Cell Membranes
- Created by: Nicola Carter
- Created on: 10-12-12 20:03
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- Cell Membranes
- Roles of membranes
- Separating cell contents from the outside environment
- Separating cell components from cytoplasm
- Cell recognition and signalling
- Holding the components of some metabolic pathways in place
- Regulating the transport of materials into or out of cells
- Phosphlipid bilayer
- Phosphate 'head'
- Hydrophilic -water loving
- Phosphate head stick into the water
- Fatty acid (lipid) 'tail'
- Hydrophobic - water hating
- If phosholipid molecules are completely surrounded by water, a bilayer can form.
- Phosphate heads on each side of the bilayer stick into the water, while the hydrophobic fatty acid tails point towards each other
- Means that the hydrophobic tails are away from water
- Phospholipid molecules can move freely - just like fluid molecules do.
- Gives the bilayer stability
- Phosphate heads on each side of the bilayer stick into the water, while the hydrophobic fatty acid tails point towards each other
- Basic structural component of all biological membranes
- Hydrophobic layer formed by the phosphlipid tails creates a barrier to many molecules and separates the cell contents from the outside world.
- Differentiation of membranes
- Phosphlipid bilayer would be to fragile to function as a barrier without other components
- Examples
- Plasma membranes of the cells in a growing shoot contain receptors the molecules that regulate growth
- Muscle cell membranes contain a large number of channels that allow rapid uptake of glucose
- Phosphate 'head'
- The fluid mosaic model
- Used to describe the molecular arrangemnts in membranes.
- Feature: a bilayer of phospholipid molecules forming the basic structure
- Feature: various protein molecules floating in the phospholipid bilayer, some completly freely, some bound to other components or to sturctures within the cell
- Feature: some proteins partially embedded in the bilayer on the inside or the outside face;other protiens completely spanning the bilayer
- Glycoproteins and glycolipids
- Where phosphlipid molecules have a carbohydrate part attached they are called glycolipids
- Where protein molecules have a carbohdrate part attached they are called glycoproteins
- Membrane components and their roles
- Membranes stability and fluidity
- Cholesterol gives the membranes some mechanical stability. Fits between the lipid tails and makes the barrier more complete
- Membrane transport functions
- Channel proteins allow the movement of large/charged substances across the membrane.
- Carrier proteins actively move large/charged substances across the membrane
- Recognition and communication
- Receptor sites - some allow hormones to bind with the cell so that a cell 'response' can be carried out. A cell can respond to a hormone only if it has a receptorfor that hormone on its cell surface membrane
- Glycoproteins/lipids are involved in cell signalling that they are 'self' to allow recognition to by the immune system
- Membranes stability and fluidity
- Temperature
- Increasing temperature gives molecules more kinetic energy - they will move faster.
- Increased movement of phospholipids and other components makes membranes leaky
- Allows subsutances that would normally not do so to enter or leave the cell.
- Increased movement of phospholipids and other components makes membranes leaky
- Organisms that live in very hot or very cold environments need differntly adapted molecular components of their membranes so that their membranes can perform the functions needed to maintain life
- Increasing temperature gives molecules more kinetic energy - they will move faster.
- Roles of membranes
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