Cell Membranes
- Created by: Eleanor Izzard
- Created on: 07-12-12 18:54
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- Cell Membranes
- Role of membranes
- holding the components of metabolic pathways in place, regulating the transport of materials into or out of cells
- separating cell contents from the outside environment, separating cell contents from cytoplasm, cell recognition/ signalling,
- Phospholipid Bilayer
- Phosphate head is hydrophillic, lipid tails are hydrophobic. This comes from the way charges are distributed across the molecule
- If phospholipid molecules are mixed with water they form a layer at the surface
- If phospholipid molecules are surrounded with water a bi-layer can form. In this state the molecules can move freely
- rarely some may 'flip flop' from one mono-layer to the other
- the head cannot easily pass through the hydrophobic region of the bi-layer - giving it some stability
- the phospholipid molecules are not bonded together
- Is the basic structure of all biological membranes
- the hydrophobic layer formed creates a barrier to many molecules and separates the cell contents from the outside
- the thin layer of oil is an ideal boundary - where metabolic reactions take place
- 7-10nm thick
- Performing the Functions
- number and type of various components varies according to the function of the particular membrane. This specialisation is part of the differentiation process
- some membranes are up to 1000 times more permeable to water because they contain aquaporins
- all membranes are permeable to water molecules because water molecules can diffuse through the lipid bilayer
- number and type of various components varies according to the function of the particular membrane. This specialisation is part of the differentiation process
- A partially permeable membrane - is permeable to water and some solutes
- Fluid Mosaic Model
- Cholesterol - gives the membranes of some eukaryotic cells mechanical stability. Fits between fatty acid tails and helps make the barrier more complete
- substances like large molecules and ions cannot pass easily and directly through the membrane
- Channel Proteins - allow the movement of some substances across the membrane. Some molecules are too large and too hydrophilic to pass directly through the bilayer
- Carrier Proteins - actively move substances across the membrane
- Receptor Sites - some allow hormones to bind with the cell so that a cell can carry out a cell response
- Glycoproteins /lipids - cell recognition, receptor sites and cell adhesion
- Cholesterol - gives the membranes of some eukaryotic cells mechanical stability. Fits between fatty acid tails and helps make the barrier more complete
- Temperature
- increasing gives molecules more kinetic energy, so they move faster. The increased movement makes membranes leaky, allowing things to leave/enter the cell
- As temperature increases, the proteins in the membrane can become denatured
- Role of membranes
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