LS2 Lec 3 Membrane (4 Slides)

LS2 Lec 3 Membrane (4 Slides) - Levels of Organizations...

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Unformatted text preview: Levels of Organizations Atoms Life Sciences 2 Molecules Macromolecules Membrane Physiology & Signaling Chapter 6 & 7 Dr. Joseph Esdin • Self-organization Constant temp, constant • Self-Regulation pH • Self-Support and Movement • Self-Replication Organelle Cell cytosol has more water than interstitial fl uid Cells & Their Environment • Cytosol is known as intracellular Cytosol fluid • Interstitial fluid is known as extracellular fluid Cells & Their Environment Blood • • • • • Concentration of energy-rich molecules Concentration of O2 and CO2 Concentration of waste products pH more H+ equals more acidic, gets rid of it Concentration of water, salt, and other electrolytes • Volume and Pressure • Temperature Interstitial fluid 1 Membrane Composition and Structure Variation of Cells • Cell membranes are bilayered, dynamic – Perform vital physiological roles – Form boundaries between cells and their environments – Regulate movement of molecules into and out of cells neuron • Lipids, proteins, and carbohydrates in various combinations make these tasks possible muscle cell epithelial Membrane Composition and Structure Plasma Membrane Extracellular fluid Glycoprotein Glycolipid Choline Phosphate - Head (polar, hydrophilic) Glycerol Fatty acid Tails (nonpolar, hydrophobic) Cholesterol Various Channel membrane Intracellular fluid Phospholipid proteins 2 Membrane Composition and Structure • All biological membranes contain proteins • Many membrane proteins have hydrophilic and hydrophobic regions • The association of protein molecules with lipid molecules is not covalent Membrane Composition and Structure Integral proteins Peripheral proteins Membrane Composition and Structure • Integral membrane proteins have hydrophobic regions of amino acids that penetrate or entirely cross the phospholipid bilayer • Peripheral membrane proteins are found on one side of the membrane Membrane Composition and Structure • Some proteins are restricted in movement because they are anchored to components of the cytoskeleton or are trapped within regions of lipid rafts • This causes an unequal distribution of proteins, allowing for specialization of certain regions of the cell membrane 3 Membrane Composition and Structure • Some cells have carbohydrates associated with their external surfaces • Carbohydrate-bound lipid is called glycolipid • Most of the carbohydrate in the membrane is covalently bonded to proteins, forming glycoproteins Cell-To-Cell junctions • Allow the interaction in between neighboring cells • Three different types – Desmosomes – Tight junctions – Gap junctions Membrane Composition and Structure • Two types of proteins may be in the membrane – Integral proteins – Peripheral proteins • These proteins function in – Junctions – Channels and pumps – Chemical signals DesmosomesSkin Plasma membrane Extracellular space lumen 1 2 3 4 Cells blood 4 lots of transport- digestive system kidneys Tight Junctions Plasma membrane Tight junctions 1 Extracellular space 2 3 4 5 Cells Tight Junction Tight Junctions • Pushes cells very close to each other to minimize space in between them • Prevents paracellular pathways Plasma membrane Tight junctions 1 Extracellular space 2 3 4 5 Cells Gap Junctions Tight junction Plasma membrane Extracellular space 1 2 3 4 Cells 5 Gap Junctions Membrane of cell 2 Membrane of cell 1 connexon Gap junctions Longitudinal section Large molecules can not pass through Small ions and molecules pass through Passive Processes of Membrane Transport • Biological membranes are selectively permeable. They allow some substances to pass, while others are restricted • Some substances can move by simple diffusion through the phospholipid bilayer 6 connexin make 1 c onnexon. Diffusion • Molecules or ions move from region of high concentration to a region of low concentration • The difference in concentration is known as concentration gradient Diffusion • Diffusion can occur through – Lipid bilayer – Through ion channels that are embedded within the membrane and highly specific for a particular ion 6 Diffusion Through a Membrane Chemical Terminology Permeable membrane • Sugar = solute • Water = solvent Water • Solution = water + sugar (sugar dissolved in water) Sugar Diffusion Through a Membrane High [C] (1) (2) (3) Diffusion Low [C] • Movement of molecules occur in both side however, the net movement is to one side only 7 Diffusion Passive Processes of Membrane Transport If substance can permeate the membrane If the membrane is impermeable to a substance Passive Processes of Membrane Transport Passive Processes of Membrane Transport • Small molecules can move across the lipid bilayer by simple diffusion • The more lipid-soluble the molecule, the more rapidly it diffuses • An exception to this is water, which can pass through the lipid bilayer more readily than its lipid solubility would predict • Osmosis is the diffusion of water across membranes • Osmosis is a passive process • Water will diffuse from a region of its higher concentration (low concentration of solutes) to a region of its lower concentration (higher concentration of solutes) 8 Osmosis Osmosis Membrane is permeable to water only Higher water low solute concentration Lower water high solute concentration What Would Happen If You Place a Cell in a Solution? Water concentration is equal Steady state (equilibrium) It Depends on the Solution • Isotonic solution: Same amount of solute compared to the intracellular • Hypertonic solution: higher solute (low water) compared to the intracellular fluid • Hypotonic solution: lower solute (high water) compared to the intracellular fluid 9 Isotonic Solution Hypertonic Solution cell is shrunk b/c water left Hypotonic Passive Processes of Membrane Transport • Polar and charged substances do not diffuse across lipid bilayers • One way for these important raw materials to enter cells is through the proteins embedded within the membrane • These proteins are known as channels cell may burst oxygen and CO2 move through the lipid portion of the membrane Oxygen moves in CO2 moves 10 Diffusion Ion Channels • Diffusion can occur through – Lipid bilayer – Through ion channels that are embedded within the membrane and highly specific for a particular ion Subunit Channel pore Ion Channels Ion Channels Voltage gated • The amino acid sequence of the protein of the channel spans the membrane more than one time (transmembrane) Stretch gated 11 ion through ion channels is not diffusion according to the textbook Ion Channels Phosphorylation gated Ligand gated Mediated Transport • Two types – Facilitated diffusion – Active transport Mediated Transport phosphate added to protein • Used to transport molecules larger than ions • Special proteins embedded within the membrane known as transporters or carriers • The molecule to be transported binds to the pore of the transporter • Slower than ion channels • Highly specific Facilitated Diffusion • Proceeds from high concentration to low concentration • Can become saturated 12 Facilitated Diffusion Outside Glucose Mediated Transport • Two types – Facilitated diffusion – Active transport Inside bind to protein Active Transport • Active transport requires the expenditure of energy • Ions or molecules are moved across the membrane against the concentration gradient Active Transport • Involves three different types: – Uniport transporters move a single type of solute (Ca2+, H+) – Symport transporters move two solutes in the same direction (Na+/Glu) – Antiport transporters move two solutes in opposite directions, one into the cell, and the other out of the cell (Na+/K+ pump) 13 Active Transport Primary Active Transport • Movement of molecules from low concentration to high concentration • It requires expenditure of energy • Two types – Primary active transport – Secondary active transport Primary Active Transport: Na/K Pump Out In per ATP 3 Na out 2 K in • Requires ATP molecules • Also known as pumps • Only cations such as Na+, K+, Ca2+, & H+ pass through primary active transport Secondary Active Transport • Does not use ATP • Use the chemical gradient of one ion to move another ion • Na-glucose cotransporter uses the energy of the Na to move the glucose against its concentration gradient 14 Secondary Active Transport: Na-Glucose Cotransporter Endocytosis • Brings macromolecules, large particles, small molecules into the cell • Two types: – Phagocytosis – Pinocytosis solid liquid • The plasma membrane invaginates toward the cell interior while surrounding the materials Exocytosis • Exocytosis is the process by which materials packaged in vesicles are secreted from the cell • The vesicle membranes fuse with the plasma membrane and release vesicle contents (wastes, enzymes, hormones, neurotransmitter) into the suuroundings Endocytosis & Exocytosis Plasma membrane 15 Extracellular Receptor: GProtein • Messenger binds to receptor and activates it • Receptor activates an integral protein called G-protein • Inactive G-protein is bound to GDP • When GDP unbinds • GTP binds to alpha subunit • Alpha subunit translocates Extracellular Receptor: GProtein • Alpha subunit of G-protein activates adenelyl cyclase (AC) • AC converts ATP to cAMP • cAMP activates protein kinase A (PKA) • PKA phosphorylate other proteins in the cell bringing a cellular response Extracellular Receptor: G-Protein Extracellular Receptor: GProtein Plasma Membrane G protein intermediary Molecules in second messenger system # !" ! Extracellular chemical messenger bound to membrane receptor 1 (Binding of extracellular A TP messenger to receptor activates a G protein, the a subunit of which shuttles to and activates adenylyl cyclase ) Adenylyl cyclase (Converts) Cyclic AMP Activated adenylyl cyclase Cyclic AMP Protein k inase A 6 Brings about cellular response (10) P 10 Amplification 5,00 ATP ADP (Phosphorylation i nduces protein to change shape) Altered protein shape and function Amplification (50) 4 (Phosphorylates ) 5 = phosphate Second messenger 3 (Activates) Particular protein P 1 ! 2 Receptor Total number of molecules Activated protein k inase 1,000 Phosphorylated (activated) protein (e.g., an enzyme) Amplification Products of activated enzyme Amplification (100) (100) 100,000 10,000,000 16 ...
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This note was uploaded on 10/26/2011 for the course LS 2 taught by Professor Pires during the Spring '08 term at UCLA.

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