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Why are membranes important?
- They are involved in intracellular and intercellular transport
- Membranes allow the contents of eukaryotic cells to be divided into specialed compartments
- They are often the site of complex chemical rections
Membranes are predominantly composed of which two molecules?
Proteins and phospholipids
What is meant by the 'fluid mosaic' model?
A mosaic of proteins bobbing in a fluid bilayer of phospholipids
Which molecule is responsible for the bilayer structure of the membrane and what properties of the molecule enable this to occur?
Phospholipids - they have hydrophillic and hydrophobic sections so the hydrophillic heads form a stable membrane structure in contact with aqueous solutions and the hydrophobic tails stay in the centre of the bilayer away from water
What interactions hold the molecules in the phospholipid bilayer together?
Van der waals forces
What is the role of cholesterol in the plasma membrane?
It alters the fluidity of the membrane by breaking up the van der waals forces and close packing of the phospholipid tails and prevents lipid crystalisation at low temperatures
Cholesterol keeps the plasma membrane _______ fluid at warm temperatures and _______ fluid at low temperatures?
When proteins are embedded in the membrane by strong hydrophobic interactions and cannot easily be washed off by ionic solutions what word is used to describe them?
What are transmembrane proteins?
Proteins that can be embedded in one side only or go across the membrane
When proteins are on the surface of the membrane and can be easily washed off by ionic solutions what word is used to describe them?
What is the name of proteins which are a combination of protein and carbohydrate, are found at the surface of the cell and are involved in cell to cell recognition?
What is the function of passive transport proteins? Give an example of a passive transport protein
- They transport molecules across a membrane down a concentration gradient
- Channel proteins facilitate diffusion
What is the function of active transport proteins?
They pump ions and molecules against a concentration gradient
What provides the energy for the phosphorylation and conformational change of protein pumps?
The hydrolysis of ATP
What is the function of enzymes?
They allow the location of catalysis to be controlled within a cell
What is the function of structural support proteins?
They allow the cytoskeleton to adhere to the membrane for the structural support of the cell. They are also used to attach to the extra cellular matrix to hold the cell in one place
What is the function of cell recognition proteins?
They enable an organism to identify which cells are its own and which cell are not supposed to be present allowing an immune response
What is the function of receptor proteins?
They react to the attachment of hydrophilic signalling molecules stimulating a response within the cell such as the phosphorylation of an enzyme which will then be activated
Why is the plasma membrane likely to be folded in prokaryotes?
To increase the surface area for chemical reactions
Eukaryotes have an endomembrane system - name three organelles that are part of this
- endoplasmic reticulum
- golgi apparatus
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