2. Functions of the plasma membrane 1.Holds the cell together 2.Controls what goes in and out (diffusion, osmosis, active transport) 3.Protects the cell 4.Allows the cell to recognize and be recognized (cell signaling and immunity) 5.Binds to other cells and molecules 6.A site for biochemical reactions (enzymes, areas for reactions)

3. 2.4.1 Plasma membrane diagram Components: 1.Phospholipids (are the major component of PM) 2.Proteins (integral and peripheral) 3.Other components (Cholesterol, glycoprotein…)

4. 2.4.2 Phospholipids Structure HYDROPHOBICHYDROPHILIC Phospholipids are called amphipathic molecules Hydrogen bonds with water No hydrogen bonds with water

5. The 'head's have large phosphate groups, thus they are hydrophilic (attract water) or polar. The fatty acid tails are non-charged, hydrophobic and repel water. This creates a barrier between the internal and external 'water' environments of the cell. The 'tails' effectively create a barrier to the movement of charged molecules The individual phospholipids are attracted through their charges and this gives some stability. They can however move around in this plane 2.4.2 Phospholipids Structure

6. Cholesterol Phospholipids The stability of the phospholipids can be increased by the presence of cholesterol molecules. The more unsaturated fatty acids in phospholipids, the more fluid the membrane. Fat composition affects flexibility: Membrane must be fluid & flexible An increase in the temperature increases the fluidity of the membrane The Fluid Mosaic Model

7. Membrane proteins: Peripheral proteins loosely bound to surface of membrane Integral proteins penetrate lipid bilayer, usually across whole membrane transmembrane protein Glycoproteins Play a key role in cell-cell recognition The Fluid Mosaic Model

8. Plasma membrane components

9. ProteinFunction Hormone Binding sites A site exposed on the outside of the membrane allows one specific hormone to bind. A signal is then transmitted to the inside of the cell. Example : Insulin receptor Immobilized enzymes Enzymes located in the membrane with the active site on the outside. Example: in the small intestine Cell adhesion To form tight junctions between groups of cells in tissues and organs Cell-to-cell communication For example receptors for neurotransmitters at synapses Channels for passive transport To allow hydrophilic particles across by facilitated diffusion Pumps for active transport Which use ATP to move particles across the membrane 2.4.3 List the function of membrane proteins

10. 2.4.4 Define Diffusion and Osmosis 1.Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration. 2. Osmosis is the diffusion of water molecules, across a partially permeable membrane.

11. 2.4.5 Transport across Membranes inside cell outside cell lipid salt aa H2OH2O sugar NH 3 What molecules can NOT get through directly? ions salts, ammonia large molecules starches, proteins Polar molecules H 2 O can only diffuse at low rates high low Facilitated Diffusion through protein channels channels move specific molecules across cell membrane no energy needed SIMPLE DIFFUSION FACILITATED DIFFUSION

12. Cells may need to move molecules against concentration gradient shape change transports solute from one side of membrane to other protein “pump” “costs” energy = ATP low high ATP 2.4.6 Active transport

13. Getting through cell membrane 1. Passive Transport Simple diffusion diffusion of non-polar, hydrophobic molecules lipids high  low concentration gradient Facilitated diffusion diffusion of polar, hydrophilic molecules through a protein channel high  low concentration gradient 2. Active transport diffusion against concentration gradient low  high uses a protein pump requires ATP

14. Getting through cell membrane

15. Cytoplasm Phagocytosis Food vesicle Golgi apparatus Lysosomes Plasma membrane Digestion of phagocytized food particles or cells Endoplasmic reticulum Extracellular fluid Transport vesicle 2.4.7 Vesicle Transport within the cell

16. 2.4.8 Endocytosis & Exocytosis Moving large molecules into & out of cell through vesicles & vacuoles endocytosis 1. phagocytosis = “cellular eating” 2. pinocytosis = “cellular drinking” 3. receptor mediated endocytosis exocytosis