Membrane

1. Membrane

2. Cells require a coat to ensure that their internal environment remains constant. • The same applies for organelles. • Characteristics of membrane: a. Membranes are not static and rigid b. Complex and dynamic c. Comprises of proteins and lipids (proteins constitute 20 to 80% of total membrane weight) • The content of the membrane influences the function.

3. Membrans are asymmetrical • Membrane structure was elucidated by Singer dan Nicholson pada 1972 • Fluid Mosaic Model

4. Fluid Mosaic Model • Comprises of 2 layers of lipids; mainly phospholipids Membrane bilayer is stabilised by hydrophobic and Van der Waals interactions

5. The surface of membranes are polar and can comprise of functional groups that are charged Ganglioside: sialic acid (glikosphingolipid that are negatively charged at pH 7 Sphingomyelin: (+/-) Cerebroside: (polar)

6. Phosphoacylglycerol: (+/-) Cholesterol

8. 1 2 3 4 5 6 7 8 11 13 15 9 18 17 10 12 14 16 Membrane fluidity depends on lipid content Many saturated fats:Linear arrangement of the hydrocarbon chains cause the the membrane arrangement ot be compact making the membrane rigid Many unsaturated fatty acids:Hydrocarbon chains are bent causing their arrangement to be unorganised: making membrane fluid.

9. Cholesterol (rings are rigid):Membrane arrangement more systematic and rigid: rigid and hydrophobic cholesterol ring increases van der Waals interactions

10. Distribution and type of fatty acid differs between the inner & outer membrane Molecules are bigger Molecule arrangement more compact

11. Proteins in Membranes • Core of the membrane contains proteins that are associated with the membraneThe proteins vary in size, content and shape 2 types of proteins: a. peripheral protein b. integral protein

12. A major portion is embedded in the membrane Can be removed by mild chemical treatment I I I P P Transverses Membranes

13. Usually -heliks or -pleated sheet

14. I I I P P P

15. Transport proteins To carry materials across membranes Identification Role of Proteins in Membrane Metabolism Receptor Proteins (receives signals)

16. Why is the membrane asymetrical?

17. Transport in membranes • Only certain molecules can cross the membrane • Membranes are permeable if it allows substances to cross it • Membranes are impermeable if it does not allow substances to cross it

19. Membrane transport Small molecules Passive Transport Active Transport Pump Carrier Diffusion Facilitated Diffusion Water Channel Non polar Carrier ions Large Molecules Endositosis Eksositosis Pinositosis

21. Diffusion (Passive Transport) • Movement of molecules follow a concentration gradient: from high to low concentration • Does not require energy • Movement of small uncharged molecules: CO2, O2, N2, H2O • Diffusion stops when the concentration on both sides are balanced

22. Osmosis • Diffusion (movement) of water across a semi permeable membrane: also an example of diffusion • Water moves from a section which has a high water concentration to one with a low water concentration ( i.e from a dilute solution to a concentrated solution)

23. Hypertonic Solution: Surrounding fluid has a high solute concentration than inside the cell (ie the concentration of water outside the cell is low) Hypotonic Solution: Surrounding fluid has a lower solute concentration than inside the cell (ie the concentration of water outside the cell is high)

24. B A B A A B

25. Transport using a carrier • Facilitated diffusion Involves a concentraion gradient Movement form high to low concentraion Substances will enter the cell by binding to a protein Protein changes shape and carries the substance into and out of the cell Eg: sugar and amino acid Movement via a Protein Carrier Movement via a channel Protein hydrophobic on the outside but hydrophyllic on the inside Note that glucose changes to form glucose-phosphate so that it cannot exit the cell

27. Active Transport • Movement across a concentration gradient • Requires energy • Eg: Na+ - K+ Pump

28. Perhatikan perubahan konformasi protein

29. Exocytosis • Removal of substances eg proteins, waste outside the cell • Involves fusion of cell membrane Fusion of Membrane

30. Endocytosis Phagocytosis: Intake of substances into cell

31. Pinocytosis • Intake of dissolved materials