Cell Membrane Structure
- Created by: jessicawarren
- Created on: 11-04-16 11:47
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- Cell Membrane Structure
- Basics
- All cells surrounded by membranes
- In eukaryotic cells, all organelles surrounded
- Barrier between cell and environment. Controls what enters/leaves cell
- Partially permeable
- Substances move across CSM by diffusion, osmosis or active transport
- Fluid Mosaic Structure
- 1972- suggested to describe arrangement of molecules in membrane
- Phospholipids form bilayer
- 'Fluid' because lipids constantly moving
- Cholesterol molecules present in bilayer
- Channel/carrier proteins scattered through bilayer like mosaic- allow large molecules/ions to pass through membrane. Receptor proteins allow detection of chemicals.
- Proteins able to move side ways thorough bilayer, some fixed in position
- Contains glycoproteins/glycolipids- proteins and lipids w/ polysaccharide chain attached
- Components
- Phospholipids: hydrophilic head, hydrophobic tail. Heads face out towards water. Centre hydrophobic- doesn't allow water soluble substances through
- Cholesterol: Molecules fit between phospholipids. Bind to tails causing them to pack closely together- restricts movement , membrane less fluid, more rigid. Maintain shape of animal cells
- Permeability practical
- 1: Using a scalpel, cut 5 equal sized pieces of beetroot. Rinse to remove pigment.
- 2: Add pieces to different test tubes containing 5cm3 water (measured w/ pipette)
- 3: Place each test tube in water bath at different temp e.g. 10,20,30,40,50 degrees for same length of time
- 4: Remove beetroot from liquid
- 5: Using a colorimeter, measure absorbance. Higher = more permeable
- Increasing Temp
- Below 0- phospholipids have low energy, packed closely together, rigid membrane. Channel/carrier proteins deform, increasing permeability. Ice crystals may form and pierce membrane, highly permeable when it thaws
- 0-45: phospholipids can move, not as closely packed, partially permeable membrane. As temp increases phospholipids move more, increasing permeability of membrane
- Above 45: bilayer starts to melt, increases permeability. Water in cell expands, pressure on membrane. Channel/carrier proteins deform, more permeable membrane
- Basics
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