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Home , Anabolism, Endergonic reaction, Protein metabolism

Chapter 3 Chapter Outline

• Metabolism • Metabolic Reactions and • Reaction Rates • Oxidation • Stages of Glucose Oxidation: , the Krebs Cycle, and Oxidative • Energy Storage and Use: Metabolism of , Fats, and • Metabolism • Metabolism is the sum of all chemical reactions occurring in a cell • Energy metabolism is the set of reactions that involve energy exchange. 3.1 Types of Metabolic Reactions • o Small are used to make large ones for example the use amino acids to synthesize o Consume energy • is the opposite of anabolism • Chemical Reactions o Reactants (or substrates)  Products A + B  C + D o Many reactions can be both forward  and reverse ← o (Hydro= ; lysis=splitting) breaks a larger to smaller ones. A-B + H2O  A-OH + H-B o Condensation (synthesis) is the reverse of hydrolysis. o Phosphorylation - the addition of a group: A + Pi  A-P o Dephosphorylation - the removal of a phosphate group o Oxidation—removal of electrons (or H) o C6H12O6 + 6 O2  6 CO2 + 6 H2O + 36ATP HA-BH  A=B + 2 H o + - o H2  2 H + 2 e o Reduction—addition of electrons (or H) 3.2 Metabolic Reactions and Energy • Energy is the ability to do • Potential energy is stored energy. • Kinetic energy is the energy of movement • Energy Changes in Reactions o (a) is the energy releasing reaction that goes forward spontaneously. o Endergonic reaction (b) is the energy absorbing reaction. • The Law of Mass Action o An increase in the concentration of reactions relative to products tends to push a reaction forward. A + B  C + D o An increase in the concentration of products relative to the reactants tends to push a reaction in reverse. • The is the difference between the energy of the transition state and the energy of either reactants or products.

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3.3 Reaction Rates • The reaction rate is a measure of how fast products are made per unit time. • Factors Affecting Reaction Rates o Reactant and concentration . ↑ reactant concentration → faster forward reaction rate . ↑ product concentration → slower forward reaction rate

o Environmental . : ↑ temperature till certain degree→ faster reaction rate . pH: optimal at different body location • The Role of Enzymes in Chemical Reactions o Enzymes . Are proteins that function as catalysts for reactions in biological systems. They speed up reaction. . Are identified by the suffix –ase. . Are not changed nor consumed in the reaction. . Can be denatured by extreme temperature or pH.

o The Mechanism of Enzyme Action: . Lock and key model . Induced-fit model . Both and product can bind at the to allow reverse reaction occur (Figure 3.7) . Enzymes speed up chemical reactions by decreasing activation energy for a specific

o Enzyme Properties . Saturation: With the increase of substrate concentration, the enzymes reach maximum velocity (Vmax) • Cofactors are I ons or non-protein molecules required by an enzyme for the enzyme to be active o Organic molecules: o Trace metals—Mg, Ca, Zn, Fe • Coenzyme are organic molecules derived from vitamins that transfer chemical groups during chemical reactions Coenzyme Chemical Transferred + NADH (B3) H + FAD riboflavin (B12) H pantothenic (B5) acid acetyl • Factors Affecting Rates of Enzyme-catalyzed Reactions o Enzyme’s catalytic rate o Concentrations of enzyme and substrate o Affinity of enzyme for substrate o Other factors: temperature and pH • Enzyme’s Catalytic Rate o Amount of product produced per unit time o Some enzymes are inherently faster than others o Concentration of Enzyme and Substrate 2

o Affinity o Optimal pH o Optimal Temperature • Daily : Vegetables and Gas o Humans do not possess the α-GAL enzyme to break raffinose family oligosaccharides (RFOs) in vegetables such as beans. o RFOs are fermented by which do possess the α-GAL enzyme and make gases such as CO2, CH4 and or H2 3.4 ATP: The Medium of Energy Exchange • ATP is a which serves as an energy storage molecule. • ATP hydrolysis: ATP + H2O  ADP + Pi + energy • ATP synthesis: ADP + Pi + energy  ATP + H2O • Universal Energy Molecule ATP • ATP in Coupled Reactions 3.5 Glucose Oxidation: The Central Reaction of Energy Metabolism • Glucose catabolism = The central reaction of energy metabolism 3.6 Stages and Locations of Complete Glucose Oxidation • : Glycolysis Glucose + 2 NAD+ + 2 ADP+ 2 Pi → 2 pyruvate + 2 NADH + 2 H+ + 2 ATP • Mitochondria o + . Acetyl CoA formation 2 pyruvate + 2 CoA+ 2 NAD +2 H2O → 2 acetyl CoA + 2 NADH + 2 + H + 2 CO2 + + . Krebs cycle: acetyl CoA + 3 NAD + FAD +ADP+ Pi+ 3 H2O→ 2 CO2 + 3 NADH +3H +FADH2 + ATP + CoA o Inner mitochondrial membrane (Cristae) . Oxidative phosphorylation + + 10 NADH + 10 H + 2 FADH2 + 28 ADP + 28 Pi + 6 O2 → 10 DAD +2 FAD + 12 H2O + 28 ATP . Use of movement of electrons down the (ETC) to synthesize ATP . Oxygen is the final electron acceptor . Produce most ATPs

• Mechanisms of ATP Synthesis o Substrate-level phosphorylation: phosphate group is transferred from a substrate to ADP to form ATP . X-P + ADP  X + ATP . Glycolysis . Krebs cycle

o Oxidative phosphorylation . Transport H atoms or electrons along the electron transport chain and to capture energy by chemiosmosis coupling . ADP + Pi  ATP

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• Incomplete Glucose Oxidation o or occurs when oxygen availability is low or cells like red blood cells do not have mitochondria + o Glycolysis can continue only if NADH is oxidized to form NAD • Aerobic conditions Glucose + 6O2 + 38ADP + 38Pi  6CO2 + 6H2O + 38ATP • Anaerobic conditions Glucose + 2ADP + 2Pi  2 + 2ATP 3.7 Energy Storage and Use: Metabolism of Carbohydrates, Fats and Proteins (Figure 3.24) • The metabolism of carbohydrates, fats and proteins is connected. A human body can also extract energy from fat and protein when glucose is in short of supply.When the supply of glucose is plentiful, the body can go through the reverse reaction to synthesize fat and protein and store glucose as glycogen. • Glycogen Metabolism o and o is the production of new from , lactate and amino acids. Occurs in , small extent in kidneys • Fat Metabolism o and o : fatty acids are made to acetyl CoA • o Proteins are broken down to amino acids by Hereditary Metabolic Disorder http://www.merckmanuals.com/home/sec23/ch282/ch282a.html 

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