Movement Across the Plasma Membrane The cell membrane is semi-permeable A few molecules move freely Water, Carbon dioxide, Ammonia, Oxygen Carrier proteins transport other molecules Proteins embedded in lipid bilayer Fluid mosaic model – describes fluid nature of a lipid bilayer with proteins

Three Transport types: (don’t write this down) 1. Passive Transport 2. Active Transport 3. Membrane-assisted Transport Endocytosis (phagocytosis & pinocytosis) Exocytosis

1. Passive Transport No energy required Move due to gradient differences in concentration, pressure, charge Move to equalize gradient High moves toward low

Types of Passive Transport a) Diffusion b) Osmosis c) Facilitated diffusion

a) Diffusion Molecules move to equalize concentration

Rate of diffusion - how fast diffusion occurs Factors that affect the rate of diffusion are Molecule size - bigger are slower Molecule polarity - more polar are slower Ion charge - more charged are slower

d) Temperature - directly proportional e) Pressure

b) Osmosis Diffusion of water Into cell Out of cell

Solution Differences & Cells solvent + solute = solution

Solutions can be: i. Hypotonic solution More solutes in cell than outside Outside solvent will flow into cell

Draw it!

ii. Hypertonic solution More solutes outside than inside cell Fluid will flow out of cell

Draw it!

iii. Isotonic solution Solutes equal inside & out of cell

Draw it!

c) Facilitated Diffusion Membranes are differentially permeable Still passive transport: why???

i. Specific channel proteins help molecule or ions enter or leave the cell Hollow tubes Ex. aquaporins

ii. Specific carrier proteins transport molecules across the cell membrane Slower than channels (lower rate of diffusion) Ex. Cytochromes: involved in ATP production

Process of Facilitated Transport 1. Protein binds with molecule 2. Shape of protein changes 3. Molecule moves across membrane

2. Active Transport Primary Active Transport against concentration gradient! Requires energy (ATP) Ex. sodium-potassium pump

If the primary active transport involves ions it creates an electrochemical gradient Combination of a concentration gradient and charge Stores potential energy

b) Secondary Active Transport Uses the electrochemical gradient as a source of energy Used in uptake of amino acids and sugars Ex. Hydrogen-sucrose pump

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3. Membrane-assisted transport

trans-face cis-face

a) Endocytosis Movement of large material Movement is into cell Particles Organisms Large molecules Movement is into cell Types of endocytosis bulk-phase (nonspecific) receptor-mediated (specific)

Process of Endocytosis 1. Plasma membrane surrounds material 2. Edges of membrane meet 3. Membranes fuse to form vesicle

Forms of Endocytosis i) Phagocytosis – cell eating ii) Pinocytosis – cell drinking

b) Exocytosis Reverse of endocytosis Cell discharges material

Steps 1. Vesicle moves to cell surface 2. Membrane of vesicle fuses 3. Materials expelled

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End Chapter 2