheral membrane proteins
Integral membrane proteins

30. Membrane Proteins 1. Peripheral membrane proteins
Anchored to a phospholipid in one layer of the membrane
on the intracellular or extracellular face of the membrane
Oossess nonpolar regions that are inserted in the lipid bilayer
Free to move throughout one layer of the bilayer

31. 1. Peripheral membrane proteins

32. Membrane Proteins 2. Integral membrane proteins
Span the lipid bilayer (transmembrane proteins)
Nonpolar regions of the protein are embedded in the interior of the bilayer
Transmembrane Domain
Polar regions of the protein protrude from both sides of the bilayer

33. 2. Integral membrane proteins

34. Membrane Proteins
Integral proteins possess at least one transmembrane domain
Region of the protein containing hydrophobic amino acids
Spans the lipid bilayer
Usually alpha-helices
Many receptors are integral proteins

36. Membrane Proteins
Extensive nonpolar regions within a transmembrane protein can create a pore through the membrane.
β sheets in the protein secondary structure form a cylinder called a β-barrel
β-barrel interior is polar and allows water and small polar molecules to pass through the membrane

38. Membrane Transport Passive Transport Active Transport
Motion of substances in and out of the cell
Cell membranes are Selectively permeable
Two Types of Transport Mechanisms:
Passive Transport
Active Transport

39. Membrane Transport
Passive transport is movement of molecules through the membrane in which no energy is required from the cell
Active transport requires energy expenditure by the cell

40. Video on Cell membrane and Cell Transport
Guide Questions:
1. What is cell membrane and its composition based on the video?
2. Initially, what is Cell Transport? Describe each type.