E 2.1 Investigate the process of respiration

What do we mean by respiration? First, we mean ‘cellular respiration’ (not in- and-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 FADH 2) while giving off CO 2. The NADH and FADH 2 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’