Respiration is the process by which cells use oxygen to break down glucose and other food molecules, and use the energy from these reactions to produce ATP, which cells use as energy currency. It occurs in three main stages - glycolysis, the Krebs cycle in the mitochondria, and oxidative phosphorylation. During these stages, electrons are transferred through electron carriers and coenzymes like NADH and FADH2, building up a proton gradient across the mitochondrial inner membrane. ATP is then produced as protons flow back through ATP synthase enzymes. The overall process converts glucose and oxygen into carbon dioxide, water, and ATP to power cellular work.

2. What is respiration?
 The process whereby energy stored in complex organic
molecules is used to make ATP. It occurs in living cells.
 ATP is a phosphorylated nucleotide and it is the
universal energy currency.
 Energy is the ability to do work.
 All living things need energy to drive their biological
processes, all reactions that take place within an
organism are known collectively as METABOLISM.
 Anabolic reactions (build up small to large molecules)
 Catabolic reactions (break down large to small)

3. Metabolic processes?
 The ones which require energy are:
 Active Transport – moving ions across a membrane
against a concentration gradient. (Much of an
organisms energy is used for this)
 Secretion – large molecules that need to be exported
by exocytosis.
 Endocytosis – bulk movement of large molecules into
cells.
 Movement
 Replication of DNA.

4. Where does the energy come from?
 Plants, protoctists and some bacteria =
PHOTOAUTOTROPHS.
 They use sunlight energy in photosynthesis to make
large, organic molecules that contain chemical
potential energy. The plants are eaten by consumers,
and the energy can be released in respiration.
 The energy released is used to phosphorylate
ADP, making ATP which contains lots of energy.

5. The role of ATP
 Phosphorylated nucleotide.
 High-energy intermediate compound found in both
prokaryotic and eukaryotic cells.
 Each molecule = adenosine + 3 phosphate groups.
 It can be hydrolysed to ADP + Pi = 30.6Kj energy per
mol.
 So energy can be released in small, manageable
amounts = cells will not be damaged and energy will
not be wasted.
 ATP = UNIVERSAL ENERGY CURRENCY.

6. Stages of respiration
 Glycolysis – happens in the cytoplasm of all cells, it
can take place with or without oxygen. It breaks down
glucose (6C sugar) into 2 x Pyruvate (3C sugar).
 The link reaction – happens in the matrix of
mitochondria, pyruvate is dehydrogenated,
decarboxylated and converted to ACETATE.
 Krebs Cycle – happens in the matrix of mitochondria,
acetate is decarboxylated and dehydrogenated.
 Oxidative phosphorylation – takes place on cristae
of mitochondria. ADP is phosphorylated to ATP.

7. Coenzymes
 During the first 3 stages of respiration, substrate
molecules are OXIDISED (H atoms removed).
 These reactions are catalysed by DEHYDROGENASE
enzymes, but the enzymes are not very good at
catalysing oxidation or reduction reactions.
 So COENZYMES are needed to help them (e.g NAD)
 They carry the H atoms to the inner membranes of
mitochondria (for oxidative phosphorylation later).

8. NAD
 Organic molecule.
 Helps dehydrogenase carry out oxidation reactions.
 Made of two linked nucleotides
 When it accepts 2 H atoms, it is reduced, when it loses
them, it is oxidised.
 Operates in the first 3 stages of respiration.

9. Coenzyme A
 Its function is to carry ETHANOATE, made from
pyruvate during the link reaction, onto the Krebs
cycle.
 Simple really!

10. GLYCOLYSIS – Stage 1
 Phosphorylation
 1 ATP molecule is HYDROLYSED and the Pi group released
is attached to glucose at carbon 6, so it is now FRUCTOSE
6-phosphate.
 Another ATP is hydrolysed and the Pi is attached to
fructose 6-phosphate at carbon 1, so it is now called
fructose 1,6-BISPHOSPHATE.
 The energy released activates the hexose sugars and
prevents it from being transported out of the cell. It is now
known as HEXOSE 1,6-bisphosphate.
 Note that 2 ATP molecules have been used in this stage.

11. Glycolysis – Stage 2
 Splitting of hexose 1,6-bisphosphate
 Each molecules of hexose 1,6-bisphosphate is split into
2 x TRIOSE PHOSPHATE.
 It is a 3 carbon sugar with a phosphate group attached.

12. Glycolysis – Stage 3
 Oxidation of triose phosphate
 Anaerobic process – each triose phosphate molecule is
oxidised.
 This involves dehydrogenase enzymes, aided by NAD.
 NAD = hydrogen acceptor, so becomes rNAD.
 At this stage, 2 molecules of NAD are reduced per
molecule of glucose.
 2 x ATP molecules are also formed = SUBSTRATE
LEVEL PHOSPHORYLATION.

13. Glycolysis – Stage 4
 Conversion of triose phosphate to pyruvate
 4 enzyme-catalysed reactions convert each triose
phosphate molecule to a molecule of pyruvate (3C).
 Another 2 molecules of ATP are produced.

14. Products of glycolysis?
 2 x ATP
 2 x rNAD
 2 x pyruvate

16. Mitochondria
 The Matrix
 Site of link reaction and Krebs cycle.
 Contains catalytic enzymes, NAD, oxaloacetate.
 The outer membrane
 Contains proteins (forms channels or carriers)
 The Inner Membrane
 Folded into many cristae (large SA)
 Many electron carriers and ATP synthase enzymes
embedded in it.

17. The Link Reaction
 Converts pyruvate to acetate. NAD is reduced.
 2pyruvate+2NAD+2CoA2CO₂+2rNAD+2acetylCoA
 NAD becomes reduced, CoA accepts acetate to be
acetyl CoA, CoA carries acetate to Krebs cycle.
 No ATP produced
 However each rNAD will take a pair of H atoms to
inner mitochondrial matrix to make ATP during
oxidative phosphorylation.

18. The Krebs Cycle
 Also takes place in mitochondrial matrix.
1. Acetate of offloaded from CoA and joins oxaloacetate to
form citrate.
2. Citrate is decarboxylated and dehydrogenated to form a
5C compound. 1 x rNAD is reduced.
3. The 5C compound is decarboxylated and dehydrogenated
to form a 4C compound + 1 x rNAD.
4. The 4C compound is changed into another 4C compound
= x ATP produced = SUBSTRATE LEVEL
PHOSPHORYLATION
5. “ “ = x rFAD
6. The 3rd 4C compound is dehydrogenated and regenerates
oxaloacetate + 1 x rNAD produced

19. KC Continued…
 1 turn of the cycle = 1 x acetate so…
 2 turns of the cycle = 1 x glucose
 Yay…

20. Chemiosmosis
 As electrons flow along the electron transport chain,
energy is released and used to pump protons across
the intermembrane space.
 This builds up a proton gradient (also a pH gradient)
and an electrochemical gradient.
 So potential energy builds up in the intermembrane
space.
 H ions cannot diffuse through the lipid part of the
inner membrane but can diffuse through ion channels.
 The flow of H ions is known as chemiosmosis.

21. Oxidative Phosphorylation
 Formation of ATP by the addition of PI to ADP in the
presence of oxygen:
 AS protons flow through an ATP Synthase enzyme,
they drive the rotational part of the enzyme which
joins ADP and Pi to form ATP.
 The electrons are passed from the last electron carrier
in the chain to molecular oxygen, which is the final
electron acceptor!
 H ions also join so that oxygen is reduced to water.

22.  And that, my friends, is RESPIRATION!
 All you have to do know is learn it all (mwahahaha)