Chapter 5

1. Chapter 5 The Working Cell

2. 5.1 Membrane- Fluid Mosaic • The membrane of cells is composed of two layers • These layers are made of phospholipids • The hydrophobic center is “water hating” while the hydrophilic heads are “water loving”

3. 5.1 Membrane- Fluid Mosaic • This phospholipidbilayeris referred to a fluid mosaic • This is because its remains in fluid-like state where imbedded materials can move freely • Also there is a mosaic of embedded proteins and other materials

4. 5.1 Membrane- Fluid Mosaic • Cholesterol is imbedded in the phospholipidbilayer as well • Cholesterol helps stabilize the membrane at warm temperatures ( from getting too fluid) and keeps the membrane fluid in cooler temperatures

5. 5.1 Membrane- Fluid Mosaic • Six major Functions Performed by Cell Membrane Proteins (pg74) • Attach to the cell membrane and maintain shape/structure • Signal transduction • Enzymatic activity • Cell-cell connectivity • Intercellular joining • Transport

7. 5.1Membrane- Fluid Mosaic • This Bilayer is known to be selectively permeable • Membrane that allows some substances in and prevents others • Being selectively permeable the cell can maintain its internal environment and maintain homeostasis

8. 5.2-Membranes Form Spontaneously • As you should know phospholipids are the key component of the cellular membrane • Turns out this structure actually forms spontaneously and doesn’t require genes nor any other mechanism outside of its own properties Synthetic membrane created in a lab Hydrophobic and hydrophilic portions form together automatically

9. 5.3- Passive Transport • Diffusion- tendency for particles of any kind spread out evenly in the available space • Result because molecules are constantly moving and bumping into each other because of heat energy • If solutions are not in equilibrium (meaning that all the particles are evenly spaced out) they will move to reach equilibrium Molecules continue to move after equilibrium

11. 5.3- Passive Transport • This movement goes down a concentration gradient – Movement from high to low • Diffusion does not require energy • Again, some substances can move through that selectively permeable membrane

12. 5.3- Passive Transport • These processes involving diffusion are referred to collectively as passive transport because they do not require energy • Think about our experiment yesterday • What was happening here? • What moved where? • What could go through the dialysis tubing?

13. 5.4 – Osmosis of water • Osmosis – The diffusion of water across a selectively permeable membrane • Notice how the solute in this image is too large for this membrane • In this solution the movement the water is to the left- see how there are less water molecules available on the left

14. 5.4 – Osmosis of water

15. Do Now • Explain the process of diffusion • Describe how the membrane is a fluid mosaic • Give me three functions of a membrane protein

16. 5.5 Water Balance -Tonicity • Tonicity- ability of a surrounding solution to gain or loose water • This ability to gain or loose water hinges on the concentration levels • Three circumstances: • Isotonic • Hypotonic • Hypertonic

17. 5.5 Water Balance -Tonicity Water In = Water Out • Isotonic (equal)- In a isotonic solution there is no net movement of water and the cells volume remains constant • In animal cells this is the “normal” condition • For plants it is in a limp state. Plant cells need a net inflow of water

18. 5.5 Water Balance -Tonicity Water in > Water out • Hypotonic (below)- situation where the solution has a lower solute concentration than the cell. This causes an influx of water into the cell • In animal cells it causes the cell to expand and potentially burst (lyse) • In plant cells it is actually the preferred situation. Allows plant cells to be turgid- allows structures to be stiff/rigid

19. 5.5 Water Balance -Tonicity Water in < Water out • Hypertonic (above)- situation where the solution has a higher concentration of solute than the cell. Water moves outward • Both plant and animal cells loose water and become shriveled. The term plasmolyzed is used to describe the plant cell

21. 5.5 Water Balance -Tonicity • For plant and animal cells to survive they must regulate there uptake and water loss • This process is called osmoregulation-control of water balance For example typically a fish lives in an hypotonic environment. Its gills and kidneys are used to constantly remove excess water from its body

22. 5.6 Facilitated Diffusion • Nonpolar (hydrophobic ) molecules can cross through the phospholipidbilayer • Polar (charged ) molecules have difficulty moving across this membrane and require a specific protein through a process called facilitated diffusion • Type of passive transport that uses transport proteins to move polar molecules across the membrane (high to low) May act as a simple channel or as a gate, both types are specific to the substance being passed

24. 5.6 Facilitated Diffusion • Water molecules move very slowly across the membrane (polar) they may also use a different pathway to cross the cellular membrane • May use a structure called aquaporinwhich selects only water molecules to pass through the membrane Passive Process

25. 5.7-Discovery of Aquaporins • Dr. Agre discovered the existence of aquaporins by isolating the proteins found on red blood cells (200,000 per cell!) • Our body requires these aquaporins to quickly move large amounts of water in and out of cells Kidney cells filter out many liters of water each day. Without these aquaporins the process would be dangerously slow.

26. Do now • Explain what happens; also determine if its is isotonic, hypotonic, or hypertonic A and • A B 5% Sucrose 25% sucrose 10% sucrose 20% Sucrose

27. 5.8-Active Transport • Active transport- is a mechanism that uses energy to move a solute against its concentration gradient (low to high) • Most methods use ATP as the energy source • Solutes are moved against the concentration gradient through a step by step process

28. 5.8-Active Transport • Shown is the sodium potassium pump • The solute first binds to the protein (Na+) • Then ATP delivers the energy • The protein changes shape and releases the solute on the other side • Potassium reverses this process

30. 5.9- Exocytosis and Endocytosis • Exocytosis-transport process where the cell exports bulky materials (proteins or polysaccharides) Once the vesicle binds to the cell membrane it will spill its contents Notice how it then becomes part of the cell membrane and extends its length

31. 5.9- Exocytosis and Endocytosis • Endocytosis (“inside”)- Transport process that cells use to bring bulk materials in • Three types you should know

32. 5.9- Exocytosis and Endocytosis • Phagocytosis (“Cellular Eating”)- type of endocytosis where the cell engulfs a large particle by wrapping is pseudopodia around the object and taking it inward to form a food vacuole • From here the cell uses lysosomes with hydrolitic enzymes to digest the materials

33. 5.9- Exocytosis and Endocytosis • Pinocytosis (“Cellular Drinking”)- endocytosis where the cell takes in the contents of the liquid portion including solutes • During this process the cell does not select the contents it takes in

34. 5.9- Exocytosis and Endocytosis • Receptor Mediated Endocytosis- endocytosis that is highly selective • The cell membrane is coated with receptor proteins that bind to a particular molecule • Then it is engulfed inward drawing in the molecules

36. Tonicity Review

37. Active and Passive Transport