Cell Transport - A powerpoint presentation, Study notes of Biology

Download Cell Transport - A powerpoint presentation and more Study notes Biology in PDF only on Docsity! Cell Transport Lesson 4 General Biology 1 STEM Strand UST SHS Topic Outline I. Membrane’s Selective Permeability II. Passive Transport A. Simple Diffusion B. Facilitated Diffusion C. Osmosis IV. Active Transport A. Ion pumps (Electrogenic pumps) B. Coupled Transport V. Bulk Transport A. Exocytosis B. Endocytosis Plasma Membrane • It exhibits selective permeability, allowing some substances to cross it more easily than others, regulating the cell’s molecular traffic in order to maintain homeostasis. • It is a fluid mosaic of phospholipids and proteins Phospholipids • are the most abundant lipid in the plasma membrane • are amphipathic molecules, containing hydrophobic and hydrophilic regions Phospholipid bilayer Hydrophobic regions of protein Hydrophilic regions of protein The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it Transport Proteins • Transport proteins allow passage of hydrophilic substances across the membrane. • A transport protein is specific for the substance it moves. Examples: a) channel proteins b) carrier proteins a) Channel proteins • They have a hydrophilic channel that certain molecules or ions can use as a tunnel Examples: 1. Aquaporins, for facilitated diffusion of water between cells 2. Ion channels that open or close in response to a stimulus (gated channels). b) Carrier proteins • They bind to molecules and change shape to shuttle them across the membrane. • e.g. GLUT1 (glucose transporter 1) facilitates the transport of glucose across the plasma membranes of mammalian cells • Understanding how metabolism works in cells begins with the behavior of solutions. • How much of a solute is dissolved in a given amount of fluid is the solute’s concentration. ? Concentration Gradient • The difference in solute concentration between adjacent regions of solution is called the concentration gradient. High concentration  Low concentration • Solute molecules or ions tend to move “down” (HL) their concentration gradient because molecules are always in motion • They collide at random and bounce off one another millions of times each second. 1. Simple Diffusion • Movement along the concentration gradient (H  L) • No cell energy (ATP) required • For smaller molecules (e.g. O2, CO2, H2O *, nonpolar molecules) *Note that facilitated diffusion of water can also occur through the use of channel proteins called aquaporin (ex. Cells of the renal tubule, secretory glands and red blood cell before diffusion after diffusion 2. Facilitated Diffusion • In facilitated diffusion, transport proteins speed the passive movement of large molecules across the plasma membrane • Facilitated diffusion is still passive because the solute moves down its concentration gradient from a High to Low concentration • Ions and water through channel proteins • Glucose and amino acids through carrier proteins Transport proteins: a) Channel proteins b) Carrier proteins EXTRACELLULAR FLUID Channel protein A channel protein Solute CYTOPLASM Solute Carrier protein A carrier protein: shape change Osmosis is the diffusion of water across a selectively permeable membrane. Before Osmosis After Osmosis See next slide for the animation of this figure. 3. Osmosis Osmosis © -Water C)-Sugar 7 Permeable Membrane ° 50 2; 0 ae) o I 'O° O ° ° oO _,; O o ' oO o.6UCN dC 8 oO} oO 0 2 oI n, OQ Po O°} O° o 600 Low Sugar Concentration High Sugar Concentration High Water Concentration Low Water Concentration Lower concentration of solute (sugar) Osmosis H2O Higher concentration of sugar Selectively permeable membrane Same concentration of sugar Osmosis Water moves from L  H (solute) Note: More Solute means LESS water; Less Solute means MORE Water 1. Isotonic Solution • If a plant cell and its surroundings are isotonic, there is no net movement of water into the cell; the cell becomes flaccid (limp). “flaccid” 2. Hypertonic Solution • it contains a higher concentration of solute than that of the inside of the cell. inside the cell Red blood cells Plant cell 2. Hypertonic Solution • In a hypertonic solution, the cell looses water, and experiences shrinking of the cell’s cytoplasm due to excessive exit of water. • This is known as plasmolysis (in plants) / crenation (in animals) Red blood cells Plant cell Copyright © 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part, except for use as permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use. Turgor SUMMARY of Osmosis: Three Types of Solutions Hypotonic solution (a) Animal cell (b) Plant cell H2O Lysed H2O Turgid (normal) H2O H2O H2O H2O Normal Isotonic solution Flaccid H2O H2O Shriveled Plasmolyzed Hypertonic solution Osmoregulation • Hypertonic or hypotonic environments create osmotic problems for organisms. • Osmoregulation, the control of water balance, is a necessary adaptation for life in such environments. • The protist Paramecium, which is hypertonic to its freshwater environment, has an adaptation: a contractile vacuole that acts as a water pump. A. Ion pumps • Primary active transport system • Are trans-membrane protein molecules using energy (ATP) to transport ions across a plasma membrane against their concentration gradient How Ion Pumps Maintain Membrane Potential • Membrane potential is the voltage difference across a membrane. • Voltage is created by differences in the distribution of positive + and negative - ions on the two sides of the membrane. • An electrogenic pump is a primary transport protein that generates voltage across a membrane. It helps store energy that can be used for cellular work. Examples • Ca2+ pump • Na+K+ pump • Proton pump (H+) An electrogenic pump is a primary transport protein that generates voltage across a membrane. It helps store energy that can be used for cellular work. Extracellular fluid with high wa 2 Y concentration of Nat Na Vy. oy & r % The sodium-potassium pump Sodium ions (Na*) are pumped out of the cell and potassium ions (K*) are pumped into the cell. Cell membrane The energy to drive the pump is released by hydrolysis of ATP. Intracellular fluid with low concentration of Nat* and high concentration of Kt Copyright © 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part, except for use as permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use. Sodium–Potassium Pump Proton Pump (H+) • The main electrogenic pump of plants, fungi, and bacteria is a proton pump, which actively transports protons (H+) out of the cell. • The pumping of H+ transfers positive charge from the cytoplasm to the extracellular solution . • Small molecules and water enter or leave the cell through the lipid bilayer or by transport proteins. • Large molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesicles. • Bulk transport across the plasma membrane occurs by exocytosis and endocytosis; it requires energy. IV. Bulk Transport A. Exocytosis (large molecules out) • In exocytosis, transport vesicles migrate to the membrane, fuse with it, and release their contents outside the cell. • Many secretory cells use exocytosis to export their products. B. Endocytosis (large molecules in) • In endocytosis, the cell takes in macromolecules by forming vesicles from the plasma membrane. • Endocytosis is a reversal of exocytosis, involving different proteins. • There are three types of endocytosis: – Phagocytosis (“cellular eating”) – Pinocytosis (“cellular drinking”) – Receptor-mediated endocytosis 3. Receptor-Mediated Endocytosis • In receptor-mediated endocytosis, binding of ligands to receptors triggers vesicle formation. • A ligand is any molecule that binds specifically to a receptor site of another molecule using shape match. END