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25 Cards in this Set
- Front
- Back
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The role of phospholipids in the plasma membrane
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Phospholipids form a barrier to dissolved substances Phospholipid molecules have a 'head' and a 'tail' Head = hydrophilic Tail = hydrophobic The molecules automatically arrange themselves into a bilayer |
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The role of cholesterol in the plasma membrane
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Cholesterol gives the membrane stability Cholesterol is a type of lipid It's present in all cell membranes It fits between the phospholipids - they bind to the hydrophobic tails causing them to pack closely together |
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The role of proteins in the plasma membrane
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Proteins control what enters and leaves the cell Some proteins form channels in the membrane Other proteins transport molecules and ions across the membrane by active transport and facilitated diffusion Proteins also act as receptors for molecules in cell signalling |
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The role of glycolipids and glycoproteins in the plasma membrane |
They act as receptors for messenger molecules They stabilise the membrane by forming hydrogen bonds with surrounding water molecules They're also site where drugs, hormones and antibiodies bind They're also antigens - cell surface molecules involved in the immune response |
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Fluid Mosaic Model |
Phospholipids form a continuous double layer The bilayer is fluid - phospholipids are constantly moving Cholesterol molecules are present Protein molecules are scattered through the bilayer Some proteins have a polysaccharide chain attached (glycoproteins) Some lipids have a polysaccharide chain attached (glycolipids) |
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Cell signalling |
How cell communicate with each other |
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How does cell signalling work? |
One cell releases a messenger molecule This molecule travels to another cell This messenger molecule is detected by the cell because it binds to a receptor on its plasma membrane |
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How are membranes affected by temperatures below 0°C? |
The phosphoplipids don't have much energy so they can't move very much They're packed closely together - membrane is rigid Channel proteins and carrier proteins denature which increases the permeability of the membrane |
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How are membranes affected by temperatures between 0 and 45°C? |
The phospholipids can move around and aren't packed as tightly together (partially permeable) As the temperature increases the phospholipids move more - this increase permeability |
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How are membranes affected by temperatures about45°C? |
The phospholipid bilayer starts to melt and the membrane becomes more permeable Water inside the cell expands putting pressure on the membrane Channel proteins and carrier proteins in the membrane denature so tehy can't control what enters or leaves the cell - this increases permeability |
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What factors affect the rate of diffusion? |
The concentration gradient - the higher it is, the faster the rate of diffusion The thickness of the exchange surface - the thinner the exchange surface, the faster the rate of diffusion The surface area - the larger the surface area, the faster the rate of diffusion |
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Hypotonic solution |
Solution with a higher water potential than the cell |
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Isotonic solution |
Solution with the same water potential as the cell |
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Hypertonic solution |
Solution with a lower water potential than the cell |
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What happens to an animal cell when there is a hyptonic solution? |
Net movement of water molecules is into the cell The cell bursts |
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What happens to an animal cell when there is an isotonic solution? |
Water molecules pass into and out of the cell in equal amounts The cell stays the same |
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What happens to an animal cell when there is a hypertonic solution? |
Net movement of water molecules is out of the cell The cell shrinks |
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What happens to a plant cell when there is a hypotonic solution? |
Net movement of water is into cell The vacuole swells The vacuole and cytoplasm push against the cell wall The cell becomes turgid (swollen) |
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What happens to a plant cell when there is an isotonic solution? |
Water molecules move into and out of the cell in equal amounts The cell stays the same |
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What happens to a plant cell when there is a hypertonic solution? |
Net movement of water is out of the cell The cell becomes flaccid (limp) The cytoplasm and the membrane pull away from the cell wall This is called plasmolysis |
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Carrier proteins |
They move large molecules into or out of the cell down their concentration gradient A large molecule attaches to a carrier protein Then the protein changes shape This releases the molecule on the opposite side of the membrane |
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Channel proteins |
They form pores in the membrane for charged particles to diffuse through Different channel proteins facilitate the diffusion of different charged particles |
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Active transport |
This is the movement of substances against a concentration gradient A molecule attaches to the carrier protein, the protein changes shape and this moves the molecule across the membrane, releasing it on the other side Energy is used to move the solute against the concentration gradient |
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Endocytosis |
A cell surrounds a large substance with a section of its plasma membrane The membrane pinches off to form a vesicle inside the cell containing the ingested substance |
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Exocytosis |
Vesicles containing large substances (produced by the cell) pinch off from sacs of the golgi apparatus and towards the plasma membrane The vesicles fuse with the plasma membrane and release their contents outside the cell |
