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Module 3

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Western University
Physiology 2130
Anita Woods

Module 3 - No exam questions based on cell organelles o Golgi – packaging and production of secretory vesicles and storage vesicles (lysosomes) o ER – site for the production, transport and storage of lipid molecules and proteins  RER – proteins; SER- lipids o Nucleolus – contains the DNA that produces the RNA found in ribosomes - Cell membrane – selectively permeable – two way traffic for nutrients and waste needed to enter/leave the cell, while it prevents the passage of other things between the intracellular and extracellular compartments o Made up of proteins to form channels and pores, carbohydrates for cell recognition and cholesterol for stability o Membrane spanning protein – embedded in phospholipid bilayer, span entire with of membrane – act as gates/channels – control movement of substances in/out of cell o Associated protein: structural – generally attached to the inside surface of the membrane – support and strengthens the membrane while others anchor cell organs to the intracellular side of the membrane o Associated protein: enzyme – act as catalysts for certain reactions immediately inside or outside the membrane o Cholesterol – found inserted in the non-polar lipid layer of the membrane – makes the membrane impermeable to some water soluble molecules and helps keep the membrane flexible over a wider temperature range o Carbohydrate – groups of carbs can be found associated with extracellular membrane proteins/lipids – form a protective layer called glycocalyx which plays a key role in the immune response of the cell and in recognition of other cells in the body o Hydrophobic (lipid/fatty acid) tail – oriented away from the aqueous and extra and intracellular solutions into the cell membrane – major barrier to water and water-soluble substances (ions, glucose, etc..) but fat soluble substances (oxygen, carbon dioxide, fatty acids and steroids) can penetrate this portion of the membrane with ease – dissolve through the lipid region of the membrane o Hydrophilic head – phosphate group – face out into the water base solutions inside and outside of the cell o When many phospholipids are thrown into water – form a lipid bilayer - Membrane proteins: o Receptors for the attachment of chemical hormones and neurotransmitters o Enzymes that help with chemical reactions or breakdown molecules o Ion channels or pores that allow water soluble substances, like ions, into cell o Membrane-transport carriers that transport molecules across the membrane (may include gated channels) o Cell-identity markers – ex. Antigens or glycoproteins – antigens are foreign particles that can stimulate the immune system - Membrane transport: o Endocytosis/exocytosis through vesicles (pinocytosis for small molecules) o Diffusion through the lipid bilayer (fat soluble molecules)  Diffusion of molecules moves from high to low concentrations due to the molecule’s random thermal motion (See example 3.9) – continues to move until the concentration is uniform and the net movement is zero  equilibrium but the molecules are still moving about randomly  Electrically charged molecules tend towards areas of opposite charge (down an electrical gradient) – charged ions can move both their chemical concentration and electrical gradient – if these are in opposite directions – movement depends on the balance of the 2 gradients and stop moving once these reach electrochemical equilibrium (electrical force is equal to and in opposite direction to the chemical force) – if the 2 forces equal in magnitude but in opposite directions and there is no net movement = electrochemical equilibrium o Diffusion through protein channels (water-soluble molecules)  Pores are quite specific and will generally allow only one type of ion through  Movement is limited by the size of the protein channel (~0.8 m – sugar too large), the charge of the molecule (proteins that make up the channel also have charges on them, positive ion will not go through a positively charged channel)  The greater the electrochemical gradient of a molecule, the greater its rate of movement through channels  Number of channels in the membrane affect its rate – even if there is a large concentration gradient, will not move across a membrane unless there are channels for it (more channels = more ions diffusing) o Facilitated diffusion – other water soluble substances (sugar) that is too large for protein channels – attach to specific protein carrier on membrane and cause a change in protein’s shape – causes either an opening of channel through which molecule passes or the protein rotates the molecule to the inner surface of the membrane where it is released  Does not require energy  Differs from regular diffusion because is limited by the number of available proteins- when all carriers occupied and working, becomes saturated and can no longer operate any faster  The speed that the carrier can change shape/configuration is limited  FD shows chemical specificity (carrier protein will only interact with a specifically shaped molecule) and may be competitively inhibited by molecules similar in shape o Active transport – like facilitated diffusion – can be saturated, shows chemical specificity and shows competitive inhibition  Uses ENERGY – move molecules up their gradient – ex. The sodium- potassium pump – energy comes from splitting ATP into ADP and Pi - Most abundant substance to diffuse is water – requires special pores – amount that diffuses into cells normally exactly the amount that diffuses out – volume of cells remains constant o Under certain conditions it is possible for a concentration difference to occur (ex. Adding a solute that c
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