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• Metabolism


  The sum of all the chemical reactions that take place in an organism
• Catabolism


  The breakdown of large molecules into smaller ones; energy is generally released during catabolism
• Anabolism


  The synthesis of large molecules from smaller ones; energy is generally absorbed during anabolism
• Metabolic pathway


  1. A series of consecutive reactions

  2. Can be linear or cyclic
• Linear pathway


  The series of reactions that generates a final product different from any of the reactants
• Cyclic pathway


  The series of reactions that regenerates the first reaction
• Mitochondria


  • Organelles within the cytoplasm of a cell
  • Contain an outer membrane and an inner membrane with many folds
  • The area between the two membranes is called the intermembrane space
  • The area enclosed by the inner membrane is called the matrix, where energy production occurs
• Digestion


  The catabolism of food, catalyzed by enzymes in the saliva, stomach, and small intestines
• Carbohydrate digestion


  Hydrolyzed into monosaccharides, beginning with amylase enzymes in saliva and continuing in the small intestine
• Protein digestion


  1. Begins when stomach acid denatures the protein and pepsin begins to cleave the large protein backbone into smaller peptides

  2. Then, in the small intestines, trypsin and chymotrypsin cleave the peptides into amino acids
• Triacylglycerol digestion


  Emulsified by bile secreted by the liver, then hydrolyzed by lipase into 3 fatty acids and a glycerol backbone
• Formation of Acetyl CoA


  Monosaccharides, amino acids, and fatty acids are degraded into acetyl groups, which are then bonded to coenzyme A forming acetyl-CoA
• Citric Acid Cycle


  The acetyl CoA is oxidized to CO2, and the cycle also produces energy stored as a nucleoside triphosphate and the reduced coenzymes
• Electron Transport Chain and Oxidative Phosphorylation


  Within the mitochondria, they produce ATP (adenosine 5'-triphosphate)
• ATP


  The primary energy-carrying molecule in the body
• ATP hydrolysis


  Cleaves 1 phosphate group, forming ADP and hydrogen phosphate, releasing 7.3 kcal/mol of energy
• ATP phosphorylation


  The reverse reaction, where a phosphate group is added to ADP, re-forming ATP and requiring 7.3 kcal/mol of energy
• Any process (walking, running, breathing)

  Fueled by the release of energy when ATP is hydrolyzed to ADP
• Energy is released when ATP is hydrolyzed


  Energy is absorbed and stored in ATP when it is synthesized from ADP
• Coupled reactions


  Pairs of reactions that occur together, where the energy released by one reaction is absorbed by the other reaction
• Hydrolysis of ATP


  Provides the energy for the phosphorylation of glucose
• Coenzymes NAD+ and NADH

  NAD+ (nicotinamide adenine dinucleotide) is an oxidizing agent<|>NADH is the reduced form of NAD+, formed by gaining 1 H+ and 2 e-
• Coenzymes acting as oxidizing agents

  1. Gain H+ and e-

  2. Cause oxidation reactions
• Coenzymes acting as reducing agents

  1. Lose H+ and e-

  2. Cause reduction reactions
• When a coenzyme acts as an oxidizing agent


  It gains H+ and e-
• When a coenzyme acts as a reducing agent


  It loses H+ and e-
• Curved arrows


  • Often used to depict reactions that use coenzymes as oxidizing agents
• Coenzymes FAD and FADH2

  FAD (flavin adenine dinucleotide) is an oxidizing agent<|>FADH2 is the reduced form of FAD, formed by gaining 2 H+ and 2 e-
• NADH and FADH2


  • NAD+ and FAD both act as oxidizing agents
  • NADH and FADH2 both act as reducing agents
• Coenzyme A


  Neither an oxidizing nor a reducing agent
• Acetyl CoA formation


  1. Acetyl group reacts with the sulfhydryl end of coenzyme A

  2. Thioester acetyl CoA is formed
• When the thioester bond in acetyl CoA is broken, 7.5 kcal/mol of energy is released
• Citric Acid Cycle


  A cyclic metabolic pathway that begins with the addition of acetyl CoA to a four-carbon substrate. The cycle ends when the same four-carbon substrate is formed as a product 8 steps later.
• Citric Acid Cycle


  • Produces high-energy compounds for ATP synthesis in stage [4] of catabolism
• Overview of the Citric Acid Cycle

  1. Acetyl CoA reacts with a four-carbon substrate to form a six-carbon product (step [1])

  2. 2 C atoms are sequentially removed to form 2 CO2 molecules (steps [3] and [4])

  3. 4 molecules of reduced coenzymes (3 NADH's and 1 FADH2) are formed (steps [3], [4], [6], and [8])

  4. 1 mole of GTP is made in step [5]; GTP is similar to ATP
• Step [1]


  Reacts acetyl CoA with oxaloacetate to form citrate, catalyzed by citrate synthase
• Step [2]


  Isomerizes the 3o alcohol in citrate to the 2o alcohol in isocitrate, catalyzed by aconitase
• Step [3]


  1. Isocitrate loses CO2 in a decarboxylation reaction catalyzed by isocitrate dehydrogenase

  2. The 2o alcohol of isocitrate is oxidized by NAD+ to form the ketone a-ketoglutarate and NADH
• Step [4]


  Releases another CO2 with the oxidation of a-ketoglutarate by NAD+ in the presence of coenzyme A to form succinyl CoA and NADH, catalyzed by a-ketoglutarate dehydrogenase
• Step [5]


  The thioester bond of succinyl CoA is hydrolyzed to form succinate, releasing energy that converts GDP to GTP