The Cell Membrane Lecture 10

Outline Review of Cell Components Membrane Composition Lipids Proteins Selective Permeability Transport Proteins Passive Transport Active Transport

Overview of the Cell All organisms are made of cells The cell is the simplest collection of matter that can be alive Cell structure is correlated to cellular function All cells are related by their descent from earlier cells

ENDOPLASMIC RETICULUM (ER) Nuclear envelope Rough ER Smooth ER Figure 6.8a ENDOPLASMIC RETICULUM (ER) Nuclear envelope Rough ER Smooth ER Flagellum NUCLEUS Nucleolus Chromatin Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Figure 6.8 Exploring: Eukaryotic Cells Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome

Nucleus Rough ER Smooth ER Plasma membrane Figure 6.15-1 Figure 6.15 Review: relationships among organelles of the endomembrane system. Plasma membrane

Nucleus Rough ER Smooth ER cis Golgi Plasma membrane trans Golgi Figure 6.15-2 Nucleus Rough ER Smooth ER cis Golgi Figure 6.15 Review: relationships among organelles of the endomembrane system. Plasma membrane trans Golgi

Nucleus Rough ER Smooth ER cis Golgi Plasma membrane trans Golgi Figure 6.15-3 Nucleus Rough ER Smooth ER cis Golgi Figure 6.15 Review: relationships among organelles of the endomembrane system. Plasma membrane trans Golgi

Mitochondria Present in almost all Eukaryotic cells Figure 6.17aa Outer membrane Inner Cristae Matrix 0.1 m Present in almost all Eukaryotic cells RBCs don’t have a nucleus or mitochondria The steps of cellular respiration occur in the mitochondria Glycolysis is in the cytoplasm Citric Acid Cycle & ETC in mitochondria

Free ribosomes in the mitochondrial matrix membrane Figure 6.17a Intermembrane space Outer membrane DNA Inner Free ribosomes in the mitochondrial matrix membrane Cristae Figure 6.17 The mitochondrion, site of cellular respiration. Matrix 0.1 m (a) Diagram and TEM of mitochondrion

Chloroplasts Photosynthesis Contain Chlorophyll – green pigments Figure 6.18aa Stroma Inner and outer membranes Granum 1 m Chloroplasts Photosynthesis Contain Chlorophyll – green pigments A sub category of organelles called Plastids

(a) Diagram and TEM of chloroplast Figure 6.18a Ribosomes Stroma Inner and outer membranes Granum DNA Figure 6.18 The chloroplast, site of photosynthesis. Thylakoid Intermembrane space 1 m (a) Diagram and TEM of chloroplast

Peroxisomes Specialized metabolic compartment Produce Hydrogen Peroxide and convert it to water Perform many different reactions

Cell Membrane - Composition Made up of phospholipids and proteins Amphipathic molecules – have both hydrophobic and hydrophilic regions The membrane is a fluid (moving) structure with proteins embedded in it Mosaic – made of many, varied pieces

Figure 7.5 Fibers of extra- cellular matrix (ECM) Glyco- protein Carbohydrate Glycolipid EXTRACELLULAR SIDE OF MEMBRANE Figure 7.5 Updated model of an animal cell’s plasma membrane (cutaway view). Cholesterol Microfilaments of cytoskeleton Peripheral proteins Integral protein CYTOPLASMIC SIDE OF MEMBRANE 14

Membrane Composition – Phospholipid bilayer Figure 7.2 Hydrophilic head Hydrophobic tail WATER Membrane Composition – Phospholipid bilayer

Membrane Composition Membrane bound proteins have hydrophobic regions Figure 7.3 Phospholipid bilayer Hydrophobic regions of protein Hydrophilic regions of protein Membrane bound proteins have hydrophobic regions

Membrane Composition - Fluidity Figure 7.6 Membrane Composition - Fluidity Phospholipids and some proteins can move Most drift laterally Sometimes (rarely) flip transversly

Membrane Composition - Fluidity Must be fluid to work properly Fluidity depends on temperature Lower temperatures – less fluid Phospholipid types vary Unsaturated fatty acids are more fluid than saturated

Membrane Composition – Fluidity & Cholesterol Cholesterol in animal cell membranes helps maintain fluidity Steroid At warm temps (37 degrees) it slows movement of phospholipids As temp cools, it maintains fluidity by preventing tight packing

Membrane Composition – Fluidity Lipid composition varies from species to species They are adapted to specific environments Some species have the ability to change composition in response to temperature changes where they live.

Membrane Composition - Proteins Lots of different proteins Embedded in the fluid matrix of the lipid bilayer Proteins determine most of the membrane’s specific function

Membrane Composition - Proteins Peripheral proteins – bound to the surface of the membrane Integral proteins – penetrate the hydrophobic core Transmembrane proteins – span the membrane Hydrophobic regions of the protein are usually alpha helices made of nonpolar amino acids

EXTRACELLULAR SIDE N-terminus  helix C-terminus CYTOPLASMIC SIDE Figure 7.9 EXTRACELLULAR SIDE N-terminus  helix C-terminus Figure 7.9 The structure of a transmembrane protein. CYTOPLASMIC SIDE 23

Membrane Composition – Proteins Transport Enzymatic activity Signal transduction Cell-cell recognition Intercellular joining Attachment to the cytoskeleton and Extracellular matrix (ECM)

Membrane Composition – Transport Proteins Figure 7.10a Signaling molecule Receptor Enzymes ATP Signal transduction (a) Transport (b) Enzymatic activity (c) Signal transduction

Selective Permeability Cell must exchange materials with it’s surroundings Controlled by the plasma membrane Nutrients, signaling molecules, Ions in; waste products out. Selectively permeable – the membrane selects what goes in and out, only allowing specific things

Selective Permiability Small, nonpolar molecules can move through Large, polar molecules can’t

Selective Permeability – Transport Proteins Allow hydrophilic substances to cross the membrane Two types: Channel proteins Have a hydrophilic channel that allows polar molecules through Aquaporins are specific for the movement of water Carrier Proteins Bind to molecules and move them across Once the molecule binds, the carrier protein changes shape to move it across They are specific for the substances they move

Selective Permeability – Transport Proteins; Channel proteins

Selective Permeability – Transport Proteins; Channel proteins

Selective Permeability – Passive transport; diffusion Diffusion – the tendency of molecules to spread out evenly into the available space Can be directional At dynamic equilibrium – equal number of molecules moving in both directions

Membrane (cross section) Figure 7.13a Molecules of dye Membrane (cross section) WATER Figure 7.13 The diffusion of solutes across a synthetic membrane. Net diffusion Net diffusion Equilibrium (a) Diffusion of one solute 32

(b) Diffusion of two solutes Figure 7.13b Net diffusion Net diffusion Equilibrium Figure 7.13 The diffusion of solutes across a synthetic membrane. Net diffusion Net diffusion Equilibrium (b) Diffusion of two solutes 33

Selective Permeability – Passive transport; diffusion Substances move down their concentration gradient No work is done Diffusion across a membrane, down the concentration gradient is called passive transport No energy is expended

Selective Permeability – Passive transport; Osmosis The diffusion of water across a selectively permeable membrane Water moves from low solute concentration to higher solute concentration Diffuses until the solute concentration is equal on both sides of the membrane

Lower concentration of solute (sugar) Higher concentration of solute Same concentration of solute Sugar molecule Figure 7.14 H2O Selectively permeable membrane Figure 7.14 Osmosis. Osmosis 36

Selective Permeability – Passive transport; Osmosis Tonicity – the ability of a surrounding solution to cause a cell to gain or lose water Isotonic solution – Solute concentration is the same outside as it is inside the cell No net movement of water across the membrane Hypertonic solution – solute concentration outside is greater than that inside the cell; cell loses water Hypotonic solution – solute concentration outside is less than that inside the cell; cell gains water

Hypotonic solution Isotonic solution Hypertonic solution Figure 7.15 Hypotonic solution Osmosis Isotonic solution Hypertonic solution (a) Animal cell (b) Plant cell H2O Cell wall Lysed Normal Shriveled Turgid (normal) Flaccid Plasmolyzed

Selective Permeability – Passive transport; Osmosis Osmoregulation – organisms need mechanisms for controlling water loss or gain. Various organisms manage osmosis differently based on adaptations to their specific environments

Selective Permeability – Passive transport; Facilitated diffusion Facilitated diffusion – passive transport aided by proteins Transport proteins speed the passive movement of molecules across the membrane Channel proteins Aquaporins – faclilitated diffusion of water Ion channels – gates that open or close in response to a stimulus

Selective Permeability – Active transport Moving solutes against their concentration gradient requires energy Usually provided in the form of ATP Specific proteins are required for specific substances

Facilitated diffusion Figure 7.19 Passive transport Active transport Figure 7.19 Review: passive and active transport. ATP Diffusion Facilitated diffusion 42

Selective Permeability – Active transport; sodium potassium pump ECM – High Sodium, Low potassium Cytoplasm – Low Sodium, High potassium Potassium moves out – Sodium moves in ECM Cytoplasm

EXTRACELLULAR FLUID [Na] high [K] low Na Na [Na] low CYTOPLASM Figure 7.18-1 EXTRACELLULAR FLUID [Na] high [K] low Na Na CYTOPLASM [Na] low Na 1 [K] high Figure 7.18 The sodium-potassium pump: a specific case of active transport. 44

EXTRACELLULAR FLUID [Na] high [K] low Na Na Na Na Na [Na] low Figure 7.18-2 EXTRACELLULAR FLUID [Na] high [K] low Na Na Na Na Na [Na] low ATP CYTOPLASM Na P 1 [K] high 2 ADP Figure 7.18 The sodium-potassium pump: a specific case of active transport. 45

EXTRACELLULAR FLUID [Na] high Na Na [K] low Na Na Na Na Na Figure 7.18-3 EXTRACELLULAR FLUID [Na] high Na Na [K] low Na Na Na Na Na Na ATP CYTOPLASM [Na] low Na P P 1 [K] high 2 ADP 3 Figure 7.18 The sodium-potassium pump: a specific case of active transport. 46

EXTRACELLULAR FLUID [Na] high Na Na [K] low Na Na Na Na Na Figure 7.18-4 EXTRACELLULAR FLUID [Na] high Na Na [K] low Na Na Na Na Na Na CYTOPLASM [Na] low ATP Na P P 1 [K] high 2 ADP 3 K Figure 7.18 The sodium-potassium pump: a specific case of active transport. K P 4 P i 47

EXTRACELLULAR FLUID [Na] high Na Na [K] low Na Na Na Na Na Figure 7.18-5 EXTRACELLULAR FLUID [Na] high Na Na [K] low Na Na Na Na Na Na ATP CYTOPLASM [Na] low Na P P 1 [K] high 2 ADP 3 K Figure 7.18 The sodium-potassium pump: a specific case of active transport. K K K P 5 4 P i 48

EXTRACELLULAR FLUID [Na] high Na Na [K] low Na Na Na Na Na Figure 7.18-6 EXTRACELLULAR FLUID [Na] high Na Na [K] low Na Na Na Na Na Na CYTOPLASM [Na] low ATP Na P P 1 [K] high 2 ADP 3 K Figure 7.18 The sodium-potassium pump: a specific case of active transport. K K K K P 6 K 5 4 P i 49

Selective Permeability - Ion pumps Membrane potential – the voltage difference across a membrane Positive and negative ions are separated on either side of a membrane creating a voltage potential

Selective Permeability - Ion pumps Electrochemical Gradient – drives the diffusion of ions across a membrane Two forces make up the electrochemical gradient Chemical force – the ion’s concentration gradient Electrical force – the effect of the membrane potential on the ion’s movement Electrogenic Pump – a transport protein that generates voltage across a membrane Sodium-potassium pump in animals Proton pump in plants

Selective Permeability - Ion pumps; nerve impulse https://highered.mcgraw- hill.com/sites/0072495855/student_view0/chapter14/anima tion__the_nerve_impulse.html