Types of Transport Mechanisms Across Cell Membranes PDF
Document Details
Uploaded by FlexibleMarimba
RAK Medical & Health Sciences University
Prof. Tarig Hakim Merghani
Tags
Summary
This document is a lecture presentation on types of transport mechanisms across cell membranes. It explains passive transport, such as simple diffusion and facilitated diffusion, and active transport, including co-transport and antiport. Numerous diagrams and examples are included.
Full Transcript
Types of Transport Mechanisms Across Cell Membranes Prof. Tarig Hakim Merghani Learning outcome By the end of this session you will be able to: Compare and discuss the types of transport mechanisms across cell membranes (passive and active transport mechanisms) The cell membrane A...
Types of Transport Mechanisms Across Cell Membranes Prof. Tarig Hakim Merghani Learning outcome By the end of this session you will be able to: Compare and discuss the types of transport mechanisms across cell membranes (passive and active transport mechanisms) The cell membrane A phospholipid bilayer with proteins. The proteins (integral or peripheral) can act as channels, carriers, pumps, enzymes, receptors, etc. The cell membrane Semi-permeable (allows passage of lipid-soluble substances and prevents passage of water and water-soluble ones) The cell membrane The protein channels and carriers facilitate passage of water and water-soluble substances. Transport mechanisms across cell membranes Passive No energy is needed Active Require energy Passive transport mechanisms Simple diffusion Facilitated diffusion Others Simple diffusion Transport of a substance from its side of higher concentration to a side of lower concentration (i.e., down the concentration gradient or electrical gradient) Energy is not needed Protein carriers are not needed Simple diffusion follows Fick’s law of diffusion (J = - DA * ΔC/ΔX) J= net flux of solute particles (or diffusing tendency) D= Diffusion coefficient A= surface area that is available for diffusion ΔC= difference in concentration ΔX= Thickness ΔC/ ΔX= concentration gradient Net flux= - Diffusion coefficient x Surface area x Conc. gradient Examples of simple diffusion Certain substances diffuse directly through the lipid bilayer. Certain substances diffuse through protein channels passively (can be considered as facilitated diffusion). Examples of simple diffusion Diffusion of: Lipids and lipid-soluble substances Gases (O2 & CO2) (= Non-polar substances) Diffusion through protein channels: water and water-soluble substances (= Polar substances) Facilitated diffusion Differs from simple diffusion in that protein carriers are needed. Facilitated diffusion Have a maximum rate of transport (Tmax) that depends on the number of carriers The maximum rate is reached when all the carriers are saturated Tmax (when all carriers are saturated) Examples of facilitated diffusion Transport of glucose and amino acids in the kidney and intestine (through the basolateral membrane). Active transport mechanisms The transport of a substance from an area of lower concentration to an area of higher concentration (i.e., against the concentration or electrical gradient) Active transport mechanisms Energy is needed Protein pumps are needed Types of active transport (Primary) active transport Secondary active transport Exocytosis Endocytosis (Primary) active transport A substance is transported against its chemical or electrical gradient, with consumption of energy and usage of a carrier. Secondary active transport A substance is transported against its gradient, in association with another (driving) substance that is transported down its gradient. Secondary active transport The transport may occur in the same direction as the driving substance (= symport or co-transport), or in the opposite direction (= antiport) Example of primary active transport The Sodium-Potassium Pump Example of secondary active transport Co-transport: Glucose Antiport: Hydrogen Exocytosis For secretion of proteins synthesized within the cell Exocytosis steps A granule or vesicle moves to cell membrane Its membrane fuses with cell membrane The area of fusion breaks down The contents of the granule or vesicle are left outside (while the cell membrane remains intact) Endocytosis The reverse of exocytosis. Two types: Phagocytosis (Cell eating) For solid substances like bacteria Pinocytosis (Cell drinking) For soluble substances