Cell Organelles. Cell Membrane Controls chemical traffic in and out of the cell Selectively...
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Transcript of Cell Organelles. Cell Membrane Controls chemical traffic in and out of the cell Selectively...
![Page 1: Cell Organelles. Cell Membrane Controls chemical traffic in and out of the cell Selectively Permeable 8 nm thick.](https://reader036.fdocuments.in/reader036/viewer/2022062308/56649cf75503460f949c6a56/html5/thumbnails/1.jpg)
Cell Organelles
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Cell Membrane
• Controls chemical traffic in and out of the cell
• Selectively Permeable
• 8 nm thick
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What is Selective Permeability?
• Allows some substances to cross more easily than others
• Why must it be selective?
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Why Must Cells Allow Some Substances to Pass Across the
Membrane?• To maintain HOMEOSTASIS =
– the tendency to maintain stability in an organism amid environmental change
– (ability to adjust to changes)– ---------------------------------------------------------– *cells must be able to receive info, move water
molecules, food particles, & ions across the membrane
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Membrane Structure• Synthesized in ER
• sugars added in ER & Golgi
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Cell Membrane Synthesis
• AP Bio Book Reference
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Membrane Structure (Con’d)
• Lipid Bilayer (2 layers of phospholipids)
layer #1
layer #2
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The Phospholipid• hydrophilic (water loving) polar heads
•hydrophobic (water fearing) nonpolar tail
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Phospholipid Bilayer
• Polar head - attracted to H2O (hydrophilic)
• Nonpolar tails - push away or repel H2O (hydrophobic)
• -----------------------------------------------------
• In order to best interact w/ H2O inside & outside of cell, membrane forms 2 layers of phospholipids
• hydrophobic interactions hold membrane together
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What is allowed to easily pass through?
• 1) Nonpolar (hydrophobic) molecules dissolve easily in membrane
-hydrocarbons (molecules with C & H)
-oxygen
-(smaller molecules move faster)
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What can easily pass through?
• 2) Polar (hydrophilic) uncharged molecules
- water, carbon dioxide
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What can easily pass through?
• 3) Small, polar molecules- pass easilly between membrane lipids
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What cannot pass through easily?
• Ions & large polar molecules
-do not easily pass thru membrane hydrophobic area
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Fluid Mosaic Model
• 1) Lipid Bilayer -tough but flexible• 2) Transport (channel or carrier) Proteins• 3) Receptor Proteins• 4) Marker Proteins• http://www.virtualcell.com/
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Lipid Bilayer (con’d)
• 1) Stops large polar molecules
-cannot pass thru NONPOLAR tails
-thus, membrane serves as protective BARRIER
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Lipid Bilayer (con’d)
• 2) is FLUID-not rigid
-phospholipid & proteins
can move laterally
(rarely flip)
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Membrane Fluidity
• Dependent on composition
-unsaturated vs. saturated fatty acid tails
-cholesterol
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Transport Proteins
• Look like doughnuts in membrane surface
• allow many impt. molecules & ions to cross
• specific for substances they transport or translocate
• like locked doors - will only let some thru
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Transport (Carrier) Proteins
Can be carrier proteins which do not extend all the way thru the membrane
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How Carrier Proteins Work
Carrier Proteins bond and drag molecule thru bilayer and release on other side
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Transport (Channel) Proteins
Can be channel proteins that span the length of the membrane
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How Channel Proteins Work
Molecules randomly move through by a process called diffusion
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Physical Structure of Transport Proteins
-unilateral: embedded partway thru membrane
-transmembrane: completely span membrane
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Types of Transport Proteins
• 1) uniport: carries single solute
• 2) symport:
-translocates 2 different solutes
-move simultaneously in same direction
• 3) antiport:– exchanges 2 solutes– transports molecules in opposite directions– ex: (Na/K pump)
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Receptor Proteins
• Shaped like boulders in membrane
• convey info to inside of cell (communication)
-hormones
• special shape holds only certain type of molecule
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How Receptor Proteins Work
* when molecule of right shape fits receptor protein, it causes a change at other end of receptor, triggering response in cell
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Receptor Proteins
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Marker Proteins
• Look like trees sticking out of membrane
• Have carbohydrates on surface
• “Name Tags” of cells
• Different for every individual
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Marker Proteins
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Cell-Cell Recognition• Based on recognition of cell surface macromolecules• oligosaccharides are probably important cell
recognition markers - vary!• glycolipids
-sugars covalently linked to lipids• glycoproteins
-sugars covalently linked to proteins
N-linked = asparagine
O-linked = serine, threonine
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How can proteins which can be polar fit into nonpolar region of
membrane?• Proteins made of amino acids
• Of 20 aa, some polar & some nonpolar
• Some aa can attract neighboring aa
folding, twisting
unique function
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Protein Variation
• Allows for channel proteins - embed themselves in membrane
• receptor proteins
• marker proteins
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