Metabolism: catabolism, anabolism • Metabolism- the processes by which cells synthesize biomolecules and generate energy • Catabolism: the process of breaking down larger molecules to extract energy and create reaction substrates. • Anabolism: the process of synthesizing larger molecules for maintenance and new cell generation.
Bioenergetics: ATP • Cells require energy for synthesis, transport, motility, signaling • Energy in cells is transferred largely through ATP (adenosine triphosphate).
Phosphate bond energy Free energy change of reaction ATP is regenerated from ADP when phosphate bonds in other compounds undergo hydrolysis in metabolism or in respiration.
NAD(P)+/NAD(P)H • Nicotinamide adenine dinucleotide • Nicotinamide adenine dinucleotide phospate • Electron donor/receptor for oxidation-reduction reactions • Provides reducing power (hydrogen atoms) for biosynthetic processes • Provides electrons for ATP formation in respiration
Oxidative Phosphorylation • The process by which ATP is formed as a result of the transfer of electrons from NADH or FADH2 to O2 by a series of electron carriers. • Occurs via the electron transport chain (proton gradient). • The major source of ATP for aerobic organisms.
Electron Transport Chain • Composed of two coupled functions • Transfer of electrons from NADH or FADH2 • Use of protons to phosphorylate ADP to ATP
Electron Transport Chain http://www.sp.uconn.edu/~terry/images/anim/ATPmito.html
ATP Generation http://www.sp.uconn.edu/~terry/images/anim/ATPmito.html
Aerobic CatabolismGlycolysis/EMPGlucose pyruvateTCA Cycle/Krebs/Citric Acidpyruvate CO2 + NADHElectron Transport ChainO2H2O H+ ADP ATPNADH NAD gradient…….…………..
Glucose Metabolism • Three major pathways: hexose monophosphate (HMP, also called pentose phosphate), Entner-Doudoroff: (ED),and Embden-Meyerhof-Parnas (EMP, also called glycolysis) • Primary pathway is EMP, an anaerobic pathway that terminates with the production of pyruvate
Net Reaction • For each glucose molecule, two molecules of ATP are regenerated and 2 molecules of pyruvate are produced.
Utilization of pyruvate • Aerobic- pyruvate enters TCA cycle producing CO2 and NADH. • Anaerobic- pyruvate is converted to ethanol, lactic acid, acetone, butanol and/or acetic acid (original definition of fermentation)
TCA Cycle • Called the tricarboxylic acid (TCA) cycle, Krebs cycle, or citric acid cycle • Pyruvate undergoes oxidative decarboxylation with coenzyme A (CoA) to form acetyl-CoA, the immediate precursor for the TCA cycle
TCA Cycle Highlights • Two carbon atoms enter cycle • Four pairs of hydrogen atoms leave the cycle in four oxidative reactions • One high energy phosphate bond is formed (GTP) • Two water molecules are consumed • NADH formed is used as reducing power to generate ATP in electron transport chain
Net Reaction • GTP is used as a phosphoryl donor in protein synthesis and signal transduction processes, or is easily interchangeable with ATP
Production of Biosynthetic Precursors by the TCA Cycle TCA cycle inter-mediates can be funneled off for biosynthesis
Replenishing Intermediates • These intermediates are replaced by anaplerotic reactions (Greek “to fill up”) • Cells can also “fix” CO2 to replace intermediates (heterotropic CO2 fixation). Growth rate can actually be limited by CO2 availability.
Anaerobic Alternatives • Anaerobic respiration can occur by using nitrate as a terminal electron acceptor in the electron transport chain • Many cell can also generate energy without the electron transport chain, but with a lower efficiency.
Alcohol and Lactate Formation No net oxidation or reduction since electron transport chain is not available to produce NAD+ required in TCA cycle
Pentose Phosphate Pathway Generates NADPH (reducing power for for biosynthesis) and 5 carbon sugars (make up ATP, RNA, DNA, others)
Pathways • Many pathways have been elucidated. We have discussed a few of the more common.
Glycolysis Movies(193101, 193201, 193301)TCE/Citric Acid Cycle Movies(193501, 193601)