Cell Membrane and Transport Mechanisms

1. Cell Membrane and Transport Mechanisms

2. Cell Membrane • Fluid Mosaic Model - proteins embedded in a phospholipid bilayer.

3. Fluid mosaic model FLUID- because individual phospholipids and proteins can move around freely within the layer, like it’s a liquid. MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above. AS Biology. Foundation. Cell membranes and Transport

4. Cell Membrane • Phospholipid: 1 head and 2 tails • Polar head attract water - hydrophilic • Non-polar tails repel water -hydrophobic

5. Cell Membrane • Bilayer: 2 layers of phospholipids • The polar heads stay on the outside and the tails stay on the inside.

6. Cell Membrane • Cell surface proteins • a. Channel proteins - transport food and other molecules into the cell and transport wastes out of the cells. • b. Receptor proteins - gather information about the cell’s surroundings. • c. Cell surface markers - identify the type of cell, important for cell recognition.

7. Cell Membrane • Permeability of the cell membrane • 1. Semi permeable/selectively permeable - only certain substances can pass across the membrane. • 2. Factors that determine whether a molecule can pass through a membrane or not: • a. size • b. type (polar, non-polar)

8. Transport Mechanisms • Transport Mechanisms - moving material in and out of the cell • Concentration gradient - the difference in the amount of a substance inside and outside of the cell • 1. Going “with the gradient”-moving from high to low concentration • 2. Going “against the gradient”-moving from low to high concentration • 3. Equilibrium exists when the concentration of molecules is the same throughout a space (inside and outside the cell)

9. Transport Mechanisms • Two categories of transport based on concentration gradient and the need for energy • 1. Passive transport that does not require energy, goes with the gradient. • Example = diffusion and osmosis • 2. Active transport requires energy, goes against the gradient.

10. Passive Transport Mechanisms • Diffusion - movement from an area of high concentration to an area of low concentration • Example: smoke across a room, food coloring dropped into water, oxygen in lungs

11. Passive Transport Mechanisms • Diffusion -

12. Passive Transport Mechanisms • Osmosis - diffusion of water • Direction of osmosis-the direction of water flow depends upon the concentration of solute and solvent (water) • Tonicity-term used to compare 2 solutions (usually the inside and the outside of the cell) • a. Hypotonic - less solute (more water) • b. Hypertonic - more solute (less water) • c. Isotonic - equal amounts of solute and water

13. Passive Transport Mechanisms • Osmosis - diffusion of water • Water will flow from a hypotonic solution to a hypertonic solution • Will water move in an isotonic solution? Yes, but it won’t be noticeable-equilibrium is established

14. Passive Transport Mechanisms • Osmosis - diffusion of water • Turgor pressure/osmotic pressure-pressure due to water in cell. • Analogy: air pressure in a tire. • When a cell has high turgor pressure, it is bigger and stiffer. When a cell has low turgor pressure, it is smaller and flimsy.

15. Passive Transport Mechanisms • Click to: See osmosis in action

16. Passive Transport Mechanisms • Plasmolysis - wilting of a cell due to loss of turgor pressure • Cytolysis - bursting of a cell due to an increase in turgor pressure. • How do plant cells avoid cytolysis? Cell walls • How do unicellular freshwater organisms avoid bursting? Contractile vacuoles.

17. Passive Transport Mechanisms

18. Passive Transport Mechanisms

19. Passive Transport Mechanisms • Facilitated diffusion - transport of specific molecules across a membrane with the help of a channel protein • An example of a molecule that is often transported in this manner is glucose

20. Passive Transport Mechanisms • Click to: see facilitated diffusion

21. Passive Transport Mechanisms • Click below to:Go to the passive transport animation!!!

22. Active Transport Mechanism • Active Transport Mechanism(requires energy in the form of ATP) • Sodium-potassium pump - pumps sodium ions out and forces potassium ions in. Important for conducting nerve impulses and muscle contraction.

23. Active Transport Mechanism • Sodium-potassium pump - 1. 4. 3. 2.

24. Active Transport Mechanism • Click to: Check out the animation of the Sodium – Potassium Pump

25. Active Transport Mechanism • Proton pump-transport protons through membranes of chloroplasts and mitochondria

26. Active Transport Mechanism • Endocytosis - process of bringing larger molecules into the cell by engulfing them. • 1. Pinocytosis – liquids • 2. Phagocytosis - solids (amoebas eat this way, white blood cell engulf bacteria

27. Active Transport Mechanism • Click to: see phagocytosis

28. Active Transport Mechanism • Excocytosis - discharge of wastes, hormones or other larger molecules out of the cell (opposite of endocytosis)

29. Active Transport Mechanism • Click to: see exocytosis

30. How Cells Communicate • Organ system involved in communication • 1. Endocrine system - releases hormones (protein) for communication • 2. Nervous system - releases neurotransmitters to other nerve cells or to muscle cells.

31. How Cells Communicate • Receptors • 1. Receptors - are proteins that are or the cell membrane surface - they send messages to the inside of the cell when they encounter certain molecules outside of the cell. • 2. Chemically gated channels - a chemical trigger transmits information. • 3. Voltage gated channel - an electrical signal transmits information along nerve cells.

32. Active Transport Mechanisms • Click below to:Go to the active transport animation!!!