Plasma Membrane or the Plasmalemma. Year 12. Places found :- Around animal cells and plant cells....
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Transcript of Plasma Membrane or the Plasmalemma. Year 12. Places found :- Around animal cells and plant cells....
![Page 1: Plasma Membrane or the Plasmalemma. Year 12. Places found :- Around animal cells and plant cells. Vesicles for transport of substances in / out of cells.](https://reader035.fdocuments.us/reader035/viewer/2022072014/56649e7e5503460f94b80cbc/html5/thumbnails/1.jpg)
Plasma Membraneor the
Plasmalemma.
Year 12
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Places found :-
• Around animal cells and plant cells.
• Vesicles for transport of substances in / out of cells =Endo/Exocytosis.
• Endoplasmic Reticulum (ER)
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Functions
• To control the movement of substances into and out of cells
• To keep the cells contents together and separate from other cells
• To allow communication between cells
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Structure.
• A phospholipid bilayer about 7-10nm thick.
• Under the light microscope it appears as a thin line and until the advent of the electron microscope the structure could not be studied.
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Phospholipids
• A special type of lipid• 2 fatty acid chains
making a hydrophobic tail.
• Chains have no charge and are non-polar / insoluble.
• Phosphate group is hydrophilic = has a charge so is soluble.
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History of Packing :-
1930-40 Danielli and Davson studied triglyceride lipid bi-layers over water surfaces.
Found they arranged themselves with polar heads facing outwards = forming droplets
However, if they add proteins they formed sheets over water as this decreased the surface tension.
NB. The polar pore.
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1950 Robertson Model
• Did not see the spaces for pores on electron micrographs.
• He said that the rail road track was due to the binding of Osmium tetroxide to proteins and polar groups on the surfaces of the membrane.
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• 1966 Lenard and Singer
• Noted over 30% of proteins were twisted into an alpha helix (secondary structure)
• More likely the proteins were spherical than flat.
• Major turning point :- Freeze Fracturing technique
• Clearly showed bumps in membrane as proteins.
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• Proteins are embedded in the bilayer.
• Transmembrane proteins pass through the bilayer
• Others may be inserted at the cytoplasmic or exterior face = Extrinsic / Intrinsic
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Singer and Nicholson 1972
• Aided by electron microscope Singer and Nicholson proposed the fluid mosaic model
• Fluid = moving ; mosaic = made of pieces
• A bilipid layer with proteins + Cholesterol molecules between the phospholipids and polysaccharides attached to the proteins or lipids and constantly moving.
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The Fluid Mosaic Model
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Cholesterol
Cholestrol helps to keep the lipid layer free to move.
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Membrane proteins
• Create pores through which water and water soluble chemicals can pass
• Act as carriers in active transport
• Form receptor sites for hormones
• Are important in cell recognition
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Glycoproteins and Glycolipids.
• All proteins with sugar side chains are involved in cell –cell signalling and self recognition.
• This is important in the immune system response and recognising bacterial invasion