AS Biology - Membranes

AS Biology - Membranes
Covering:
Structure,
Function,
Transport

Transcript

2. Function • Controls what substances enter and leave the cell • Cell membranes are partially permeable • They allow some smaller substances (oxygen) in but stop bigger substances (glucose) from entering
3. Structure (Phospholipids) • Phospholipid bilayer • The inner layer of phospholipids have their phosphate head pointing towards the cytoplasm in the cell • The outer layer of phospholipids have their phosphate head pointing towards the water surrounding the cell in tissues • The hydrophobic fatty acid tails point towards each other in the centre of the membrane • Phospholipid component allows lipid soluble molecules across but not water soluble molecules
4. Structure (Proteins) • Intrinsic proteins run through the membrane, extending across both layers of phospholipids • These are sometimes carriers of water soluble molecules • Others allow active transport ions across by forming channels • Extrinsic proteins are attached to only one surface of the bilayer • Form recognition sites • Identify cells and receptor sites for hormone attachment
5. Structure (other) • Cholesterol – regulates fluidity by making the membrane more rigid and stable • Glycoproteins and glycolipids – involved in cell to cell recognition and some act as hormones • Carbohydrates – layer around the membrane is made of carbohydrates and is called the glycocalyx
6. Fluid mosaic model • Fluid – the phospholipids in the membrane move relative to one another • Mosaic – different shapes and sizes of proteins in the membrane
7. Permeability • Lipid soluble substances (Vitamin A) and small molecules (Oxygen) dissolve in the phospholipids and diffuse across the membrane • Lipids “wip” through because they dissolve in phospholipids • Water soluble substances (Glucose) pass trough intrinsic proteins, that form water filled channels, and across the membrane
8. Cyanide • Respiratory inhibitor • Prevents mitochondria from producing ATP • No ATP = no active transport across the membrane
10. Diffusion • The movement of molecules from an area of high concentration to an area of low concentration • Molecules down the concentration gradient • Passive process • It doesn’t need energy
11. Facilitated diffusion • Passive process • Molecules move down the concentration gradient however they need “help” to transverse the membrane • They bind to a intrinsic protein which undergoes conformational change • Carries the molecule through the membrane
12. Facilitated diffusion – water soluble molecules • Water soluble molecules and ions can diffuse across the membrane through carrier proteins • Inside the carrier protein is a hydrophilic channel which attracts hydrophilic molecules
13. Active transport • Active process • Requires energy in the form of ATP • ATP – Active Transport Proteins • Pump expended energy to pump substrates to a higher concentration • Molecules move from a low concentration to a high concentration • Move against the concentration gradient
14. Osmosis • Passive process • Movement of water molecules from a high water potential to a low water potential • Move through a semi-permeable membrane
15. Water potential • Water moves from a high water potential to a low water potential • Calculated by Solute potential + Pressure potential • Solutions with a high water potential have less sugar and are hypotonic • Solutions with a low water potential have more sugar and are hypertonic
16. Vesicles • When there is a large amount of material to transport, membranes can form micro-containers called vesicles • They are from the plasma membrane itself • The process of formation and their movement is called cytosis
17. Exocytosis • Transports a large amount of material out of the cell • Proteins packaged by the golgi body and sent to the membrane to exit the cell
18. Endocytosis • Transport a large amount of material into the cell • Phagocytosis – cell engulfing solid material/bigger molecules • White blood cells engulf foreign bodies • Pinocytosis – cell takes in liquid material/smaller molecules