TRANSPORT ACROSS MEMBRANES
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This document provides an overview of transport across cell membranes. It begins with an introduction and defines the key components of the cell membrane. It then describes the main types of transport - passive diffusion, facilitated transport, osmosis, and active transport. Specific transport proteins and their roles are explained. The document also covers factors that affect the rate of transport and bulk transport mechanisms like endocytosis and exocytosis. In summary, the document serves as a guide to the various pathways and mechanisms by which substances move across the selective barrier of the cell membrane.
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TRANSPORT ACROSS MEMBRANES
- 1. TRANSPORT ACROSS MEMBRANES (BCH 857) ALUKO, Adeola ADESEJI, Wasiu AROGUNDADE, Tolulope GBADAMOSI, Ismail Course Lecturer: Dr. ARIISE
- 2. OUTLINE 2 Introduction The Cell Membrane Types of Transport Tonicity of Solutions Diffusion Facilitated Transport Osmosis Active Transport Factors Affecting Transport Across a Membrane Endocytosis and Exocytosis Summary and Conclusion
- 4. THE CELL MEMBRANE 4 Comprises phospholipids and proteins in ratio 3:2; Contains carbohydrate bound to protein as glycoprotein; Measures about 6.5-10nm in thickness; Has glycolipids and glycoprotein projecting outwards as glycocalyx; Contains pores measuring between 0.7-1.0亮 in diameter; Is selectively permeable.
- 6. 6 PASSIVE ACTIVE Passive diffusion is a spontaneous phenomenon that increases the entropy of a system and decreases the free energy. The transport process is influenced by the characteristics of the transport substance and the nature of the bilayer. In active transport a solute is moved against a concentration or electrochemical gradient, in doing so the transport proteins involved consume metabolic energy, usually ATP. TYPES OF TRANSPORT
- 7. TRANSPORT PROTEINS 7 Channel proteins are embedded in the cell membrane & have a pore for materials to cross. Carrier proteins can change shape to move material from one side of the membrane to the other.
- 8. TONICITY OF SOLUTIONS 8 The tonicity of a solution will affect the size & shape of cells: ISOTONIC SOLUTION: the solution concentration is equal on both sides of the membrane. HYPERTONIC SOLUTION: The solution outside the cell is more concentrated than inside. HYPOTONIC SOLUTION: The concentration inside the cell is more concentrated than outside.
- 10. So Should You Drink Sea Water??? 10
- 11. DIFFUSION 11 Requires NO energy. Molecules move from area of HIGH to LOW concentration. They have a natural KINETIC ENERGY.
- 12. DIFFUSION 12 Molecules diffuse until they are evenly distributed. EXAMPLES of molecules that easily cross cell membranes by simple diffusion are: oxygen, carbon dioxide, alcohols, fatty acids, glycerol, and urea.
- 13. FACILITATED TRANSPORT 13 Molecules will randomly move through the opening like pore, by diffusion. This requires no energy, it is a PASSIVE process. Molecules move from an area of high concentration to an area of low conc.
- 14. FACILITATED TRANSPORT 14 Each protein channel or protein carrier will allow only ONE TYPE OF MOLECULE to pass through it. Many channels contain a gate which control the channel's permeability.
- 15. OSMOSIS 15 Diffusion of water across a membrane. Moves from HIGH water potential (low solute) to LOW water potential (high solute).
- 16. OSMOSIS 16 To cross the membrane, water must move through a protein ion channel. In certain cellular conditions, these protein channels can be opened or closed (i.e. in the kidneys, large intestines) depending on how much water is needed by the body.
- 17. ACTIVE TRANSPORT 17 Molecules move against the concentration gradient. Requiresenergy 1. Solute Pumps (Na+-K+-ATPase pump) mostly in nerve membranes. 2. Bulk Transport.
- 18. FACTORS AFFECTING MOVEMENT ACROSS MEMBRANES 18 The rate of diffusion will be increased when there is : 1. Concentration: the difference in concentration between two areas (the concentration-gradient) causes diffusion. The greater the difference in concentration, the faster the diffusion. 2. Molecular size: smaller substances diffuse more quickly. Large molecules (such as starches and proteins) simply cannot diffuse through. 3. Shape of Ion/Molecule: a substances shape may prevent it from diffusing rapidly, where others may have a shape that aids their diffusion.
- 19. FACTORS AFFECTING MOVEMENT ACROSS MEMBRANES 19 4. Viscosity of the Medium: the lower the viscosity, the more slowly molecules can move through it. 5. Movement of the Medium: currents will aid diffusion. Like the wind in air, cytoplasmic steaming (constant movement of the cytoplasm) will aid diffusion in the cell. 6. Solubility: lipid - soluble molecules will dissolve through the phospholipid bilayer easily, as will gases like CO2 and O2. 7. 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.
- 20. BULK TRANSPORT 20 Endocytosis (Pinocytosis) Pinocytosis (cell drinking): small molecules are ingested and a vesicle is immediately formed. This is seen in small intestine cells (villi)
- 21. BULK TRANSPORT 21 Endocytosis (Phagocytosis) phagocytosis (cell eating): large particles, (visible with light microscope) are invaginated into the cell (e.g. white blood cells eat bacteria).
- 22. BULK TRANSPORT 22 Endocytosis (Receptor-Mediated) Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol, etc.
- 25. 25
Editor's Notes
- #5: The cell membrane (or plasma membrane or plasmalemma) surrounds the油cytoplasm油of living cells, physically separating the油intracellular油components from the油extracellular油environment.
- #6: Permeable- ability to pass through a membrane Impermeable- cant pass through Selectively Permeable (semipermeable)- some things can pass through and some cant The cell membrane is油selectively permeable油and able to regulate what enters and exits the cell, thus facilitating the油transport油of materials needed for survival. The cell membrane thus works as a selective filter that allows only certain things to come inside or go outside the cell. The cell employs a number of transport mechanisms that involve biological membranes:
- #7: 油The movement of substances across the membrane can be either "passive", occurring without the input of cellular energy, or "active", requiring the cell to expend energy in transporting it.
- #8: A油transport protein油(variously referred to as a油transmembrane pump,油transporter protein,油escort protein,油acid transport protein,油cation transport protein, or油anion transport protein) is a油protein油that serves the function of moving other materials within an油organism. Transport proteins are vital to the growth and life of all living things. There are several different kinds of transport proteins.
- #14: Some molecules are not normally able to pass through the lipid membrane, and need channel or carrier proteins to help them move across. This does not require energy when moving from [H] to [L] (with the concentration gradient). Molecules that need help to move through the plasma membrane are either charged, polar, or too large.
- #15: When the gate is open, the channel transports, and when the gate is closed, the channel is closed. These gates are extremely important in the nerve cells
- #18: EXAMPLES of molecules that move this way are all of the things that require protein carriers to move across the plasma membrane. ions (like Na+ and K+ in cells, and iodine) and sugars, amino acids, nucleotides...
- #19: Non-polar molecules diffuse more easily than polar molecules because they are soluble in the non polar phospholipid tails.
- #20: Non-polar molecules diffuse more easily than polar molecules because they are soluble in the non polar phospholipid tails.
- #25: Just like the whole organism needs some substances taken in to survive, so do cells too Everything that is transported across the cell membrane takes place by one of two fundamental processes.