Cell Membrane
- Created by: N1ntendo-Sw1tch
- Created on: 25-02-23 17:55
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- Cell Membrane
- structure
- double membrane
- phospholipid bilayer
- barrier is 7-8nm across
- made of phospholipids, proteins and other macromolecules
- Diagram
- function
- protects living cell from non-living surrounding
- takes up nutrients
- secretes chemicals
- allows cell recognition
- selectively permeable to water and some solutes
- why a phospholipid bilayer?
- hydrophilic heads of phospholipids
- hydrophobic tails of phospholipids
- tails = inside heads = outside
- Fluid because the phospholipid molecules are free to move within their layer
- Mosaic because the proteins embedded in the layer are different shapes and sizes
- Membrane proteins
- extrinsic
- occur only on the surface/ partly embedded
- polar/charged and associate with polar phosphate heads
- provide structural support, recognition sites for hormones and cell surface markers (antigens)
- intrinsic
- penetrate lipid bilayer, normally through whole membrane
- transport proteins
- channel proteins and carrier proteins
- extrinsic
- Membrane Permeability
- lipid soluble, gasses, hydrophobic molecules and small polar molecules
- Dissolve in the phospholipids and diffuse across the membrane
- vitamin A, oxygen, carbon dioxide, ethanol, water ect...
- water soluble
- pass through intrinsic proteins (hydrophilic lining) as they cannot diffuse through phospholipids
- glucose, ions, amino acids ect..
- lipid soluble, gasses, hydrophobic molecules and small polar molecules
- factors affecting permeability
- temperature: at low temps the molecules have low KE making the membrane rigid. when temperature is higher the membrane is more fluid so gaps between lipids are larger allowing more through
- but when temperature is too high the proteins denature leaving huge gaps in the membrane and controll of what comes in and out is lost
- Ethanol: ethanol will dissolve the lipids making the membrane porous allowing things to leak out. if there's enough ethanol the membrane will dissintagrate completely. acid can also do this
- detergent: reduces surface tension and disperses the phospholipids in membrane, increasing permeability
- NaCl: sodium ions will bond to phospholipids oxygen in the heads reducing their movement
- temperature: at low temps the molecules have low KE making the membrane rigid. when temperature is higher the membrane is more fluid so gaps between lipids are larger allowing more through
- structure
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