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BIOL190: Cell Membrane Structure & Function (WEEK 6: 10/6 class)

by: Talia Douglas

BIOL190: Cell Membrane Structure & Function (WEEK 6: 10/6 class) BIOL190 (Intro to Biology for the Health Professions)

Marketplace > Towson University > Biology > BIOL190 (Intro to Biology for the Health Professions) > BIOL190 Cell Membrane Structure Function WEEK 6 10 6 class
Talia Douglas
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These notes cover information about the cell membrane, its structure, and function. This section is also included on the study guide that I have uploaded but these notes go more in depth on this to...
Intro to Biology for the Health Professions
Class Notes
BIOL190, Biology, health, Professions, BIOL




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This 8 page Class Notes was uploaded by Talia Douglas on Thursday October 6, 2016. The Class Notes belongs to BIOL190 (Intro to Biology for the Health Professions) at Towson University taught by in Fall 2016. Since its upload, it has received 45 views. For similar materials see Intro to Biology for the Health Professions in Biology at Towson University.

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Date Created: 10/06/16
NOTES: CELL MEMBRANE STRUCTURE AND FUNCTION Hi Class! These notes are composed of important information from the  Campbell Biology book sections: 4.16, 4.19­4.21, 5.1­5.9, and  11.10. I have also posted my study guide that reviews some of  these notes, but these notes are more in depth on the subject.   Highlight key: Yellow Highlight: ME talking Purple Highlight: Definitions Underlined: Very important things to remember 4.16 THE CELL’S INTERNAL SKELETON HELP ORGANIZE ITS STRUCTURE & ACTIVITIES Cytoskeleton: Networks of protein fibers extended throughout a  cell  Plays an important role in organizing structures and  activities in the cell  Provides structural support Movement and motility  Contain 3 main kinds of fibers o Microtubules: straight and hollow tubes composed of  globular proteins called tubulins; the thickest fiber  Centrosome: Contains a pair of centrioles composed of a ring of microtubules. o Microfilaments (Actin Filaments): solid rods composed  of mostly globular proteins (actin) that are shaped in  a twisted double chain; the thinnest fiber o Intermediate filaments: Made of various fibrous  proteins that supercoil into cables; between thick and  thin fibers  Found in the cells of most animals  (Additional info. The nucleus typically sits in a  cage made of intermediate filaments.) 4.19  THE EXTRACELLULAR MATRIX OF ANIMAL CELLS FUNCTIONS IN SUPPORT AND REGULATION What is an extracellular matrix? NOTES: CELL MEMBRANE STRUCTURE AND FUNCTION An elaborate layer that animal cells produce that help hold  cells together in tissues.  Protects and supports plasma membrane  Components: glycoproteins (proteins bonded with  carbohydrates) such as collagen with is 40% of the protein  in your body.   Can regulate a cell’s behavior influencing the activity of  genes through signals. How does it work?  ECM may attach to the cell through other glycoproteins that  bind to integrins.   Integrins: membrane proteins that span the membrane and  attach to the other side of proteins connected to  microfilaments in the cytoskeleton. o  Function: Integration­ transmits signals between ECM  and cytoskeleton.  4.20  THREE TYPES OF CELL JUNCTIONS IN ANIMAL TISSUES What are cell junctions for?  The junctions are to increase the surface area for  absorption of nutrients. Types of Cell Junctions:  Tight junctions: A junction where the plasma membrane of  neighboring cells come tightly together by proteins. o Prevents leakage of fluid such as contents of the  digestive tract leaking into surrounding tissue.  Anchoring Junctions: This junction function like rivets,  fastening cells together into strong sheets. o Intermediate filaments anchor this junction into the  cytoplasm. o Common in tissues subject to stress such as skin and  muscle.  Gap Junctions (Communicating Junctions): Channels that allow small molecules to flow through protein­lined pores between  cells. o Common in embryos, where communication between cells is essential for development.  4.21  NOTES: CELL MEMBRANE STRUCTURE AND FUNCTION CELL WALLS ENCLOSE AND SUPPORT PLANT CELLS What is a cell wall?  Cell Wall: A rigid, extracellular structure that protects  cells and provides skeletal support. o One of the features that distinguish plant cells from  animal cells. o When a cell stops growing, it strengthens its wall.  Plasmodesmata: Numerous channels that connect adjacent plant cells. 5.1  MEMBRANES ARE FLUID LIPIDS AND PROTEINS What is a fluid mosaic model? It is a diverse protein molecule suspended in a fluid  phospholipid bilayer. What is selective permeability? Allows some substances to cross more easily than others. Cell membrane regulates the exchange of materials. The different proteins in the membrane are: o Attachment proteins: support membrane and connected to  ECM and cytoskeleton. o Receptor proteins: signal reception and relay o Channel proteins: transport proteins that allow  specific molecules to enter and exit. o Junction proteins: intercellular joining o Glycoproteins: ID tag that can be recognized by the  membrane proteins of other cells. o Enzymes: proteins that speed up reactions. 5.2  FORMATION OF MEMBRANES: CRITICAL STEP IN ORIGIN OF LIFE Phospholipids  The key ingredients of biological membranes  First organic molecules that formed from chemical reactions  on early Earth Can spontaneously self­assemble into simple membranes 5.3  PASSIVE TRANSPORT IS DIFFUSION ACROSS MEMBRANE WITH NO ENERGY INVESTMENT NOTES: CELL MEMBRANE STRUCTURE AND FUNCTION What is diffusion? Diffusion is the tendency for particles of any substance to  spread out into the available space.  Most of the traffic across membranes occur by diffusion What is concentration gradient?  The movement of solutes  What is passive transport?  The movement of molecules diffusing across its membrane to  make a high concentration a lower concentration.   The reason why oxygen essential for metabolism enters the  cell and the reason why carbon dioxide which is metabolic  waste, leaves it.  Requires no energy.  5.4  OSMOSIS IS DIFFUSION OF WATER ACROSS A MEMBRANE What is Osmosis?  Diffusion of water across a selectively permeable membrane. Remember! Selectively permeable membranes allow some  substances to cross more easily than others. 5.5  WATER BALANCE BETWEEN CELLS AND THEIR SURROUNDINGS IS CRUCIAL What is tonicity?  Refers to the ability of a surrounding solution to cause a  cell to gain or lose water.  The tonicity of a solution depends on its concentration of  solutes relative to the concentration of solutes inside the  cell. What is an isotonic solution?  A solution where the cell’s volume remains constant.  The solute concentration of a cell and its isotonic  environment are essentially equal and the cell gains water  at the same rate that it loses it.  Red blood cells are transported into the isotonic plasma of  blood  Sea water is isotonic to cells of marine animals Normal cell solution What is a hypotonic solution? A solution with a solute concentration lower than that of  the cell NOTES: CELL MEMBRANE STRUCTURE AND FUNCTION  Cell gains water, swells and may burst  In hypotonic environment, a plant cell is very firm and in a healthy state for most plant cells. o Turgor pressure prevents the plant cell from taking in  too much water and bursting. What is a hypertonic solution?  A solution with a higher solute concentration.  Cells can shrivel in die from water loss.  In hypertonic environment, a plant cell loses water,  shrivels and its plasma membrane pulls away from the cell  wall. (Plasmolysis) What is osmoregulation? The way that organisms can regular the solute concentration  of its body fluids to prevent excessive uptake or water  loss. 5.6  TRANSPORT PROTEINS CAN FACILITATE DIFFUSION What is facilitated diffusion?  A type of passive transport that is the driving force of  concentration gradient.  Hydrophilic ions and molecules require this help to move  across a membrane  Who uses facilitated diffusion? o A number of sugars, amino acids, ions and even water! What is aquaporin? A protein channel that holds a very rapid diffusion of water into and out of cells. o Can be found in bacteria, plants and animals 5.7  DISCOVERY OF AQUAPORINS All about Aquaporins: Peter Agre discovered aquaporins  Discovered aquaporins by studying Rh blood antigens. He  worked out a method to isolate the Rh protein and his sample seemed to consist of two proteins. He originally thought  that the smaller protein was just a breakdown of the larger  one but turns out he was wrong.  Agre’s research team:  NOTES: CELL MEMBRANE STRUCTURE AND FUNCTION o  Made antibodies that would specifically bind to the  smaller protein.  o Results: The antibodies did not bind to any part of the Rh protein which indicates the smaller protein was not  part of the Rh protein. But it did bind to red blood  cells that proves that this new protein is abundant in  red cell membranes. o Determined that the protein was identical to certain  kidney cells. o Conducted an experiment to see if the protein might be  the elusive water channel that would explain the rapid  transport of water in cells.   Researchers injected messenger RNA for the protein into frog eggs whose cells are known to be water  impermeable.   Within 72 hours, the frog cells had translated the mRNA into the new protein.   Transferred a group of RNA­injected frog eggs and  a control group of eggs injected with only a  buffer solution to a hypotonic solution and  monitored them with videomicroscopy.   Results: The experimental egg cells exploded  within three minutes. The control eggs showed  minimal swelling.  Concluded that the newly discovered protein  enabled the rapid movement of water into the  cells. 5.8  CELLS EXPEND ENERGY IN ACTIVE TRANSPORT OF SOLUTE What is active transport?  Active transport: in active transport, a cell must expend  energy to move a solute across a membrane towards the side  where the solute is more concentrated. (concentration  gradient.)  Requires energy: ATP, the energy molecule, supplies the  energy for most active transport.  Allows a cell to maintain internal concentrations of small  molecules and ions that are different from concentrations in its surroundings. NOTES: CELL MEMBRANE STRUCTURE AND FUNCTION What about large molecules? We found out how water and small  solutes enter and leave cells so let’s talk about large  molecules! 5.9  EXOCYTOSIS AND ENDOCYTOSIS What is exocytosis?  Exocytosis: The process to export bulky materials such as  proteins or polysaccharides.  How does it occur? 1. A transport vesicle filled with macromolecules buds from  the Golgi apparatus and moves to the plasma membrane. 2. Once there, the vesicle fuses with the plasma membrane  and the vesicle’s contents spill out of the cell. What is endocytosis?  Endocytosis: A transport process through which a cell takes  in large molecules.  There are three types: o Phagocytosis: when a cell “eats” a particle by wrapping extensions (pseudopodia) around it and packages it  within a vacuole. o  How does it work?  1. It engulfs a particle by pseudopodia and  packages it within a vacuole.  2. The vacuole then fuses with a lysosome which  digest the contents of the vacuole. o Pinocytosis: when a cell “drinks” fluids by wrapping  the cell membrane around it and packaging it within a  vesicle. o How does it work?  1. It drinks a particle and packages it within a  vesicle. o Receptor­Mediated Endocytosis: Enables a cell to  acquire specific solutes.  o How does it work?  Receptor proteins are embedded in regions of the  membrane that are lined by a layer of coat  proteins.  The plasma membrane idents to form a coated pit  whose receptor proteins pick up particular  molecules from the extracellular fluid. NOTES: CELL MEMBRANE STRUCTURE AND FUNCTION  Coated pit pinches closed to form a vesicle which  then releases molecules into the cytoplasm.  YOUR CELLS use this process to take in cholesterol from the blood for synthesis of membranes and as a precursor for other steroids. 11.10  SIGNAL TRANSDUCTION What is a signal transduction pathway?  A series of molecular changes that convert a signal on a  target cell’s surface to a specific response inside the  cell.  How does it work? 1. The cell sends a message that secretes a signaling molecule. 2. The molecule then binds to a specific receptor protein that is embedded in the target cell’s plasma membrane. 3. The binding activates the first in a series of relay proteins  within the target cell. (Each relay molecule activates another.) 4. The last relay molecule in the series activates a  transcription factor 5. The transcription of a specific gene is now triggered 6. Translation of the mRNA produces a protein that performs the  function originally called for by the signal.


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