biochemica energy production

• Metabolism


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


  • Provides the source of energy we need for all our activities such as thinking, moving, breathing, walking, talking, etc.
  • Provides energy for many of the cellular processes such as protein synthesis, DNA replication, RNA transcription and transport across the membrane, etc.
• Catabolism


  All metabolic reactions in which large biochemical molecules are broken down to smaller ones
• Energy is usually released in catabolic reactions
• Anabolism


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


  Series of consecutive biochemical reactions used to convert a starting material into an end product

  
• Types of metabolic pathways

  • Linear
  • Cyclic

  
• The major pathways for all forms of life are similar
• Prokaryotic Cell


  • Single compartment organism
  • No nucleus -- found only in bacteria
  • Single circular DNA molecule present near center of the cell called nucleoid
• Eukaryotic Cell


  • Multi-compartment cell
  • DNA is present in the membrane enclosed nucleus
  • Cell is compartmentalized into cellular organelles
  • ~1000 times larger than bacterial cells
• Eukaryotic Cell Organelles and Their Function

  • Nucleus: DNA replication and RNA synthesis
  • Plasma membrane: Cellular boundary
  • Cytoplasm: The water-based material of a eukaryotic cell
  • Mitochondria: Generates most of the energy needed for cell
  • Lysome: Contain hydrolytic enzymes needed for cell rebuilding, repair and degradation
  • Ribosome: Sites for protein synthesis

  
• Mitochondria


  • Outer membrane: Permeable to small molecules: 50% lipid, 50% protein
  • Inner membrane: Highly impermeable to most substances: 20% lipid, 80% protein
  • Inner membrane folded to increase surface area
  • Synthesis of ATP occurs
• Adenosine Phosphates


  • AMP: Monophosphate (one phosphate group)
  • ADP: Diphosphate (Two phosphate groups)
  • ATP: Triphosphate (Three phosphate groups)
  • cAMP: Cyclic monophosphate (Cyclic structure of phosphate)

  
• AMP


  Structural component of RNA
• ADP and ATP


  Key components of metabolic pathways
• Phosphate groups are connected to AMP by strained bonds which require less than normal energy to hydrolyze them
• The net energy produced in these reactions is used for cellular reactions
• ATP


  Functions as both a source of a phosphate group and a source of energy
• Uridine triphosphate (UTP)


  Involved in carbohydrate metabolism
• Guanosine triphosphate (GTP)


  Involved in protein and carbohydrate metabolism
• Cytidine triphosphate (CTP)


  Involved in lipid metabolism

  
• Flavin Adenine Dinucleotide (FAD)


  • A coenzyme required in numerous metabolic redox reactions
  • Flavin subunit is the active form – accepts and donates electrons
  • Ribitol is a reduced form of ribose sugar
• Cellular Reaction involving FAD

  1. Conversion of an alkane to an alkene

  2. FAD is oxidized form

  3. FADH2 is reduced form

  4. In enzyme reactions FAD goes back and forth (equilibrium) from oxidized to reduced form

  
• NADH


  Reduced form of NAD+
• NAD+ structure


  Nicotinamide - ribose – ADP
• NADH structure


  Nicotinamide -- ribose -phosphate --phosphate - ribose – adenine
• Cellular reaction involving NAD+

  Oxidation of a secondary alcohol to give a ketone
• Coenzyme A


  • A derivative of vitamin B
  • Active form is the sulfhydryl group (-SH group) in the ethanethiol subunit of the coenzyme
  • Acetyl-CoA (acetylated)
• Coenzyme A structure


  • 2-Aminoethanethiol - pantothenic acid - phosphorylated ADP
  • 2-Aminoethanethiol - pantothenic acid -phosphate - phosphate phosphorylated ribose - adenine
• High-Energy Phosphate Compounds


  • Several phosphate containing compounds found in metabolic pathways
  • Have greater free energy of hydrolysis than a typical compound
  • Contain at least one reactive bond -- called strained bond
  • Energy to break these bonds is less than a normal bond -- hydrolysis of high energy compounds give more energy than normal compounds
  • More negative the free energy of hydrolysis, greater the bond strain
  • Typically, the free energy release is greater than 6.0 kcal/mole (indicative of bond strain)
  • Strained bonds are represented by sign ~ (squiggle bond)

  
• Energy needed to run human body is obtained from food
• Biochemical Energy Production


  1. Multi-step process that involves several different catabolic pathways

  2. Four general stages: Digestion, Acetyl group formation, Citric acid cycle, Electron transport chain and oxidative phosphorylation

  
• Stage 1: Digestion


  1. Begins in mouth, continues in the stomach, completed in small intestine

  2. Results in small molecules that can cross intestinal membrane into the blood

  3. End Products: Glucose and monosaccharides from carbohydrates, Amino acids from proteins, Fatty acids and glycerol from fats and oils
• Stage 2: Acetyl Group Formation


  1. The small molecules from Stage 1 are further oxidized

  2. End product is acetyl CoA

  3. Reactions occur both in cytosol (glucose metabolism) as well as mitochondria (fatty acid metabolism)

  
• Stage 3: Citric Acid Cycle

  1. Takes place inside the mitochondria

  2. Acetyl group is oxidized to produce CO2 and energy

  3. Most energy is trapped in reduced coenzymes NADH and FADH2

  4. Some energy produced in this stage is lost in the form of heat
• Stage 4: Electron Transport Chain and Oxidative Phosphorylation

  1. Takes place in mitochondria

  2. NADH and FADH2 are oxidized to release H+ and electrons

  3. H+ are transported to the inter-membrane space in mittochondria

  4. Electrons are transferred to O2 and O2 is reduced to H2O

  5. H+ ions reenter the mitochondrial matrix and drive ATP-synthase reaction to produce ATP

  
• ATP is the primary energy carrier in metabolic pathways
• 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
  • Also know as tricarboxylic acid cycle (TCA) or Krebs cycle
  • Citric acid is a tricarboxylic acid – TCA cycle
  • Named after Hans Krebs who elucidated this pathway

  
• Important types of reactions in the citric acid cycle

  • Oxidation of NAD+ and FAD to produce NADH and FADH2
  • Decarboxylation of citric acid to produce carbon dioxide