• Share
  • Email
  • Embed
  • Like
  • Save
  • Private Content
Ch05 lecture
 

Ch05 lecture

on

  • 219 views

 

Statistics

Views

Total Views
219
Views on SlideShare
219
Embed Views
0

Actions

Likes
0
Downloads
11
Comments
0

0 Embeds 0

No embeds

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

    Ch05 lecture Ch05 lecture Presentation Transcript

    • Chapter 5 Cell Membrane Structure and Function Lectures by Gregory Ahearn University of North Florida Copyright © 2009 Pearson Education, Inc..
    • 3.1 What Does The Plasma Membrane Do?  The cell plasma membrane separates the cell contents from the external environment.  The membrane acts as a gatekeeper, regulating the passage of molecules into and out of the cell.  Cell membranes are complex structures that contain many different components. Copyright © 2009 Pearson Education Inc.
    • 3.2 What Is The Structure Of The Plasma Membrane?  Plasma membranes are “fluid mosaics”. • Membranes are composed of a double lipid layer that is highly fluid without breaking. • Proteins are embedded in this double lipid layer and give the membrane its mosaic character. Copyright © 2009 Pearson Education Inc.
    • 3.2 What Is The Structure Of The Plasma Membrane?  The plasma membrane is a fluid mosaic. extracellular fluid (outside) binding site phospholipid bilayer carbohydrate cholesterol phospholipid receptor protein transport protein protein filaments recognition protein cytoplasm (inside) Copyright © 2009 Pearson Education Inc. Fig. 3-1
    • 3.2 What Is The Structure Of The Plasma Membrane?  The phospholipid bilayer is the fluid portion of the membrane.  Phospholipid molecules have a polar head group and a pair of nonpolar tails. CH3 CH2 CH2 CH2 CH2 CH2 CH3 – CH2 O CH2 + H3C N CH2 CH2 O P O CH2 O CH3 CH O HC O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH O H2C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3 tails (hydrophobic) head (hydrophilic) Copyright © 2009 Pearson Education Inc. Fig. 3-2
    • 3.2 What Is The Structure Of The Plasma Membrane?  The head groups are hydrophilic and point toward the aqueous environment on both bilayer sides of the membranes.  The tail groups are hydrophobic and point away from the aqueous environments and toward each other. Copyright © 2009 Pearson Education Inc. extracellular fluid (watery environment) phospholipid hydrophilic heads hydrophobic tails hydrophilic heads cytoplasm (watery environment) Fig. 3-3
    • 3.2 What Is The Structure Of The Plasma Membrane?  A mosaic of proteins is embedded in the membrane. • Some of the membrane proteins are anchored to a network of protein filaments within the cytoplasm. • Other proteins are free to move around in the lipid matrix. • Many proteins have carbohydrate groups that stick outside of the cell. Copyright © 2009 Pearson Education Inc.
    • 3.3 How Does The Plasma Membrane Play Its Gatekeeper Role?  The phospholipid bilayer blocks the passage of most molecules.  The embedded proteins selectively transport, respond to, and recognize molecules.  There are three types of membrane proteins —transport proteins, receptor proteins, and recognition proteins. Copyright © 2009 Pearson Education Inc.
    • 3.3 How Does The Plasma Membrane Play Its Gatekeeper Role?  Membrane proteins • Transport proteins: allow the movement of water-soluble molecules through the plasma membrane by forming channels or by carrying them across • Receptor proteins: possess a binding site on the outer surface for binding specific chemicals that may alter overall cell function • Recognition proteins: with sugar groups attached to the exterior of the cell, are used by the immune system to identify cells as belonging to “self” Copyright © 2009 Pearson Education Inc.
    • 3.3 How Does The Plasma Membrane Play Its Gatekeeper Role? PLAY Animation—Plasma Membrane Structure Copyright © 2009 Pearson Education Inc.
    • 3.4 What Is Diffusion?  Characteristics of molecules in fluids • Concentration: the number of molecules in a given unit of volume • Gradient: a physical difference between two regions of space that causes molecules to move from one region to another Copyright © 2009 Pearson Education Inc.
    • 3.4 What Is Diffusion?  Molecules in fluids move in response to gradients. • Diffusion: the movement of molecules from regions of high molecular concentration to low molecular concentration  A drop of dye in water illustrates diffusion. Copyright © 2009 Pearson Education Inc.
    • 3.4 What Is Diffusion?  Diffusion of a dye in water 1 A drop of dye is placed in water 2 The dye molecules diffuse into the water; the water molecules diffuse into the dye 3 Both dye molecules and water molecules are evenly dispersed drop of dye water molecule Copyright © 2009 Pearson Education Inc. Fig. 3-4
    • 3.4 What Is Diffusion?  Summing up: the principles of diffusion • Diffusion is the movement of molecules down a gradient from high concentration to low concentration. • The greater the concentration gradient, the faster the rate of diffusion. • If no other processes intervene, diffusion will continue until the concentration gradient is eliminated. Copyright © 2009 Pearson Education Inc.
    • 3.5 What Is Osmosis?  Osmosis: the diffusion of water molecules from a high water concentration to a low water concentration across a biological membrane  Pure water has the highest water concentration.  The addition of dissolved solutes to pure water reduces the number of water molecules and thus lowers the water concentration. Copyright © 2009 Pearson Education Inc.
    • 3.5 What Is Osmosis?  Osmotic water flow across a membrane takes place across selectively permeable membranes that allow water to pass, but not certain small impermeable molecules, such as sugars. Copyright © 2009 Pearson Education Inc.
    • 3.5 What Is Osmosis?  A selectively permeable membrane water selectively permeable membrane Water molecule: can fit through the pore sugar Sugar with water molecules clustered around it: cannot fit through the pore Copyright © 2009 Pearson Education Inc. pore Fig. 3-5
    • 3.5 What Is Osmosis?  Example of osmosis: a water-permeable bag that is impermeable to sugar and has sugar inside of it • Water flows into the bag, down a water concentration gradient. • The bag swells and eventually bursts from the additional water. Copyright © 2009 Pearson Education Inc.
    • 3.5 What Is Osmosis?  Osmosis selectively permeable membrane sugar molecule water molecule Copyright © 2009 Pearson Education Inc. Bag bursts Water flows in Fig. 3-6
    • 3.5 What Is Osmosis? PLAY Animation—Osmosis Copyright © 2009 Pearson Education Inc.
    • 3.5 What Is Osmosis?  Summing up: the principles of osmosis • Osmosis is the diffusion of water across a selectively permeable membrane. • Dissolved substances reduce the concentration of water molecules in a solution. • Water moves across a membrane down its concentration gradient from a high concentration of water molecules to a low concentration of water molecules. Copyright © 2009 Pearson Education Inc.
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?  There are two kinds of transport across cell membranes: • Passive transport • Energy-requiring transport Copyright © 2009 Pearson Education Inc.
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane? Copyright © 2009 Pearson Education Inc.
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?  Passive transport: movement of molecules across a membrane, down a concentration gradient, without the use of energy • The phospholipid bilayer and transport proteins regulate which molecules can cross the membrane down concentration gradients. • Membranes are selectively permeable, and only allow some molecules to cross and not others. Copyright © 2009 Pearson Education Inc.
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?  Examples of passive transport • Simple diffusion: the transfer of gases, water, and lipid-soluble substances—such as ethyl alcohol and vitamin A—across the phospholipid bilayer Copyright © 2009 Pearson Education Inc.
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?  Simple diffusion through the phospholipid bilayer (extracellular fluid) lipid-soluble molecules and O2, CO2, and H2O O2 (cytoplasm) (a) Simple diffusion through the phospholipid bilayer Copyright © 2009 Pearson Education Inc. Fig. 3-7a
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?  Examples of passive transport (continued) • Facilitated diffusion: the diffusion of watersoluble molecules through a channel or carrier protein down a concentration gradient • Channel protein: pores in the lipid bilayer through which ions or molecules can diffuse • Carrier protein: membrane protein that grabs a specific molecule on one side of the membrane and carries it to the other side Copyright © 2009 Pearson Education Inc.
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?  Facilitated diffusion via a channel protein Cl– Cl – H2O, ions Proteins form a hydrophilic channel Cl– Cl channel protein (cytoplasm) – Cl– (b) Facilitated diffusion through a channel protein Copyright © 2009 Pearson Education Inc. Fig. 3-7b
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?  Facilitated diffusion via a carrier protein amino acids, sugars, small proteins carrier 1 A carrier protein protein 2 A molecule has a binding site enters the for a molecule binding site (extracellular fluid) 3 The carrier protein changes 4 The carrier protein shape, transporting the resumes its original shape molecule across the membrane (cytoplasm) (c) Facilitated diffusion through a carrier protein Copyright © 2009 Pearson Education Inc. Fig. 3-7c
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane? PLAY Animation—Movement Across a Membrane Copyright © 2009 Pearson Education Inc.
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?  Examples of passive transport (continued) • Water crosses membranes in response to molecular concentration differences on each side of the membrane. Copyright © 2009 Pearson Education Inc.
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?  Isotonic extracellular fluid: the same molecular concentration outside the cell as inside the cell • There is equal movement of water across the cell membrane in each direction under this condition; there is no net water movement. Copyright © 2009 Pearson Education Inc.
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?  Isotonic solution 10 micrometers (a) Isotonic solution has the same salt concentration as the cytoplasm Copyright © 2009 Pearson Education Inc. Equal movement of water into and out of cells Fig. 3-8a
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?  Hypertonic extracellular fluid: the molecular concentration outside the cell is greater than the molecular concentration inside the cell • Net water movement out of the cell; the cell shrinks. Copyright © 2009 Pearson Education Inc.
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?  Hypertonic solution (b) Hypertonic solution has a higher salt concentration than the cytoplasm Copyright © 2009 Pearson Education Inc. Net water movement out of cells; cells shrivel Fig. 3-8b
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?  Hypotonic extracellular fluid: the molecular concentration outside the cell is less than the molecular concentration inside the cell • Net water movement into the cell; the cell swells. Copyright © 2009 Pearson Education Inc.
    • 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?  Hypotonic solution (c) Hypotonic solution has a lower salt concentration than the cytoplasm Copyright © 2009 Pearson Education Inc. Net water movement into cells; cells swell and burst Fig. 3-8c
    • 3.7 How Do Molecules Move Against A Concentration Gradient?  Energy-requiring transport processes • During active transport, the cell uses energy to move substances against a concentration gradient. • Membrane proteins regulate active transport. • Adenosine triphosphate (ATP) donates energy to the active transport processes. Copyright © 2009 Pearson Education Inc.
    • 3.7 How Do Molecules Move Against A Concentration Gradient?  Active transport • One binding site on a protein binds a transported molecule and a second binding site binds ATP. • Energy from ATP moves the other molecule up a concentration gradient. Copyright © 2009 Pearson Education Inc.
    • 3.7 How Do Molecules Move Against A Concentration Gradient?  Active transport (extracellular fluid) 1 The transport protein binds both ATP and CA2+ recognition site ATP binding ATP site Ca2+ Copyright © 2009 Pearson Education Inc. 2 Energy from ATP changes the shape of the transport protein and moves the ion across the membrane 3 The protein releases the ion and the remnants of ATP (ADP and P) and closes ADP ATP P (cytoplasm) Fig. 3-9
    • 3.7 How Do Molecules Move Against A Concentration Gradient?  Endocytosis: moves fluid droplets or large particles across cell membranes • Pinocytosis moves water into a cell. • Phagocytosis moves solid material into a cell. • Receptor-mediated endocytosis transports specific molecules across membranes. Copyright © 2009 Pearson Education Inc.
    • 3.7 How Do Molecules Move Against A Concentration Gradient?  During endocytosis, a portion of the plasma membrane engulfs the extracellular fluid or particle and pinches off into the cytoplasm as a membranous sac, called a vesicle. Copyright © 2009 Pearson Education Inc.
    • 3.7 How Do Molecules Move Against A Concentration Gradient?  Pinocytosis: movement of water into a cell (extracellular fluid) 1 3 2 (cytoplasm) vesicle containing extracellular fluid 1 A dimple forms in the plasma membrane, which 2 deepens and surrounds the extracellular fluid. 3 The membrane encloses the extracellular fluid, forming a vesicle. (a) Pinocytosis Copyright © 2009 Pearson Education Inc. Fig. 3-10a
    • 3.7 How Do Molecules Move Against A Concentration Gradient?  Phagocytosis: movement of solid material into a cell (extracellular fluid) food particle pseudopods 1 (cytoplasm) 2 vesicle containing the particle 3 1 The plasma membrane extends pseudopods toward an extracellular particle (food, for example). 2 The ends of the pseudopods fuse, encircling the particle. 3 A vesicle that contains the engulfed particle is formed. (b) Phagocytosis Copyright © 2009 Pearson Education Inc. Fig. 3-10b
    • 3.7 How Do Molecules Move Against A Concentration Gradient?  Receptor-mediated endocytosis: transports only specific molecules across membranes • The process depends on the many receptor proteins on the outside surface of a cell. • Receptors can be in depressions in the plasma membrane, called coated pits. • The transported molecule binds to receptors in the coated pits, starts the formation of a membrane vesicle that surrounds the bound molecule, and the vesicle enters the cell. Copyright © 2009 Pearson Education Inc.
    • 3.7 How Do Molecules Move Against A Concentration Gradient?  Receptor-mediated endocytosis nutrients (extracellular fluid) receptors 1 coated pit 2 3 (cytoplasm) 4 coated vesicle 1 Receptor proteins for specific molecules or complexes of molecules are localized at coated pit sites. 2 The receptors bind the molecules and the membrane dimples inward. 3 The coated pit region of the membrane encloses the receptor-bound molecules. 4 A vesicle (“coated vesicle”) containing the bound molecules is released into the cytosol. (c) Receptor-mediated endocytosis Copyright © 2009 Pearson Education Inc. Fig. 3-10c
    • 3.7 How Do Molecules Move Against A Concentration Gradient?  Exocytosis: moves material out of the cell, including the waste products of digestion and secreted materials, such as hormones • During exocytosis, a vesicle carrying material to be expelled moves to the cell surface, where the vesicle fuses with the plasma membrane. • Following fusion, the vesicle opens to the extracellular fluid and its contents diffuse out. Copyright © 2009 Pearson Education Inc.
    • 3.7 How Do Molecules Move Against A Concentration Gradient?  Exocytosis (extracellular fluid) plasma membrane secreted material plasma membrane vesicle Material is enclosed in a vesicle that fuses with the plasma membrane, allowing its contents to diffuse out (cytoplasm) 0.2 micrometer Copyright © 2009 Pearson Education Inc. Fig. 3-11
    • 3.7 How Do Molecules Move Against A Concentration Gradient?  Some plasma membranes are surrounded by cell walls. • Cell walls occur around the plasma membranes of plants, fungi, and some bacteria. • Cell walls provide support for the cells, making them capable of resisting gravity and blowing winds. Copyright © 2009 Pearson Education Inc.
    • 3.7 How Do Molecules Move Against A Concentration Gradient?  Some plasma membranes are surrounded by cell walls (continued). • Cell walls are porous to small molecules, which can pass across these barriers to the plasma membrane. • Plasma membranes of these cells regulate the transport of molecules by the same processes as those that occur in other cells without cell walls. Copyright © 2009 Pearson Education Inc.