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Chapter 25: Metabolism & Nutrition – Biol 2402 Dr. Welch

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Chapter 25: Metabolism & Nutrition – Biol 2402 Dr. Welch CHAPTER 25: METABOLISM & NUTRITION – BIOL 2402 DR. WELCH Review the following from Chapter 2. Chemical Reactions List 4 types of reactions. Describe the events that occur in metabolism (include AKAs and energy placement). A. A chemical reaction depends on energy as well as particle concentration, speed, and orientation. Products vs. reactants B. Four Basic types of chemical reactions 1. Synthesis (A+B --> AB + H2O) dehydration; anabolism; endergonic 2. Decomposition (AB + H2O --> A+B) hydrolysis; catabolism; exergonic 40% energy released used for cellular function the rest used for _________________. 3. Redox (AB + CD --> AD + BC) Review electron transfer and agents. 4. Reversible (A + B <==> AB) These may require special conditions (heat or light); Metabolism 5. All anabolic and catabolic reactions (as well as enzymatic activity) in the body are collectively defined as METABOLISM . Energy – Review: energy coupling; energy from an exergonic rxn used to drive an endergonic rxn. A. ENERGY is the capacity to do work; stored as ATP in the body = “energy currency” ADP + P + E ATP. B. Potential (Ep) vs. Kinetic (Ek) (stability & tendency) C. Mechanical (movement) vs. Chemical (store with in bonds) D. Activation energy (Ea) - the minimum energy that reactants must have to start a reaction 1. Molecules are constantly in motion 2. With sufficient Ek, molecules can overcome the natural tendency to repel and come together 3. ENZYMES - protein catalysts used to decrease to Ea and accelerate reactions exponentially a. Rise in temperature (fever) increases collision potential b. Enzymatic activity is directly proportional to concentration of reactants and environmental circumstance I. 3 fates of molecules absorbed in GI A. Used to supply energy – Give examples. B. Serve as building blocks C. Stored for future use II. Mechanism of ATP Generation A. Substrate-level Phosphorylation – in cytosol ATP ADP + high energy P B. Oxidative Phosphorylation – occurs in inner membrane of mitochondria; electrons removed from organic compounds (food) to ETC to O2 C. Photophosphorylation – only in chlorophyll containing plants or bacteria with light-absorbing pigment. CH2O Metabolism Glucose is preferred by body cells and is the primary fuel! Polysaccharides & disaccharides hydrolyzed into monosaccharides (Glucose~80%, Galactose & Fructose). Fructose converted to glucose thru intestinal epithelial cells & hepatocytes; Hepatocytes covert almost all galactose to glucose. What is the normal blood glucose level? I. Fate of Glucose – . ATP Production – immediate energy. AA Synthesis – build proteins (ribosomes) . Glycogen Synthesis – muscles & hepatocytes = glycogenesis for storage in liver & skeletal muscle. Triglyceride Synthesis – transforms excess into glycerol & FA = lipogenesis. (adipose) II. Glucose Movement into Cells . Absorbed in GI & kidney tubules via Na+-glucose symporters (2oAT). 1 . Other cells use GluT via facilitated diffusion. Insulin increases GluT4 & increases glucose entry. What 2 structures is glucose entry always “turned on”? III. Glucose Catabolism: C6H12O6 + 6O2 + 36 or 38 ADPs +36 or 38 P 6CO2 + 6H2O + 36 or 38 ATPs GLYCOLYSIS – SPLITTING GLUCOSE Location Reactants Net Product Oxygen Required? Enzymes Cytoplasm/ Cytosol Glucose (6C) 2 pyruvate (3C) No Lactic Acid Phosphofructokinase 2 ATP Yes Acetyl CoA 2 NADH + H+ CONVERTING PYRUVIC ACID ACETYL COA Entry into Pyruvic Acid (X2) Acetyl CoA (X2) Yes Pyruvate Mitochondria CO2 (X2) dehydrogenase (Matrix) NADH + H+ (X2) KREBS CYCLE (CITRIC ACID CYCLE) Mitochondria 2 Acetyl CoA + 2 ATP (X2) Yes (Matrix) Oxaloacetate 2 3 NADH + H+ (X2) Citrate 1 FADH2 (X2) H2O (hydration) 2 CO2 (X2) ELECTRON TRANSPORT CHAIN & CHEMIOSMOSIS Mitochondria (inner 3 Proton Pumps *32-34 ATP * Yes ATP Synthase membrane) O2 6 H2O What is the key regulator of the rate of glycolysis? What is decarboxylation and when does it occur? . Only 4 of 38 ATP ultimately produced by respiration of glucose are derived from substrate-level phosphorylation. The vast majority of the ATP comes from the energy in the electrons carried by NADH (and FADH2). The energy in these electrons is used in the electron transport system to power ATP synthesis. Thousands of copies of the electron transport chain are found in the extensive surface of the cristae, the inner membrane of the mitochondrion. Most components of the chain are proteins that are bound with prosthetic groups that can alternate between reduced and oxidized states as they accept and donate electrons. ELECTRON TRANSPORT CHAIN 1. Electrons drop in free energy as they pass down the electron transport chain. Electrons carried by NADH are transferred to the first molecule in the electron transport chain. a. Need Vitamin B2 (Riboflavin), Iron, Sulfur, Copper. 2. The electrons continue along the chain that includes several cytochrome proteins and one lipid carrier. 3. The electrons carried by FADH2have lower free energy and are added to a later point in the chain. Electrons from NADH or FADH2ultimately pass to oxygen. The electron transport chain generates no ATP directly. A protein complex, ATP synthase, in the cristae actually makes ATP from ADP and Pi. Its function is to break the large free energy drop from food to oxygen into a series of smaller steps that release energy in manageable amounts. The movement of electrons along the electron transport chain does contribute to chemiosmosis and ATP synthesis. ATP uses the energy of an existing proton gradient to power ATP synthesis. This proton gradient develops between the intermembrane space and the matrix. The proton gradient is produced by the movement of electrons along the electron transport chain. Several chain molecules can use the exergonic flow of electrons to pump H+ from the matrix to the intermembrane space. 2 . This concentration of H+ is the proton-motive force. The ATP synthase molecules are the only place that will allow H+ to diffuse back to the matrix. This exergonic flow of H+ is used by the enzyme to generate ATP. This coupling of the redox reactions of the electron transport chain to ATP synthesis is called chemiosmosis. Chemiosmosis is an energy-coupling mechanism that uses energy stored in the form of an H+ gradient across a membrane to drive cellular work. In the mitochondrion, chemiosmosis generates ATP. Complete oxidation of glucose releases 686 kcal per mole. Formation of each ATP requires at least 7.3 kcal/mole. Efficiency of respiration is 7.3 kcal/mole x 38 ATP/glucose/686 kcal/mole glucose = 40%. The other approximately 60% is lost as heat. Cellular respiration is remarkably efficient in energy conversion. IV. Glucose Anabolism A. Glucose Storage – Glyconeogenesis; carried out by beta cells of pancreas (insulin); need hexokinase Where is glycogen stored? B. Glycogenolysis – glucagon via alpha cells (pancreas) & epinephrine (adrenal medulla) Liver can but not skeletal muscle. Lactic Acid converted to glucose on liver. C. Glucogeogenesis – glucose from lipids & proteins; simulated by cortisol, glucagon (pancreas) & thyroid. 3 .
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