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Transport across cell membrane
- 2. Types of cellmembrane transport Factors affecting transport Cell membrane Chemical gradient Electrical gradient Rate of transport Passive transport Diffusion Osmosis Facilitated diffusion Active transport Pumps phagocytosis Endocytosis/exocytosis
- 3. Factors affecting transport:cell membrane The cell needs to absorb and excrete various compounds throughout its life. These compounds need to pass through the membrane which is made from a phospholipid bilayer The phospholipid bilayer is formed by phospholipid molecules bipolar molecule: the fatty acid side is hydrophobic, the phosphoric side is hydrophilic
- 4. Factors affecting transport:Chemical gradient Compound moves from an area of high concentration to low concentration (or concentration gradient) All compounds permeable to the phospholipid bilayer will move this way
- 5. Factors affecting therate of transport The rate of transport will depend on: The concentration gradient The compound permeability to the membrane The type and number of charges present on the compound
- 6. Passive transport Compounds willmove from area of high concentration toward area of lower concentration No ATP is needed for this type of transport Passive transport mainly TWO types A-Osmosis B-Diffusion-diffusion again two types a-simple diffusion- no energy needed b- facilitated diffusion- no energy needed -help through a protein channel
- 7. Osmosis Each compoundobeys the law of diffusion diffusion of water from HIGH concentration of water to LOW concentration of water across a semi-permeable membrane However, some compounds are unable to cross the cell membrane (glucose, electrolytes…) Water can cross will enter or exit the cell depending its concentration gradient.
- 8. Diffusion Simple diffusion- noenergy needed Movement across higher to lower concentration gradient. Facilitated diffusion- Some compounds are unable to diffuse through the membrane. They will be allow to cross if the membrane has proteins that can bind these compounds and enable to cross toward the area of lower concentration
- 9. Simple andfacilitated diffusion inside cell outside cell lipid inside cell outside cell H2O simple diffusion facilitated diffusion H2O protein channel
- 10. Simple Diffusion Doesn’trequire energy Moves high to low concentration Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out.
- 11. The rate ofdiffusion will be increased when there is : Concentration: the difference in between two areas (the gradient) causes diffusion. The greater the difference in concentration, the faster the diffusion. Molecular size: smaller substances diffuse more quickly. Large molecules (such as starches and proteins) simply cannot diffuse through. Shape of Ion/Molecule: a substance’s shape may prevent it from diffusing rapidly, where others may have a shape that aids their diffusion. Viscosity of the Medium: the higher the viscosity, the more slowly molecules can move through it.
- 12. Movement of theMedium: currents will aid diffusion. Like the wind in air, cytoplasmic streaming (constant movement of the cytoplasm) will aid diffusion in the cell. Solubility: lipid - soluble molecules will dissolve through the phospholipid bilayer easily, as will gases like CO2 and O2. Polarity: water will diffuse, but because of its polarity, it will not pass through the non-polar phospholipids. Instead, water passes though specialized protein ion channels
- 13. Facilitated diffusion Doesn’t requireenergy Uses transport proteins to move high to low concentration Examples: Glucose or amino acids moving from blood into a cell.
- 14. Active Transport - Pumps -phagocytosis - Endocytosis/exocytosis
- 15. Active transport ATP (energy)is needed pump Moves materials from LOW to HIGH concentration AGAINST concentration gradient
- 16. Endocytosis Endocytosis: (“Endo”means “in”). Endocytosis is the taking in of molecules or particles by invagination of the cell membrane forming a vesicle. Integrity of plasma membrane is maintained. This requires energy. Endocytosis is fallowed by exocytosis on the other side. – Transcytosis, vesicle trafficking, or cytopempsis.
- 17. There are twotypes of endocytosis 1. pinocytosis (cell drinking): small molecules are ingested and a vesicle is immediately formed. This is seen in small intestine cells (villi) 2. phagocytosis (cell eating): large particles, (visible with light microscope) are invaginated into the cell (ie: white blood cells ‘eat’ bacteria
- 18. Exocytosis Exocytosis: (“Exo”means “out”.) Exocytosis is the reverse of endocytosis. This is where a cell releases the contents of a vesicle outside of the cell. These contents may be wastes, proteins, hormones, or some other product for secretion. This also requires energy. Example: vesicles from the Golgi fuse with the plasma membrane and the proteins are released outside of the cell.
- 19. Membrane Transport Proteins 1.Water Channels or Aquaporins (AQPs) – 12 types Amount of water is regulated by No. of AQPs They are known as gated channel although they are pores. Two types a) Aquaporins- only water. b) Aquaglyceroporins- also for small molecules.
- 20. 2- Ion Channels- All cells specially on excitable cells – Neurons and muscle cells Gated – voltage gated and extracellular agonist or antagonist gated ex – acetylcholine gated cationic specific channel at motor end plate of skeletal muscle. Ex- Na, K, Ca, Cl, Anion , cation.
- 21. 3.Solute Carriers- threegroups-1. Uniporters- single molecule across the membrane (GLUT ) 2. Symporters- Two or more molecules Ex- Na-k-cl Symporter (Kidney) Na - Glucose Cotransporter. 3. Antiporters- Two or more molecules in opposite directions Ex :Na- H antiporter ( PH regulation) , Cl- HCO3 antiporter
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