Harvesting Energy

• Anaerobic respiration


  • Form of cellular respiration in some prokaryotes, a molecule other than oxygen is used in the ATP-producing process
• Autotrophs

  Harvest sunlight and convert radiant energy into chemical energy
• Cellular respiration


  Collection of metabolic reactions that breaks down food molecules to produce energy in the form of ATP
• Redox reactions

  Electrons release energy as they pass from a donor molecule to an acceptor molecule, this energy is available for cellular work such as ATP synthesis
• Electron Transport

  ATP is generated by the transfer of electrons from one energy level to another
• Glucose breakdown occurs in 4 stages: Glycolysis in the cytosol, Pyruvate oxidation, The Kreb’s cycle, Electron transport chain and Chemiosmosis for ATP production
• The most common electron carrier is the coenzyme nicotinamide adenine dinucleotide (NAD+)
• Aerobic respiration


  • Form of cellular respiration in eukaryotes and many prokaryotes, oxygen is a reactant in the ATP producing process
• The goal of respiration is to produce ATP
• Heterotrophs


  Live off the energy produced by autotrophs, extract energy from food via digestion and catabolism
• In cellular respiration, dehydrogenases transfer two electrons and one proton to NAD+, resulting in its complete reduction to NADH
• In redox reactions, molecules that accept electrons may also combine with protons (H+), as oxygen does when it is reduced to form water
• Dehydrogenase enzymes facilitate transfer of electrons from a fuel molecule to an electron carrier
• Glucose breakdown occurs in 4 stages
• Electron transport chain and Chemiosmosis

  1. High-energy electrons are delivered to oxygen by a sequence of electron carriers in the electron transport chain

  2. Free energy released by electron flow generates an H+ gradient by chemiosmosis

  3. ATP synthase uses the H+ gradient as the energy source to make ATP
• ATP is synthesized by the enzyme ATP synthase
• Pyruvate oxidation

  1. Enzymes convert the 3-carbon pyruvate into a 2-carbon acetyl group, which enters the citric acid cycle and is completely oxidized to carbon dioxide

  2. Some ATP is synthesized during the citric acid cycle
• 4 ATP are produced by substrate-level phosphorylation in glycolysis, resulting in a net gain of 2 ATP
• Glucose undergoes various reactions in glycolysis including phosphorylation, isomerization, hydrolysis, and dehydrogenation
• There are 2 mechanisms for ATP synthesis: Substrate-level phosphorylation and Oxidative phosphorylation
• ATP


  Cells use ATP to drive endergonic reactions
• The energy for ATP synthesis is derived from the proton gradient formed during the oxidation of glucose
• Breakdown of glucose locations

  • GLYCOLYSIS - CYTOSOL
  • PYRUVATE OXIDATION – MITOCHONDRIAL MATRIX
  • KREB’s CYCLE – MITOCHONDRIAL MATRIX
  • ELECTRON TRANSPORT CHAIN AND ATP SYNTHASE ENZYME – INNER MITOCHONDRIAL MEMBRANE
• Oxidation of glucose

  1. Stage one - Glycolysis

  2. Stage two - Pyruvate oxidation

  3. Stage three - The Kreb’s cycle

  4. Stage four - Electron transport chain and Chemiosmosis (ATP production)
• Kreb’s cycle

  Enzymes break a 6-carbon molecule of glucose into two 3-carbon molecules of pyruvate
• The electron carrier NAD+ is reduced to NADH during glycolysis
• The initial steps of glycolysis require energy - 2 ATP are hydrolyzed
• The free energy of two pyruvate and acetyl-CoA molecules is expressed relative to glucose = 0 kcal/mol
• Stage One of cellular respiration involves glycolysis and stage two involves pyruvate oxidation
• Glycolysis


  Various steps involving different enzymes and reactions
• Pyruvate oxidation occurs in the mitochondria in eukaryotes and in the cytosol in prokaryotes
• There is no ATP made by substrate-level phosphorylation in pyruvate oxidation
• For each 3-carbon pyruvate molecule: 1 CO2, 1 NADH, 1 acetyl-CoA which consists of 2 carbons from pyruvate attached to coenzyme A
• Pyruvate Oxidation

  Removal of CO2 from pyruvate and oxidation of the remaining 2-carbon fragment to an acetyl group carried by acetyl-CoA to the citric acid cycle
• Stage Three of cellular respiration is the Krebs Cycle/Citric Acid Cycle where carbon products of pyruvate oxidation are oxidized to CO2
• Pyruvate oxidation does not occur in the absence of oxygen
• All available electrons are transferred to 3 NAD+ (NADH) and 1 FA in the citric acid cycle
• Stage two

  The Kreb’s cycle
• Each turn of the citric acid cycle produces one ATP by substrate-level phosphorylation
• All available electrons are transferred to 3 NAD+ (NADH) and 1 FAD (FADH2)