Biological Membranes
- Created by: aidanchester
- Created on: 05-02-18 12:23
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- Fluid Mosaic Model of the Plasma Membrane
- Biological Membranes
- Factors Affecting Membrane Structure and Permeability
- Proteins and lipids are both affected by temperature
- As temperature increases, the membrane becomes more fluid
- Reducing the effectiveness of the barrier
- Reversible change
- Proteins denature at 40 degrees and disrupt the structure of the membrane
- No longer an effective barrier
- Irreversible change
- Increased temperature
- Increased speed of diffusion
- Organic solvents dissolve lipids
- Disrupting structure
- Increasing permeability
- Disrupting structure
- Cell Signalling
- Glycoproteins in the plasma membrane form receptors
- Each receptor is specific to a particular messenger
- Complementary
- A cell that responds to a particular messenger is a target cell
- How do receptors change cells?
- Change in receptor may cause release of a messenger inside the cell
- Change in receptor may result in a protein channel opening
- Change may activate an enzyme within the cell
- Transport of Substances
- Diffusion
- Net movement of atoms/molecules from an area of high conc to low
- Passive process, no energy required
- Facilitated Diffusion
- Ions/small polar molecules
- Larger molecules
- Carrier proteins
- Change shape transferring molecule to the other side
- Carrier proteins
- Passive process
- Active Transport
- Particles cannot pass passively up a concentration gradient
- The cell has to provide energy to move them
- Carrier Proteins
- ATP provides the energy
- Osmosis
- Diffusion of water mlecules
- 'Water potential'
- Animal Cells
- Water potential higher than in the cell
- Water moves into cell and cell bursts
- Water potential lower than in the cell
- Water moves out of the cell
- Cell shrivels and becomes crenated
- Water moves out of the cell
- Water potential higher than in the cell
- Plant Cells
- Water potential higher than in the cell
- Water moves into the cell and becomes turgid
- Water potential lower than in the cell
- Water moves out of the cell
- Cell becomes plasmolysed
- Water moves out of the cell
- Water potential higher than in the cell
- Diffusion
- Endocytosis
- Process by which cells absorb molecules by engulfing them
- Phagocytosis and Pinocytosis
- Pinocytosis
- Small particles and fluid are taken in
- The plasma membrane invaginates inwards
- Membranes fuse around the molecule forming a small vesicle
- Phagocytosis
- Protrusions called pseudopodia
- Larger particles
- Pseudopodia extend from the cell and wrap themselves around particles
- Membrane fuses to seal the particle into a vesicle
- Factors Affecting Membrane Structure and Permeability
- Phospholipid Bilayer
- Phospholipids naturally form a bilayer when they are in contact with water
- Phospholipids have hydrophilic polar heads
- Hydrophilic - Attraction to water
- Phospholipids have hydrophobic non-polar tails
- Hydrophobic - Repulsion from water
- Most stable structure to adopt
- Heads are attracted to water and the tails are repelled
- So the heads are in the aqueous medium and the tails are far from it
- The hydrophobic tails also attract each other
- Further stabilising the structure
- Heads are attracted to water and the tails are repelled
- Channel and Carrier Proteins
- Trans-membrane Proteins
- Function is to transport water-soluble charged particles through the membrane
- As some substances can't get through the lipid bilayer
- Function is to transport water-soluble charged particles through the membrane
- Channel Proteins
- Form a passageway
- Water and polar substances can pass through
- By diffusion down concentration gradient
- Form a passageway
- Carrier Proteins
- Change shape
- Moves substances from one side to the other
- Down a concentration gradient
- By facilitated diffusion
- By active transport
- Change shape
- Trans-membrane Proteins
- Glycoprotein and Glycolipids
- Protein/Lipid with a short carbohydrate chain attached
- Protrudes from the bilayer
- Forming surface antigens
- Recepters in cell signalling
- Form h bonds with water stabilising the membrane
- Protrudes from the bilayer
- Protein/Lipid with a short carbohydrate chain attached
- Cholesterol
- Hydrophilic and hydrophobic regions
- Allows cholesterol to bind to phospholipids
- Preventing membrane being too fluid
- Prevents fatty acids crystalising
- Keeping the membrane fluid
- Allows cholesterol to bind to phospholipids
- Hydrophilic and hydrophobic regions
- Biological Membranes
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