cell membrane & cellular transport homeostasis – the maintenance of internal stable conditions...
TRANSCRIPT
Cell Membrane& Cellular Transport
Homeostasis –the maintenance of internal stable conditionsThe cell membrane keeps the cell in balance.
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.
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
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
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
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
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
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
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.
Endocytosis
PINOCYTOSISPHAGOCYTOSIS
Exocytosis
Transport Summarysimplediffusion
facilitateddiffusion
activetransport
ATP
(Smaller molecules)
(Larger molecules)
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
Osmosis movement of water across cell membrane.
HIGH H2O
LOW H2O
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.
http://www.glencoe.com/sites/common_assets/science/virtual_labs/LS03/LS03.html