Metabolism Cell Metabolism
Energy • Energy is the capacity to do work. A handful of peanuts contains enough energy to boil a quart of water
Energy Forms • Forms of energy: • Potential energy • Kinetic energy Conversion of potential energy to kinetic energy High potential energy Low potential energy Conversion of kinetic energy to potential energy
Cellular Work • Cells use energy for: • Mechanical work • Transport work • Chemical work • Cellular Work • = Metabolism It takes about 10 million ATP molecules per second to power an active muscle cell.
First Law of Thermodynamics • The total amount of energy in the universe remains constant. • Energy can be transformed from one form to another, but it cannot be created or destroyed.
Second Law of Thermodynamics Energy transformations increase entropy (degree of disorder) in a closed system. • No energy conversion is 100 percent efficient. Systems tend to go from states of higher free energy to states of lower free energy.
Exergonic Reactions EnergyReleased High EnergyReactants A + B Low EnergyProducts Energy is released. Products have less energy than starting substance. + C D
Exergonic Example CH2OH O O OH O O H H O O C O EnergyReleased + High EnergyReactants + Low EnergyProducts
Exergonic Energy Diagram high Energycontentofmolecules low Progress of reaction An exergonic reaction: Burning Glucose Activation energy neededto start reaction Glucose + O2 Energy released byburning glucose C O2 + H2O
Endergonic Reactions A B + C D + energy Energy input is required Products store more energy than starting substances. High EnergyProducts Low EnergyReactants
Endergonic Energy Diagram high Energycontentofmolecules low Progress of reaction (b) An endergonic reaction: Photosynthesis Glucose Net energyincrease bysynthesizingglucose Activationenergy fromlight storedby photosynthesis CO2 + H2O
Endergonic Example CH2OH EnergySupplied O O OH + O O H H High EnergyProducts O O C O Low EnergyReactants +
Energy Flow • Energy flows into ecosystems as sunlight. (The sun is life’s primary energy source.) • Producers (autotrophs) trap energy from the sun and convert it into chemical bond energy. • All organisms use the energy stored in the bonds of organic compounds to do work. • LIVING SYSTEMS ARE NOT CLOSED SYSTEMS!
Energy Relationships Chemical reactions either store or release energy. large energy-rich molecules (fats, complex carbohydrates, proteins, nucleic acids) ADP + Pi BIOSYNTHETIC PATHWAYS (ANABOLIC) DEGRADATIVE PATHWAYS (CATABOLIC) simple organic compounds (simple sugars, amino acids, fatty acids, nucleotides) ATP energy-poor products (such as carbon dioxide, water) ENERGY INPUT
The Role of ATP • Cells “earn” ATP in exergonic reactions. • Cells “spend” ATP in endergonic reactions. adenine P P P ribose ATP - adenosine triphosphate
ADP & ATP NH2 NH2 OH OH C C N N C C N N HC HC Adenine Adenine ~ CH CH C C O P O P OH N N N N O O OH H2C H2C Ribose Ribose O O H H H H H H H H P OH OH OH OH OH O OH OH ~ O P O P O O O DiPhosphate ADP High-energyPhosphateBond TriPhosphate ~ ATP
Active Transport High solute concentration Low solute concentration • ATP gives up phosphate to activate protein. • Binding of ATP changes protein shape and affinity for solute. P ATP ADP P P P
Enzyme Action • Enzymes speed up metabolic reactions by lowering activation energy. • Enzymes are substrate specific. • Enzyme activity is regulated by inhibitors. • A cell’s physical and chemical environment effects enzyme activity.
Enzymes are Catalyst • Enzymes speed up metabolic • reactions by lowering activation energy • A catalyst is a chemical agent that changes the rate of a reaction without being consumed by the reaction. • An enzyme is a catalytic protein. • Enzymes regulate the movement of molecules through metabolic pathways.
A B 298oK, no catalyst T, no catalyst high 298oK, inorganic catalyst A + B 298oK, enzyme Energycontentofmolecules C + D low Progress of reaction “Lowering” Activation Energy Fig. 2
Metabolic Pathways D E InitialReactants Intermediates FinalProducts B C A Enzyme 1 Enzyme 2 Enzyme 3 Enzyme 4 Pathway 1 F G Pathway 2 Enzyme 5 Enzyme 6
Enzymes Specificity • b. Enzymes are substrate specific • A substrate is a reactant which binds to an enzyme. • When a substrate or substrates binds to an enzyme, the enzyme catalyzes the conversion of the substrate to the product.
Enzyme Active Sites • The active site of an enzyme is a pocket or groove on the surface of the protein. • • The specificity of an enzyme is due to the fit between the active site and the substrate. • • As the substrate binds, the enzyme changes shape leading to a tighter induced fit.
products induction of fit enzyme-substrate (ES) complex initial binding due to e.g., charge interactions enzyme ES* ES E + P Induced Fit Model substrate Fig. 3 enzyme E + S enzyme unchanged by reaction TRANSITION STATE good orientation but unstable substrate contact with active site
Enzyme-Substrate Interactions Substrate Substrate 1 Substrates enter active site ActiveSite 2 Shape change promotes reaction Enzyme Product released;enzyme ready again
c. Enzyme activity is regulated by inhibitors. • Some molecules inhibit enzymes from catalyzing reactions. • If the inhibitor binds to the same site as the substrate, then it blocks substrate binding via competitive inhibition. • If the inhibitor binds somewhere other than the active site, it blocks substrate binding via noncompetitive inhibition.
End Product Inhibition • Prevents excess accumulation of final product. • Results in alternative pathway and product.
Feedback Inhibition CH3 CH3 CH2 OH H C CH3 H C NH3 H C NH3 H C COOH COOH Feedback InhibitionIsoleucine inhibits enzyme 1 A B C D E 1 E 2 E 3 E 4 E 5 Threonine(substrate) Isoleucine(end product)
Allosteric Regulation vs. Competition Shape of activesite changed Substrate (a) (b) Active Site Enzyme Allosteric Regulatory Molecule Competitive inhibitoroccupies active site Allosteric Site (c)
Effects on Enzyme Action • d. A cell’s physical and chemical • environment effects enzyme activity • The three-dimensional structure of enzymes depend on environmental conditions. • Changes in shape influence the reaction rate. • Some conditions lead to the most active conformation and optimal rate of reaction.
Effect of pH • pH influences shape and reaction rate. • Each enzyme has an optimal pH (usually between pH 6 – 8). • However, digestive enzymes in the stomach are designed to work best at pH 2 while those in the intestine are optimal at pH 9.
Effect of Temperature • As temperature increases, collisions between substrates and active sites occur more frequently. • • At some point, thermal agitation begins to destabilize the protein’s active conformation and the protein denatures. • • Each enzyme has an optimal temperature.
Effect of Cofactors & Coenzymes • Many enzymes require nonprotein cofactors for catalytic activity and include zinc, iron, and copper. • • Organic cofactors, coenzymes, include vitamins or molecules derived from vitamins.
Effect of Substrate Concentration • The rate of product formation increases as the [substrate] increases. • Rate levels when enzyme becomes saturated. • Additional substrate does not not increase reaction rate.
Metabolism The end