movement across the plasma membrane the cell membrane is semi-permeable a few molecules move freely...
TRANSCRIPT
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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
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Three Transport types:(don’t write this down)
1. Passive Transport
2. Active Transport
3. Membrane-assisted Transport– Endocytosis
(phagocytosis & pinocytosis)
– Exocytosis
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1. Passive Transport
• No energy required
• Move due to gradient– differences in concentration, pressure, charge
• Move to equalize gradient– High moves toward low
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Types of Passive Transport
a) Diffusion
b) Osmosis
c) Facilitated diffusion
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a) Diffusion
• Molecules move to equalize concentration
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Rate of diffusion- how fast diffusion occurs
Factors that affect the rate of diffusion are
a) Molecule size - bigger are slower
b) Molecule polarity - more polar are slower
c) Ion charge- more charged are slower
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d) Temperature- directly proportional
e) Pressure- directly proportional
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b) Osmosis
• Diffusion of water
– Into cell– Out of cell
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Solution Differences & Cells
solvent + solute = solution
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Solutions can be:
i. Hypotonic solution– More solutes in cell than outside– Outside solvent will flow into cell
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• Draw it!
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ii. Hypertonic solution– More solutes outside than inside cell– Fluid will flow out of cell
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• Draw it!
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iii. Isotonic solution– Solutes equal inside & out of cell
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• Draw it!
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c) Facilitated Diffusion
• Membranes are differentially permeable
• Still passive transport: why???
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i. Specific channel proteins help molecule or ions enter or leave the cell– Hollow tubes– Ex. aquaporins
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ii. Specific carrier proteins transport molecules across the cell membrane– Slower than channels (lower rate of diffusion)– Ex. Cytochromes: involved in ATP production
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Process of Facilitated Transport
1. Protein binds with molecule
2. Shape of protein changes
3. Molecule moves across membrane
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2. Active Transport
a) Primary Active Transport• against concentration gradient!• Requires energy (ATP)• Ex. sodium-potassium pump
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• If the primary active transport involves ions it creates an electrochemical gradient– Combination of a concentration gradient and
charge– Stores potential energy
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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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• http://bcs.whfreeman.com/thelifewire8e/content/cat_040/0504002.html
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3. Membrane-assisted transport
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cis-face
trans-face
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a) Endocytosis
• Movement of large material– Particles– Organisms – Large molecules
• Movement is into cell
• Types of endocytosis– bulk-phase (nonspecific)– receptor-mediated (specific)
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Process of Endocytosis
1. Plasma membrane surrounds material
2. Edges of membrane meet
3. Membranes fuse to form vesicle
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Forms of Endocytosis
i) Phagocytosis – cell eating
ii) Pinocytosis – cell drinking
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b) Exocytosis
• Reverse of endocytosis
• Cell discharges material
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Steps
1. Vesicle moves to cell surface
2. Membrane of vesicle fuses
3. Materials expelled
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• http://bcs.whfreeman.com/thelifewire8e/content/cat_040/0504003.html
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End Chapter 2