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Topic 2- Membranes
Triglycerides are a type of lipid. A phosphate group in place of 1 fatty acid chain.
They are made from glycerol and fatty acids. Polar hydrophilic head.
Glycerol- a small 3 carbon molecule with 3 OH groups. 2 non polar fatty acid tails.
Fatty acids- large molecules with a non-polar
hydrocarbon chain (R group) and a polar carboxyl group
(COOH). Phospholipids are the main components of cell membranes.
They form a double phospholipid bilayer with the hydrophilic
1 glycerol molecule joint so 3 fatty acid chains in a
heads facing outwards, making vesicles.
condensation reaction forming an ester bond.
Insoluble in water.
Used for storage, insulation and protection.
Good for energy storage.
Can't be mobilised quickly so are not very useful if
energy is required quickly.
Saturated vs Unsaturated
Saturated if only C-C single bonds.
High melting point.
Fats in warm blooded animals.
Solid at room temperature.
Unsaturated if they contain C=C double bonds.
Polyunsaturated if more than one C=C bond.
Found in cold blooded animals and plants.
Liquid at room temperature.
The Fluid Mosaic Model
Cell membrane surrounds all living cells.
Controls how substances move in and out of
So called because all the components move
around (fluid) and there are many different
components that fit together (mosaic).
o Phospholipid bilayer.
o Carbohydrates- glycoproteins and
Arranged in a bilayer with hydrophilic phosphate heads facing outwards and the tails in the middle.
Forms a thin flexible sheet.
The hydrophobic layer acts as a barrier to most molecules.
Cholesterol links the fatty acids today, strengthening and stabilising the membrane.
Transport proteins- aid the transport of small molecules by facilitated diffusion and active transport.
Receptor proteins- on the outer surface of the membrane and have a specific binding site where hormones can bind in a
hormone-receptor complex. The binding triggers events inside the cell.
Enzymes- catalyse reactions in the cytoplasm or outside the cell e.g. maltase in the small intestine.
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Recognition proteins- glycoproteins that are involved in cell recognition e.g. A and B antigens in blood.
Structural proteins- on the inside surface of the cell and are attached to the cytoskeleton. Involved in maintaining/
changing the cell's shape.
Found on the outer surface of eukaryotic cell membranes.
Attached to membrane proteins or phospholipids.
Movement Across Membranes- Diffusion
Diffusion is the random movement of particles due to thermal motion from a higher concentration to a lower concentration
(down a concentration gradient).…read more
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A solution is hypertonic if it has a lower water potential (more concentrated) than the cell.
A solution is hypotonic if it has a higher water potential (more dilute) than the cell.
Surrounding Solution Hypotonic Surrounding Solution Isotonic Surrounding Solution Hypertonic
Animal Net diffusion of water into cell- No net diffusion, so no change in Net diffusion of water out of cell-
Cell Cell swells and bursts (lysis). cell volume. Cell shrinks and crenates.…read more
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The rate of facilitated diffusion increases as the concentration gradient increases but is limited by the number of carrier
The rate of active transport is constantly high even when there is no concentration gradient across the membrane but it
stops if cellular respiration stops.
Rate of Diffusion = Surface
Area ×Difference in Concentration
T hickness of Exchange Surface
A surface adapted for efficient diffusion will:
Have a surface area as large as possible.
Maintain a large concentration difference.…read more