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39 Cards in this Set
- Front
- Back
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Where are plasma membranes found? |
Around cells and organelles |
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What is the plasma membrane made of? |
Proteins and phospholipids arranged in a bilayer |
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How can you see a plasma membrane? |
Using an electro microscope. The bilayer appears as 2 dark bands |
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How large is the membrane? |
The distane across it is 7nm |
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What type of barrier is a phospholipid bilayer? |
A partially permeable barrier |
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What is a partially permeable barrier? |
One which chooses which substnaces can pass through |
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What is a semi-permeable barrier? |
One which allows some substances to pass through |
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What model is used for membranes? |
The fluid mosaic model |
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What is the fluid mosaic model? |
A model of how the components in the membrane are arranged. Molecules aren't bonded together, so there's some movement but it's relatively stable due to the nature of the phospholipid. |
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Who proposed this model and when? |
Singer and Nicholson in 1972 |
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Which part is the fluid? |
The phospholipids and proteins which move around each other |
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Which part is the mosaic? |
The arrangemet of proteins within the phospholipid bilayer. |
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What are the components of a membrane? |
Phospholipids Cholesterol Glycolipids Proteins Glycoproteins |
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What do phospholipids do? |
They make up most of the membrane and are arranged in a bilayer. The hydrophilic head is on the outside and the hydrophobic tail is inside. |
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What does the phospholipid bilayer do? |
It allows lipid soluble molecules to diffuse through however, it acts as a barrier to water soluble (polar) molecules |
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What is cholesterol? |
It is a steroid molecule which fits between fatty acid tails, completing the membrane barrier to water and ions. It's found in eukaryotic cells for stability and fluidity. |
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What does cholesterol do? |
It binds to the hydrophobic tails of the phospholipids, causing them to pack more closely together. It also maintains stability and regulates fluidity. |
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What are glycolipids? |
A phospholipid with a carbohydrate attached |
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What do glycolipids do? |
They act as receptors and do cell signalling and recognition. |
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What types of proteins are there? |
Intrinsic and extrinsic proteins |
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What are instrinsic proteins? |
Channel or carrier proteins which allow the transport of hydrophilic and large molecules through the bilayer. They span the whole membrane. |
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What do channel proteins do? |
They transport substances through diffusion |
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What do carrier proteins do? |
They transport substances through facilitated diffusion |
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What are extrinsic proteins? |
Proteins which span half of the membrane. They act as receptors, transport enzymes and do cell signalling and recognition. |
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What are glycoproteins? |
Proteins with a carbohydrate attached. |
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What do glycoproteins do? |
They act as receptors for signalling molecules They act as antigens for cell recognition. They also bind cells together to the basement membrane,making tissues. This is cell adhesion. They also form H bonds with H20 molecules to stabilise the membrane. |
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What are the roles of the cell membrane within the cell? |
1)Compartmentalisation 2)They hold the components of metabolic pathways in place. 3)The site of attachment for enzymes/ribosomes 4)Controls what enters/leaves organelles |
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What does compartmentalisation mean? |
It separates cell components from cytoplasm |
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What are the roles of the membrane at the surface of cells? |
Cell recognition and signalling Separating cell contents from the outside environment. Regulating transport of materials in and out of cells. |
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How does temperature affect plasma membranes? |
It affects how much the phospholipids in the bilayer can move , which affects membrane structure and permeability. |
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What happens to the membrane below 0 degrees c? |
The phospholipids don't have much kinetic energy, so they can't move very much. They're packed closely together and the membrane is rigid, increasing permeability. Ice crystals may form and pierce the membrane, making it highly permeable when it thaws. |
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What happens to the membrane at temperatures between 0 and 45 degrees c? |
The phospholipids can move around and aren't packed as tightly together-the membrane is partially permeable. As temp increases, the phospholipids move more as they have more kinetic energy, this increases permeability of the membrane |
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What happens to the membrane above 45 degrees c? |
The phospholipid bilayer starts to melt (break down) and becomes more permeable as the membrane disrupts. Water inside the cell expands, putting pressure o the membrane, Channel and carrier proteins denature, so they can't control what enters/leaves the cell. This increases permeability. |
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Why can phospholipids only move in the plane of the bilayer? |
The hydrophilic phosphate head can't pass through the hydrophobic region in the bilayer |
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What types of molecule are likely to be involved in Cellsignalling and recognition ?
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External proteins and glycoproteins |
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If a protein spans the membrane what property must the part of the protein embedded in the central part of the bilayer have?
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It mustbe constructed from amino acids with hydrophobic R groups.
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Explain how phospholipids and proteins influencethe permeability of a cell surface membrane
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The phospholipids allow small and fat soluble molecules through. Carrier and channel proteins allow ions and polar molecules which can't pass through the bilayer through. |
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Botulinum toxin binds to the ends of nerves and prevents them from releasing chemicals that normally cause muscles to contract, There are eight difference botulinum toxins some stronger than others. Suggest why some of the toxin molecules are more potent than others.
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Different toxins will have slightly different shapes, and so will attach more or less strongly to their target membrane proteins.
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What does the proportion of saturated and unsaturated fatty acid tails determine? |
The fluidity of the membrane. The more unsaturated fatty acid tail, the more fluid the membrane. |
