BGY3002 Lecture 3: Endomembrane System & Plasma Membrane PDF

Endomembrane System BGY3002 By: Assoc Prof Dr Mashitah SM Learning outcomes: Describe the structure of Endoplasmic Reticulum and its role in endomembrane system Compare the difference between Rough Endoplasmic Reticulum and...

Endomembrane System BGY3002 By: Assoc Prof Dr Mashitah SM Learning outcomes: Describe the structure of Endoplasmic Reticulum and its role in endomembrane system Compare the difference between Rough Endoplasmic Reticulum and Smooth Endoplasmic Reticulum Describe the structure and importance of Golgi complex Role of Golgi complex in secretory pathway Differentiation between Endocytosis, Pinocytosis and Phagocytosis Define lysosomes, explanation of its structure and function Explain the structure, function and role of Ribosomes in protein synthesis  Endomembrane - composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell (wiki) Organelles of the endomembrane system: nuclear membrane endoplasmic reticulum Golgi apparatus Lysosomes Vacuole call Plasma membrane  Endomembrane - composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell (wiki) Function - manufactures membranes & performs many bio-synthesis functions Structure membrane connected to nuclear envelope & extends throughout cell about 50% membranes in eukaryotic cell rough ER = bound ribosomes smooth ER = no ribosomes Rough ER bumpy ribosomes attached to its cytoplasmic surface ribosomes make proteins - forming protein chains into the lumen RER also makes phospholipids for other cellular membranes also helps modify proteins that will be secreted from the cell  Smooth ER Factory processing operations - many metabolic processes - synthesis & hydrolysis - enzymes of smooth ER; synthesize lipids, oils, phospholipids, steroids & sex hormones hydrolysis (breakdown) of glycogen (in liver) into glucose detoxify drugs & poisons (in liver) In muscle cells, special smooth ER called the sarcoplasmic reticulum (surrounds each myofibril – stores and releases calcium Endocytic pathways Golgi apparatus found in both plant and animal cells Function- packaging the protein/chemical products Lysosomes contains digestive enzymes and acts as the organelle-recycling facility of an animal cell breaks down old and unnecessary structures –reused Example - white blood cells called macrophages Vacuoles - Plants cells stores water and wastes wastes, isolates hazardous materials, and has enzymes that can break down macromolecules and cellular components - function in water balance Peroxisomes enzymes involved in oxidation reactions, - produce hydrogen peroxide as a by- product If you do not water your house plants, they will first wilt, then eventually die. Why do wilting and dying not occur at the same time? PLASMA MEMBRANE AND FUNCTIONS LO’s: Able to EXPLAIN about: - roles of plasma membrane in cellular functions - fluid mosaic of phospholipids and proteins - transportation of molecules across membrane - exocytosis and endocytosis  The chronology Gorter & Grendel Davson & Danielli Singer & Nicolson (1925) (1935) (1960-70s) Found that lipid Overton (1890s) molecules can The fluid mosaic form bilayers, and Suggested the existence of a model that the surface Discover the area of the layer of globular (i) The core lipid chemical nature monolayer proteins on the bilayer exists in a of the cell’s outer extracted from external and fluid state, layer the cells is internal surfaces capable of Studied the rate approximately of the membrane dynamic of diffusion across equal to twice the Also the existence movement membrane  surface area of of protein-lined (ii) Membrane Cell’s outer the cells pores that extend proteins form a barrier has lipid- (ii) The polar head across the mosaic of soluble groups are membrane (f(x) particles characteristic. directed towards for the movement penetrating the the aqueous side of polar solutes lipid to varying (outside) of the and ions across degrees bilayer cell boundaries)  Membrane Functions Protection Communication Selectively allow substances in Respond to environment Recognition  Arranged as a Phospholipid bilayer Cell membrane separates living cell from aqueous environment – thin barrier = 8nm thick Controls traffic in & out of the cell – allows some substances to cross more easily than others hydrophobic (nonpolar) vs. hydrophilic (polar) Permeability to polar molecules? Membrane becomes semi-permeable via protein channels – specific channels allow specific material across cell membrane Fluid-Mosaic Model Molecule Movement & Cells polar hydrophilic Phosphate heads Passive Transport Active Transport nonpolar Hydrophobic hydrocabon tails Endocytosis Exocytosis polar hydrophilic Phosphate heads Amphipathic  Proteins— For Function Transport Receptors Enzymes Signal Transducers Support  CELL MEMBRANE IS MORE THAN LIPIDS… Transmembrane proteins embedded in phospholipid bilayer – create semi-permeabe channels lipid bilayer protein channels membrane in lipid bilyer membrane  Passive Transport No energy required Move due to gradient – differences in concentration, pressure, charge Move to equalize gradient – High moves toward low Types of Passive Transport Diffusion Osmosis Facilitated diffusion  the net movement of a Diffusion substance (liquid or gas) from an area of higher concentration to one of lower concentration. Molecules move to equalize concentration stops at equilibrium (when the concentrations across a membrane are equal Gas exchange in lungs by diffusion  Osmosis Special form of diffusion Fluid flows from lower solute concentration Often involves movement of water – Into cell – Out of cell OSMOTIC PRESSURE Permeability of the Cell Membrane  Diffusion through phospholipid bilayer What molecules can get through directly? – fats & other lipids lipid  What molecules can inside cell NOT get through NH3 salt directly?  polar molecules  H2O  ions (charged)  salts, ammonia sugar aa H2O outside cell  large molecules  starches, proteins  Facilitated Diffusion Differentially permeable membrane Channels help molecule or ions move Usually by transport proteins of cells No energy is used Solving these problems Mechanisms by which cells solve the problem of transporting ions and small molecules across their membranes: 1) Facilitated diffusion Transmembrane proteins create a water-filled pore through which ions and some small hydrophilic molecules can pass by diffusion. The channels can be opened (or closed) according to the needs of the cell. 2) Active transport Transmembrane proteins, called transporters, use the energy of ATP to force ions or small molecules through the membrane against their concentration gradient. Process of Facilitated Transport Protein binds with molecule Shape of protein changes Molecule moves across membrane Plasma Membrane Proteins PROTEINS CAN MOVE IN THE MEMBRANE, TOO!  Passive or Active Transport Passive Active Passive Transport does Active Transport requires not require cell energy cell energy (ATP) Examples: Diffusion, Examples: Carrier Facilitated diffusion and mediated active Osmosis transport, Endocytosis and Exocytosis  How about large molecules? Moving large molecules into & out of cell – through vesicles & vacuoles – endocytosis phagocytosis = “cellular eating” pinocytosis = “cellular drinking” – exocytosis exocytosis  Process of Endocytosis Plasma membrane surrounds material Edges of membrane meet Membranes fuse to form vesicle Forms of Endocytosis Phagocytosis – cell eating Pinocytosis – cell drinking  Exocytosis Reverse of endocytosis Cell discharges material  SUMMARY Phospholipid Bilayer Fluid Mosaic Model Membrane Proteins Diffusion Facilitated Diffusion Osmosis Bulk Transport Active Transport