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
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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’