Soto Biochem 11/10, 11/12
Soto Biochem 11/10, 11/12 CHEM 351
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This 5 page Class Notes was uploaded by Kayli Antos on Sunday November 15, 2015. The Class Notes belongs to CHEM 351 at Towson University taught by Ana Soto in Summer 2015. Since its upload, it has received 10 views. For similar materials see Biochemistry in Chemistry at Towson University.
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Date Created: 11/15/15
Biochem Soto Fall 2015 0 Lipids And Membranes Membrane Transport N N N N N N Aout The first term is the chemical term and the second is the electrical term 2 is the charge F is Faraday s constant 96480 JVmol 1 is the transmembrane potential Both terms will have the units of Jmol AGtranSport 1n Transporters And Channels N N N N Two categories of proteins are involved in movement 69 Transporters bind to a substrate with high specificity and they can be saturated They may also be called carriers 69 Channels allow substrate to move faster than with use of a transporter They also show less specificity and cannot be saturated Their movement is dependent on the electrochemical gradient May also be called pores There are two types of transporters Passive transporters facilitate diffusion down a concentration gradient 69 Active transporters move substrate again a concentration gradient The energy used for this process comes from a chemical reaction or the transport of a different substrate down its concentration gradient The Glucose Transporter N 22 N N Glucose enters red blood cells by facilitated diffusion The glucose transporter in RBCs is GLUTl and is an integral protein Several transmembrane helices lined up produce a membrane channel which is lined with hydrophilic residues These can form hydrogen bonds with glucose to help it move through the channel v Vmax 5 out 0 Ktr Sout Transport of glucose into a cell is reversible As glucose moves into the cell the concentrations inside and outside the cell will approach each other and the rate of glucose moving into and out of the cell will reach equilibrium Similar to the MichaelisMenten Equation Glucose is not taken into the cell against the concentration gradient ChlorideBicarbonate Exchanger N N 22 C02 is released as waste from tissues into the blood It enters RBCs and is then concerted to bicarbonate HCO339 which is more soluble in blood It then reenters the blood plasma and is transported to the lungs When it reaches the lungs it reenters the RBCs and is converted back to C02 which is then exhaled The chloridebicarbonate exchanger mediates the simultaneous movement of HCO339 and Cl39 which move in opposite directions Since both ions have the same charge this exchange is electroneutral Since they move in different directions the exchange is also antiport z Transport can also occur symport and uniport Active Transport z Accumulates the solute past the equilibrium point This is thermodynamically unfavorable so it can only occur With a favorable process z Primary active transport coupled directly to an exergonic chemical reaction like ATP 9 ADP Pi Secondary active transport an unfavorable transport is coupled With a favorable transport of a different solute Which was initially transported against the electrochemical gradient via primary active transport Na K ATPase z Ptype ATPases transport cations and are reversibly phosphorylated by ATP 22 m In animal cells the concentration of Na is higher outside the cell and the concentration of K is higher inside the cell z Na K ATPase maintains these conditions m For each molecule of ATP dephosphorylated to ADP and Pi 2 potassium ions move in and three sodium ions move out 22 The mechanism for Ptype ATPases involved a large conformational change in response to the phosphorylationdephosphorylation of an Asp residue z The movement of sodium and potassium changes the electrical potential of the cell and creates a net separation of charges A transmembrane of 50 to 70 mV is produced Secondary Active Transport E coli produces a proton gradient and a charge across its plasma membrane 22 22 The lactose transporter provides a route of proton reentry and When this occurs lactose is carried into the cell by symport m In intestinal cells glucose can be accumulated by symport With sodium ions Signal Transduction z The conversation of information from outside the cell into a chemical change inside the cell is signal transduction z Are very specific and sensitive and result in an amplification of the signal GProtein Coupled Receptors z There are three components a receptor on the plasma membrane a Gprotein and an effector enzyme z The effector enzyme releases a second messenger to affect other targets iAdrenergic Receptor z Integral proteins With seven transmembrane domains z When epinephrine binds to its receptor a conformational change occurs Which releases the associated Gprotein The 0t subunit of the G protein binds GTP and can activate adenylate cyclase Which catalyzed the synthesis of cAMP from ATP 22 z CAMP allosterically activates protein kinase A which catalyzes the phosphorylation of specific proteins Amplification z One hormone binding to one receptor can release several Gproteins z Each adenylate cyclase that s activated is able to produce several cAMP molecules z Each PKA can catalyze the phosphorylation of multiple molecules Signal Termination z When the concentration of epinephrine decreases the hormone dissociates from the receptor 22 Hydrolysis of GTP by Ga favors the conformation in which Ga binds G57 Here the Gprotein doesn t interact with adenylyl cyclase z cAMP phosphodiesterase catalyzes the hydrolysis of cAMP to AMP z Phosphatases may reverse the phosphorylation of some targets 0 Bioenergetics Autotrophs And Heterotrophs z Living organisms can be classified as autotrophs or heterotrophs Autotrophs build their biomolecules out of atmospheric C02 and energy form sunlight Some produce 02 and H20 as waste products 69 Heterotrophs get their energy and carbon source from the organic products of autotrophs They produce C02 as a waste product Some reactions consume 02 and convert it to H20 z Heterotrophic and autotrophic organisms constantly cycle carbon oxygen and water between them Metabolism z The sum of all chemical reactions that occur in a cell or organism z Proceeds through metabolic pathways which are a series of enzyme catalyzed reactions z Catabolism degradative metabolism where organic nutrient molecules are converted into smaller end products this process releases energy 22 Anabolism building small precursors into larger molecules this process requires energy Metabolic Pathways z Can be linear branched or cyclic Catabolic pathways are usually convergent and anabolic pathways are usually divergent z Anabolic and catabolic pathways are carefully regulated When one is active the other is suppressed Living Organisms Use Energy z Synthetic reactions need energy to occur Cells are very efficient at coupling energy from sunlight or fuels to energy consuming processes necessary to life z Life obeys the laws for thermodynamics Gibbs Free Energy N 22 A measure of the energy that s available from a reaction Areaction Aproducts 39 Areactants AG AH TAS A negative value indicates that the reaction is spontaneous and exergonic A positive value indicates that the reaction is thermodynamically unfavorable and is endergonic Equilibrium N N N N N AG 22 22 22 N N Under standard conditions the force for a system to move to equilibrium is AGO Biochemical standard state AG O occurs at pH 7 and the follow concentrations H20 555 M H 107 M Mg2 103 M m 2 2 H HA AG RTln Ke q Is A Constant Constant for a given reaction The real AG of a reaction of a function of the reactant and product concentrations o CCDd AG AG RT 1n AaBb At equilibrium AG O and AG0 RT 1n Keq I a Irreversible Reactions N N 22 Metabolic reactions that are close to equilibrium will have a small AG value and therefore Will be reversible Enzymes catalyze these steps and can restore equilibrium Reactions that are not close to equilibrium will have a large and negative AG value and Will be irreversible ATP 22 22 22 Heterotrophic cells make ATP from the free energy gained from catabolism of nutrients ATP donates some of its chemical energy to endergonic processes GTP CTP and UTP are energetically equivalent to ATP A TP Hydrolysis N N The hydrolytic cleavage of the end phosphate reduces electrostatic repulsion The lone phosphate Pi is resonance stabilized ADP and Pi are more stable than ATP because they can be more solvated Highly exergonic AG o 305 kJmol but ATP is kinetically stable because the activation energy of hydrolysis is high AGp AG of ATP hydrolysis is much larger than AG 0 and is about 64 kJmol Other Exergonic Reactions N N Products are more stable than in reactants in hydrolysis reactions Where the AG 0 is large and negative z This is because unfavorable chargecharge interactions are removed and products are stabilized by resonance isomerization ionization etc Energy Coupling A highly exergonic and an endergonic reaction can be coupled so the overall sum reaction is exergonic and Will therefore occur spontaneously z AG O values can be added and K eq values are multiplied High Energy Phosphate Compounds Their AG O for hydrolysis is more negative than 25 kJmol Low energy compounds have values less negative than 25 kJmol 22 22 22 Phosphorylated compounds can be synthesized by coupling that With the breakdown of another phosphate compound Which has a more negative free energy ATP Provides Energy By Group Transfers z A single reaction arrow usually represents a twostep process like part of an ATP molecule being covalently attached to the substrate or amino acid of an enzyme Which raises the free energy content z The second step is the displacement of the phosphate A compound gains free energy When the phosphoryl group is transferred to it Some processes don t directly hydrolyze ATP or GTP 22