Movement Through the Cell Membrane

1. Movement Through the Cell Membrane http://programs.northlandcollege.edu/biology/biology1111/animations/passive1.swf

2. Partially permeable membrane • Generally, small particles can pass through… …but large particles cannot Selectively-Permeable Membranes • A selectively-permeable membrane will allow certain molecules to pass through it, but not others.

3. Structure of the Plasma/Cell Membrane Plasma Membranes consist of 2 types of molecules – phospholipids and proteins

4. Diagram of a Phospholipid Phospholipids have 2 regions: Polar head region: attracts water molecules (hydrophilic) Phosphorous group Non-polar tail region: nonpolar tails repel water molecules (hydrophobic). Made of long carbon chains (fatty acids)

5. Phospholipid bilayer Due to the hydrophobic and hydrophilic nature of the phospholipid, a double layer is formed where the heads protect the tails from the water. This is called the phospholipid bilayer. The bilayer is fluid, not a hard shell.

6. Proteins are Embedded Within the Bilayer Proteins act as passageways for nonpolar (hydrophobic) molecules to pass through. Without proteins embedded in the bilayer, essential molecules needed for communication, energy, etc., would not reach the interior of the cell.

7. Proteins are Embedded Within the Bilayer (continued) The model of the lipid bilayer with embedded proteins is called the Fluid Mosaic Model.

8. TWO Types of Transport Through a Cell Membrane 1. Active Transport – the movement of molecules through a cell membrane using energy 2. Passive Transport – the movement of molecules through a cell membrane without the expenditure of energy

9. 3 Types of Passive Transport Diffusion - Movement of molecules from areas of high concentration to low concentration Osmosis - Diffusion of water molecules from higher concentration of water to lower concentration of water Facilitated Diffusion - Diffusion through pores or channel proteins

10. DIFFUSION Molecules tend to move from areas where there is more of them to where there is less high concentration low concentration This is called moving WITH the concentration gradient. Diffusion continues until equilibrium is reached, or where molecules are equally distributed. Some solutes will be able to move through when others will not.

11. Diffusion (continued) http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html

12. OSMOSIS Water passes through cell membranes rapidly. Osmosis is a specialized form of diffusion that moves water molecules through membranes. Osmotic pressure–when more water molecules accumulate inside a cell, pressure increases. This pressure is called osmotic pressure. when osmotic pressure is high inside the cell, water will want to leave the cell.

13. OSMOSIS

14. 3 Types of Solutions hypertonic solution -solute concentration is HIGHER in the solution than in the cell. Water will move out of the cell- cell will shrivel hypotonic solution - solute concentration is LOWER in the solution than in the cell. Water will move into the cell- cell will swell isotonic solution - EQUAL solute concentrations in the solution and in the cell. Water will move in and out of the cell at equal rates. http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html

15. FACILITATED DIFFUSION some molecules cannot diffuse through on their own (membrane is impermeable to them), and will need assistance (facilitate). Passive transport aided by proteins. Each are very specific to the size/shape/polarity of solute. -transport proteins -channel proteins *aquaporins- facilitated diffusion of water *ion channels- open and close in response to a stimulus (gated channels) http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html

16. Active Transport Some molecules exist in low amounts on one side of a membrane and need to be moved to areas of high amounts active transport- the use of energy to move molecules from LOW concentration to HIGH concentration (against or opposite the concentration gradient) Cell membranes have mechanisms to move these molecules against their concentration gradients: ion/molecular pumps endocytosis exocytosis http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html

17. Types of Active Transport 1. ion/molecular pumps -Molecules can be moved through the membrane by specific proteins embedded in the membrane -Na, K, Ca ions are transported in this manner -sodium-potassium pump is the major pump of animal cells -proton pump is main pump of plants, fungi, and bacteria

18. 2. endocytosis- process of cells engulfing large particles by forming a vesicle around them -different names for different sizes of particles: pinocytosis(cell drinking) -occurs if the particles have been partially broken down into a liquid of tiny dissolved molecules phagocytosis(cell eating) - If the particles are cell fragments or organic matter 3. exocytosis-process by which wastes or secretions (hormones) are brought to the cell membrane, packaged into vesicles and sent out of the cell the reverse of endocytosis