BIOENERGY

• Metabolism


  Sum total of all chemical reactions in a living organism
• Catabolism


  All metabolic reactions in which large biochemical molecules are broken down to smaller ones
• Anabolism


  All metabolic reactions in which small biochemical molecules are joined to form larger ones
• Metabolic Pathway


  Series of consecutive biochemical reactions used to convert a starting material into an end product
• Types of metabolic pathways

  • Linear
  • Cyclic
• Protein synthesis


  Synthesis of a protein from amino acids
• Polysaccharide hydrolysis


  Hydrolysis of a polysaccharide to monosaccharides
• Prokaryotic cell


  Single compartment organism, no nucleus, found only in bacteria
• Eukaryotic cell


  Multi-compartment cell, DNA present in membrane-enclosed nucleus, ~1000 times larger than bacterial cells
• Mitochondria


  Organelle responsible for generating most of the cell's energy
• AMP


  Structural component of RNA
• ADP and ATP


  Key components of metabolic pathways, phosphate groups connected by strained bonds
• ATP function


  Source of phosphate group and source of energy for cellular reactions
• Flavin adenine dinucleotide (FAD)


  Coenzyme required in redox reactions, flavin subunit is the active form
• FAD redox reaction


  Conversion of alkane to alkene, FAD is oxidized form, FADH2 is reduced form
• NAD+


  Coenzyme, NADH is the reduced form
• NAD+ redox reaction


  Oxidation of a secondary alcohol to a ketone
• Coenzyme A


  Derivative of vitamin B, active form is the sulfhydryl group (-SH) in the ethanethiol subunit, acetyl-CoA is the acetylated form
• Classification of metabolic intermediate compounds

  • Based on their functions
• High-energy phosphate compounds


  Contain at least one reactive, strained bond, have greater free energy of hydrolysis than normal compounds
• Free energies of hydrolysis of common phosphate-containing metabolic compounds
• Biochemical energy production


  1. Digestion

  2. Acetyl group formation

  3. Citric acid cycle

  4. Electron transport chain and oxidative phosphorylation
• Digestion


  Begins in mouth, continues in stomach, completed in small intestine, results in small molecules that can cross intestinal membrane
• Acetyl group formation


  Small molecules from digestion are further oxidized, end product is acetyl CoA
• Citric acid cycle


  Takes place in mitochondria, acetyl group is oxidized to produce CO2 and energy, most energy trapped in NADH and FADH2
• Citric acid cycle


  A series of biochemical reactions in which the acetyl portion of acetyl CoA is oxidized to carbon dioxide and the reduced coenzymes FADH2 and NADH are produced
• Tricarboxylic acid cycle (TCA) or Krebs cycle


  Also known as the citric acid cycle
• Regulation of the citric acid cycle

  • The rate at which the citric acid cycle operates is controlled by ATP and NADH levels
  • When ATP supply is high, ATP inhibits citrate synthase (Step 1)
  • When ATP levels are low, ADP activates citrate synthase
  • NADH acts as an inhibitor and ADP as an activator for isocitrate dehydrogenase
• Overall ETC reaction


  2 H+ + 2e- + 1/2 O2 → H2O + energy
• Electron transport chain


  • The enzymes and electron carriers are located along the inner mitochondrial membrane
  • Organized into four distinct protein complexes and two mobile carriers
• Four protein complexes in the ETC

  • Complex 1: NADH-coenzyme Q reductase
  • Complex II: Succinate-coenzyme Q reductase
  • Complex III: Coenzyme Q - cytochrome C reductase
  • Complex IV: Cytochrome C oxidase
• Complex I: NADH-Coenzyme Q Reductase


  • NADH from citric acid cycle is the source of electrons
  • Contains >40 subunits including FMN and iron-sulfur protein clusters
  • Facilitates transfer of electrons from NADH to coenzyme Q
• Complex II: Succinate-coenzyme Q Reductase


  • Smaller than complex I, contains 4 subunits including iron-sulfur protein clusters
  • Converts succinate to fumarate, generating FADH2
  • CoQ is the final recipient of the electrons from FADH2
• Complex III: Coenzyme Q – Cytochrome c Reductase


  • Contains 11 different subunits
  • Several iron-sulfur proteins and cytochromes are electron carriers
  • Cytochrome is a heme iron protein in which reversible oxidation of an iron atom occurs
• Complex IV: Cytochrome c Oxidase


  • Contains 13 subunits including two cytochromes
  • Electrons flow from cyt c to cyt a to cyt a3
  • In the final stage, electrons from cyt a3 and H+ combine with O2 to form water
• 95% of the oxygen used by cells serves as the final electron acceptor for the ETC
• Oxidative phosphorylation


  • Process by which ATP is synthesized from ADP and Pi using the energy released in the electron transport chain
  • Coupled reactions - energy released by one reaction is used in the other reaction
• Coupling of ATP synthesis with the ETC

  • Related to the movement of protons (H+ ions) across the inner mitochondrial membrane
  • Complexes I, III and IV serve as "proton pumps" transferring protons from the matrix side to the intermembrane space
• For every two electrons passed through ETC, four protons cross the inner mitochondrial membrane through complex I, four through complex III and two more though complex IV
• ATP synthesis


  The high concentration of protons passing through ATP synthase becomes the basis for the ATP synthesis