E 2.1 Investigate the process of respiration What do we mean by respiration? • First, we mean ‘cellular respiration’ (not inand-out lung breathing) • Most microorganisms (any other organisms) oxidise (burn) carbohydrate as their primary source of energy for cells • Carbohydrate catabolism is the breakdown of carbohydrate molecules to produce energy • Glucose is the most common carbohydrate energy source used by cells Terminology • • • • • • • • Biochemists use a lot of jargon We will start using some of this Carbohydrate = CHO Glucose = glc anaerobic = no air aerobic = in presence of air ATP = adenosine triphosphate Electron transport chain = ETC Energy from glucose • To produce energy from glucose, microorganisms use two general processes: – cellular respiration – Fermentation • Both start with the same first step (glycolysis) but then follow different subsequent pathways Cellular respiration • Respiration is defined as an ATP generating process in which molecules are oxidised and the final electron acceptor is generally an inorganic molecule • An essential feature is the operation of an electron transport chain • There are two types of respiration: – aerobic (uses oxygen) – Anaerobic (no oxygen) Aerobic respiration • In the TCA (tricarboxylic acid) or Krebs or citric acid cycle, large amounts of potential chemical energy that have been stored in acetyl CoA are released slowly, stepwise. • In this cycle, a series of oxidations and reductions transfer that potential energy in the form of electrons to electron carrier coenzymes (chiefly NAD+) Anaerobic respiration • In anaerobic respiration, the final electron acceptor is an inorganic substance other then oxygen • Some bacteria can use a nitrate ion as the final acceptor (reduced to a nitrite ion) • Other bacteria use sulfate (to form hydrogen sulfide) • And others use carbonate (to form methane) The electron transport chain • The ETC consists of a sequence of carrier molecules that are capable of oxidation and reduction • As electrons are passed through the chain, there occurs a stepwise release of energy which is used to drive the chemiosmotic generation of ATP • The final oxidation is irreversible The overall process of respiration • 1. Glycolysis produces ATP and reduces NAD+ to NADH while oxidising glucose to pyruvic acid. The pyruvic acid is converted to the first reactant in the TCA cycle • 2. The TCA cycle produces ATP and reduces NAD+ (and another electron carrier called FADH2) while giving off CO2. The NADH and FADH2 from both processes carry electrons to the electron transport chain • 3. In the electron transport chain the energy of the electrons is used to produce large amounts of ATP Test your knowledge • SEE: Seeley Stephens Tate animations ‘How glycolysis works’ ‘How the Krebs cycle works’ and ‘How the electron transport chain works’ and take the quizzes • Make sure that you are able to describe the process of respiration and its energy ‘budgeting’