Metabolic Pathways revisited Overview of energy unit Importance of ATP Regulation of metabolic pathways 1 Students will understand how energy is transformed from chemical or solar energy into the universal power source of cells ATP Focus Cells use ATP to do work Regulation of metabolic pathways 2 General principles Organic molecules in a cell began with the fixation of carbon from CO2 during photosynthesis Water CO2 sunlight time 3 Overview of respiration and photosynthesis PHOTOSYNTHESIS GLUCOSE RESPIRATION CO2 H2O temporary storage CO2 H2O Catabolic pathways Anabolic pathways ATP Simple monomers and organic molecules Macromolecules 4 The same molecule can serve many different functions in the cell Amino acids serve as building blocks for more complex molecules proteins heme synthesis pathway melanin synthesis pathway Nucleic acids can serve as building blocks for RNA and DNA energy sources RNA A and G become signals GTP is the G of G proteins and G protein coupled receptors Lipids can serve as energy sources and signals building blocks steroid hormones 5 ATP is a common currency for most cellular reactions Three negative charges repel each other Makes the molecule unstable Unstable high energy 6 ATP hydrolysis is exergonic ATP G 30 5 kJ mol H2O ADP Pi Energy release 7 ATP and ADP are used for cellular work ADP can be hydrolyzed as well H2O ATP H2O ADP AMP Pi Pi Cellular processes use up ATP and ADP if ATP is unavailable 8 ATP and ADP are used for cellular work Pi ATP H2O Pi ADP H2O AMP AMP turns into cyclic AMP The reverse reactions reconstituting ATP require a very steep input of energy what kind of reactions are they Respiration and photosynthesis ensure the cell has a steady supply of ATP at all times Both processes produce ATP directly Photosynthesis also stores quick fuel for respiration in the form of glucose 9 Metabolic pathways including those that create ATP are ALWAYS highly regulated by the cell Mechanisms of regulation 1 2 Control whether enzymes are present to begin with transcription gene regulation Control of existing enzymes feedback inhibition phosphorylation other post translational modifications degradation of enzyme Also triggered through phosphorylation 10 Feedback Inhibition allosteric Metabolic pathway synthesis of enz 1 enz 2 enz 3 When we want synthesis on high concentrations of substrate low concentrations of product When we want it off high concentrations of final product 11 There are thousands of any given molecule enzyme at any time not just one Relative concentrations determine rate of metabolic pathway regulated by feedback inhibition symbol for inhibition enz 1 enz 2 enz 3 rate of synthesis is rate of synthesis is synthesis is High little inhibition Low some inhibition Halted mostly inhibited 12 To access transfer the energy in ATP one of the phosphate groups is attached to something else If it s attached to a reactant it gives the reactant more free energy G If it s attached to a macromolecule it will change the 3D shape of that molecule Post translational modifications of proteins change protein function 13 Phosphorylation can act as an onoff switch Pi from ATP hydrolysis can also be attached to proteins This always causes a conformational change that This is also called Phosphorylation Inactive enzyme Active enzyme Active enzyme P Inactive enzyme P Active binds ion P Inactive pump Pushes ion across P 14 Phosphorylation can act as an onoff switch Inactive enzyme kinase phosphetase kinase Active enzyme Active enzyme P Inactive enzyme phosphetase P A whole new sub category of enzymes add phosphate groups to things usually proteins Protein x Phosphetase remove phosphate groups from things usually proteins 15 Example MAPK phosphorylation MAPK MAPK MAPK kinase ATP Serine threonine tyrosine histidine ADP 16 ATP is a multi purpose signal Block active site deactivation Increase efficiency active enzyme Dimerization with partner Cause this protein s destruction 17 Phosphorylation is only one of many posttranslational modifications that change protein function Next slide an image from the literature of regulatory sites on p53 a tumor suppressor protein Source Gu Zhu 2012 Int J Biol 8 5 672 684 p53 is regulated by many different posttranslational modifications 19 P53 phosphorylation sites have different functional consequences Phosphorylation is Example Inhibition through phosphorylation glycogen synthase glucose monomers glycogen fibers 21 Hey what is glycogen and how is it linked A carbohydrate peptide bonds B protein ester linkages C carbohydrate glycosidic linkages D protein peptide bonds E phospholipids not covalently linked 22 Inhibition through phosphorylation glycogen synthase kinase GSK 3 P glycogen synthase glycogen synthase glycogen synthase glycogen synthesis active glucose monomers glycogen fibers 23 Inhibition through phosphorylation glycogen synthase kinase GSK 3 P glycogen synthase glycogen synthesis active inhibited glucose monomers X glycogen fibers 24 Often there are cascades of phosphorylation P yet another Kinase Protein Kinase B AKT AKT activated by phosphorylation P glycogen synthase kinase GSK 3 GSK 3 inactivated by phosphorylation glycogen synthase glycogen synthesis active glucose monomers glycogen fibers 25 AKT has multiple sites for phosphorylation that have different effects P P Phosphorylation of Thr450 is necessary for proper folding Without this modification the protein is degraded Nature Structural Biology 9 940 944 2002 AKT has multiple sites for phosphorylation that have different effects GSK 3 active site now open P P P P inactive AKT active AKT Phosphorylating this Thr Thr309 gives the Thr a negative charge which attracts the blue loop to 3 basic residues His196 Arg274 and Lys298 Nature Structural Biology 9 940 944 2002 AKT has multiple sites for phosphorylation that have different effects P P P P P P P phosphorylated GSK 3 AKT AKT AKT P P time active AKT Phosphorylating this residue makes the enzyme 10x more active Nature Structural Biology 9 940 944 2002 Other ways to inhibit an enzyme not generally used by body though often a mechanism of action of drugs reversible competitive inhibition another molecule competing for active site can be overcome by adding more substrate other covalent modifications chemicals or toxins bind to enzyme and render it inoperative permanently 29 You should be able to Explain how chemicals and molecules in a cell can be used for multiple functions and give examples Explain ATP s