Week 3 Notes
Week 3 Notes BIOB 260 - 00
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This 5 page Class Notes was uploaded by Ashley Alexander on Wednesday September 23, 2015. The Class Notes belongs to BIOB 260 - 00 at University of Montana taught by Scott Samuels (P), Mark Lindsay Grimes in Fall 2015. Since its upload, it has received 30 views. For similar materials see Cellular and Molecular Biology in Biological Sciences at University of Montana.
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Date Created: 09/23/15
Cell Molec 914 Membranes Energy 0 Kinetic Energy I Energy you can interact with especially movement 0 Potential energy I Stored energy aka enthalpy Essential concepts 0 Noncovalent interactions provide energy for I Three dimensional selfconstruction of membranes WATER 6 Hl H Lewis structure of H20 Molecular geometry of H20 Lipids cause water molecules to be more ordered this decreases entropy and makes free energy more positive therefore this is a more energetically unfavorable situation for hydrophobic molecules such as lipids to be exposed to water directly I like to envision water molecules as monkeys swinging through trees They can maintain their kinetic energy by swinging off of each other and other polar molecules by way of polar regions branches When water encounters a hydrophobic molecule it s like encountering a tree with no branches and the water molecule or monkey has to find a new path in order to keep its momentum Thus its much easier if you can put all of the branchless trees or nonpolar molecules in one place to be avoided 0 Water Tiny sticky tetrahedral forming order around the smoothness 0 Water becomes more ordered around individual nonpolar molecules because water molecules do not interact with them 0 There is NO repulsive force between hydrophobic molecules and water there s just nothing for water to stick to Bilayers form because they are the most energetically favorable state for lipids o Humans can make liposomes a compartment sealed by a phospholipid bilayer Permeability of the Membrane Hydrophobic molecules will pass through a bilayer most easily Small uncharged polar molecules pass through as well Large uncharged polar molecules can pass through Ions rarely pass through without a protein channel or transporter 0 Note in a hypertonic solution it is water that is transferred not ions Membrane Proteins Transmembrane Membrane associated Lipid linked Protein attached 0 Progeria is a disease caused by a point mutation that interferes with a membrane protein that attaches to the nuclear membrane 0 0t helix coil like a present ribbon o 3 sheet like sheet metal 0 Ion channel allows ions through a bilayer Thermodynamics Review Entropy disorder Enthalpy Potential Energetically favorable reaction There still has to be activation energy because of the decrease in entropy Red line is a catalyzed reaction This activation energy can be overcome naturally at high temperatures Enzymes make reactions possible at low temperatures because they bring molecules together decreasing the amount of energy they would need in to come in contact with each other otherwise Other points made in the text The smooth ER synthesizes the building blocks of the phospholipid bilayer Scramblases are enzymes that remove selected phospholipids from one half of the lipid bilayer and insert them into another to maintain homogeneity in the bilayer The Gogli apparatus builds the bilayer making sure the bilayer is correctly assembled Flippases maintain bilayer asymmetry There are different avors of phospholipids and they are specific to the external and internal parts of the bilayer Glycoprotiens proteins with olgiosaccharides bound to them olgiosaccharides are small polysacharrides Proteoglycans one or more long polysaccharide chains that give the cell its slippery surface Cell Molec 916 Membranes Entropy causes lipids to congregate Separation of charges creates membrane potential mV 0 Charges don t like to be separated o The actual number of ions that move is SMALL I 1100000th of the concentration can change the membrane potential by 100mV 0 HIV Vin 39 Vout o Veqk 5 8mVlog1oConcentrationout Concentrationin I 58mV at equilibrium 0 The resting potential depends on how fast ions ow through each channel and the relative conductance o Membrane potential can be set anywhere between 58mV and 5 8mV simply by changing the ratio between Na and K conductance by opening and closing ion specific channels I Channels open by the unscrewing of an 0t helix I Opening of channels is determined by signaling 0 For now just consider them open or closed 0 Changes in membrane potential are used by neurons to transmit information 0 Ion concentrations are not measurably affected during electrical signaling in neurons but the slight changes have large effects The Electrochemical Gradient The chemical and electrical forces across membranes that arise from the asymmetric distribution of charges and ion concentrations 0 Charges don t like to be separated o Mitochondria and Chloroplast use energy from high energy e39 to pump protons H across membranes to make ATP The Nernst Equation 0 V RTzFlnCoCi I RTzF constant in biological situations 58mV 20 C I This derivation is not in the text Cell Molec 918 Electrochemical Gradient Different types of membrane transport Membranes are not very permeable 0 Active transport is often required to move ions against their electrochemical gradient Channels are selective based on size and charge It is easiest to diffuse hydrophobic molecules because water forces it to move toward the hydrophobic fatty acid chains in phospholipids Uniports utilize passive transport single molecules transported at a time Ionophores actively transport ions Active transport ATP driven light driven or coupled transport 0 Coupled transport I Symport 0 Coupling in the same direction I Antiport 0 Coupling in opposite directions Concentration of ions 0 Na High concentration outside of the cell 0 K High concentration inside of the cell 0 Cl39 High concentration outside of the cell 0 Ca2 High concentration outside of the cell I Important for intracellular signaling 0 pH slightly lower inside Glucose Transport 0 Can diffuse passively if concentration is high outside of cell 0 If concentration is low externally glucose Will be coupled in a symport With Na Na K ATPase 9 Very important 0 Sodium is pumped out and K ows passively in forming a charge imbalance across the membrane Cell uses this imbalance like a battery especially in nerve cells 0 Brain uses 20 of all energy just operating this pump 0 Voltage gated Na channels open if the membrane potential depolarizes pas the threshold potential I Pumps become inactivated after use to prevent the signal from moving backward Rising potential open Falling potential inactivated Post hyperpolarization closed Repeat PP Pi o K pumps don t have an inactive state 0 Na pumps do have an inactive state and its important 0 Potential reaches a negative state because K pumps are slower than Na pumps 0 Facilitated diffusion 0 Passive transport by way of a channel opening 0 Molecules still move in the direction of concentration gradient 0 K molecules move out of the cell slowly through FD
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