Cell Membrane & Cellular Transport Homeostasis – the maintenance of internal stable conditions The...
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Cell Membrane& Cellular Transport
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Homeostasis –the maintenance of internal stable conditionsThe cell membrane keeps the cell in balance.
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Membrane Functions• Provides a selectively permeable barrier
around the cell. • Controls the passage of substances in and out
of the cell.• Maintains homeostasis for the cell.
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Membrane Structure• Phospholipid bilayer
(nonpolar)• Membrane proteins:
act as transport channels.
• Carbohydrate chains: act as “ID” tags for the cell.
• Cholesterol: provides stability for the membrane.
http://library.thinkquest.org/C004535/media/cell_membrane.gif
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Phospholipid Bilayer– Phospholipids: phosphate head and lipid tail.– Phospholipid Bilayer: two layers.
inside cell
outside cellLipid Tails
Hydrophobic = repels water
Hydrophilic = attracts water
PhosphateHead
Phospholipid Bilayer
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The cell membrane is semipermeable, which means only some material can
get in or out.
AminoAcids H2OSugar Lipids Salt Waste
So what needs to get across the membrane?
O2
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How do you build a semi-permeable cell membrane?
• Channels are made of proteins.• Proteins act as doors in the membrane.
BilipidMembrane
Protein Channelsin Bilipid Membrane
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Diffusion Molecules move from HIGH to LOW concentration; this continues until equilibrium is reached.
• Simple diffusion: directly through membrane.• Facilitated diffusion: help through a protein channel.
NO energy needed!!
HIGH
LOW
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Active Transport• Cells use energy to move against
concentration gradient - from LOW to HIGH.• Particles that are polar (charged) must move
through a protein channel.– Use protein pump– requires energy (ATP)
ATP
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Transport of Molecules• Endocytosis: takes material into cell by cell
membrane making pockets.– Phagocytosis – “cell eating”; cell engulfs particles– Pinocytosis – cell takes in liquid from surrounding
environment.• Exocytosis: process forcing contents out of the
cell.
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Endocytosis
PINOCYTOSISPHAGOCYTOSIS
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Exocytosis
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Transport Summarysimplediffusion
facilitateddiffusion
activetransport
ATP
(Smaller molecules)
(Larger molecules)
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Types of Cellular TransportPASSIVE• Does NOT require
energy• Goes with the
concentration gradient (high to low)
• Simple Diffusion, Facilitated Diffusion
ACTIVE• Requires energy from ATP• Goes against the
concentration gradient (low to high)
• Active Transport, Endocytosis, Exocytosis
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Osmosis movement of water across cell membrane.
HIGH H2O
LOW H2O
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Effects of Osmosis on Cells (osmotic pressure)
• Hypertonic: higher concentrations of solute; less H2O.• Isotonic: equal concentrations of solute.• Hypotonic: lower concentrations of solute; more H2O.
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http://www.glencoe.com/sites/common_assets/science/virtual_labs/LS03/LS03.html