Cell Structure and Membrane Control

1. Cell Structure and Membrane Control

2. Why are cells so small? Exchange with environment through cell membrane Rate at which cells exchange materials is proportional to their surface area Cells roughly spherical in shape ? volume of the cell increases faster than the surface area � � p � r3 vs. 4 � p � r2 Surface area: volume ratio of cells decreases as they get larger Folds in plasma membrane increases surface area (e.g., mitochondria)���������

4. Why are cells so small?�multicellular�- Large cube made of smaller cubes Surface area of one cube: 1 cm x 1 cm = 1 cm2 All cubes, total surface area: 6 sides x 216 cubes x 1 cm2 = 1296 cm2 Volume = 6 cm x 6 cm x 6 cm = 216 cm3 Surface:Volume = 1296/216 = 6 /1 = 6 6 cm2 of surface area for each cm3 of volume. Larger cube: more surface area and more volume but less surface area for each cubic centimeter of volume. cube made of many smaller cubes is the same size as the large cube but has the same surface:volume as the small cube. To grow larger, organisms add more cells rather than have larger cells

5. Prokaryotes [bacteria and cyanobacteria (blue-green algae)] smaller and more primitive many have a rigid cell wall a sticky outer coat (capsule) protects - helps �glue� bacteria to surfaces (e.g., rocks in streams) surface projections (pili) to help in attachment lacks nucleus ? DNA is coil into a nucleoid region few organelles and organelles have no membranes able to grow and multiply quickly because of their small surface area:volume ratio

6. All species other than bacteria and cyanobacteria more advanced, larger, and contain a nucleus have membrane bound organelles allow many activities to take place within the same other reactions take place on membrane surfaces

10. Cytoplasm cytosol = fluid --- cytoplasm includes all organelles except nucleus contains a number of membrane bound organelles (perform specialized functions) compartmentalization allows a large number of activities to proceed simultaneously in a very limited space

11. DNA � containing region organizes and parcels out hereditary instructions to new cells nuclear pores - too small for DNA but OK for certain small proteins & RNA nucleolus - RNA and proteins that comprise ribosomes are synthesized

13. General Function: Manufacture

14. General Function: Support, Movements, and Communication between Cells

15. General Function: Storage - Breakdown

17. Chloroplast

18. Boundary between cell�s internal and external environment Strength and shape to cell Concentrates chemical material Regulates traffic by Simple diffusion Facilitated diffusion Active transport Osmosis Endocytosis exocytosis

19. Phospholipid Bilayer

21. Proteins in cell membrane

22. Membrane as a �traffic cop� Membranes selectively permeable barriers Some molecules are able to pass through while others cannot Permeable to: Nonpolar molecules like fats lipids Small polar molecules like water, ethanol, CO2, O2 Impermeable to:������������������������ ions and charged molecules like H+, Na+, K+, Ca2+, HCO3- small polar molecules like glucose Macromolecules How is this controlled?

24. Transport Across Membranes Passive transport simple diffusion, facilitated diffusion, osmosis along a concentration gradient does not require energy use by the cell Active transport against a concentration gradient requires energy Endocytosis Phagocytosis pinocytosis) Exocytosis

25. Simple Diffusion spontaneous - does not require energy. movement of particles from an area of higher concentration to an area of lower concentration. greater the concentration difference, the more rapid the net diffusion. leads to equilibrium - when there is uniform concentration rate affected by: Temperature - rate increases as temperature increases Pressure - rate increases as pressure increases Concentration - rate increases as concentration increases Molecule size - decreases as molecule size increases

27. Facilitated Diffusion Special protein channels help move certain substances across membrane Each protein channel is specific for the molecule it is transporting Spontaneous - does not require energy

28. Osmosis movement of water across selectively permeable membrane Occurs when solute can�t pass through membrane but solvent (water) can Occurs spontaneously and requires no energy Water moves from area of high concentration to low concentration

29. Osmosis and Cell Membrane

30. Osmosis and Cell Membrane Contractile Vacuole Cell Wall [drugs break down cell walls of bacteria] Make �microenvironment� isotonic to cell

31. Paramecium Osmotic Regulation

32. Osmotic Balance in Plant Cells

33. Isotonic �microenvironment�

34. Active Transport Movement against concentration gradient Enables cell to concentrate materials inside that are in low concentration in environment Special proteins in membrane use energy (ATP) to transport these substances into the cell Sometimes �downhill� facilitated transport of one molecule to transport another �uphill� In humans, active transport can account for 30% of your resting energy use Sodium-potassium pump (pumps Na+ out and K+ in) Electrical activity of nerves and muscles Helps osmotic potential of cell

36. Use of vesicles to move large molecules Endocytosis (phagocytosis and pinocytosis) used for moving macromolecules into cell that are too big to normally pass through the cell membrane Small indentation forms at cell membrane, moves inward, and pinches off forming a vesicle Phagocytosis ? particles pinocytosis ? fluid Exocytosis Vesicle moves to cell surface � fuses with cell membrane Contents expelled�