Respiration Flashcards
Cellular respiration
The process by which chemical energy in organic molecules (e.g. carbohydrates, fats and proteins) is released by oxidation. The energy released is then used to generate ATP.
Properties of ATP
• ATP is soluble and can transport chemical energy to energy-consuming
processes anywhere within the cell.
• Hydrolysis of ATP requires the addition of water and releases energy.
➢ ATP is converted to ADP and inorganic phosphate (Pi).
• Phosphorylation of ADP can form ATP. This reaction releases water and is known
as condensation. The enzyme that catalyses the reaction is called ATP synthase.
➢ ADP is phosphorylated with inorganic phosphate (Pi) to form ATP.
Properties of ATP
• ATP is soluble and can transport chemical energy to energy-consuming
processes anywhere within the cell.
• Hydrolysis of ATP requires the addition of water and releases energy.
➢ ATP is converted to ADP and inorganic phosphate (Pi).
• Phosphorylation of ADP can form ATP. This reaction releases water and is known
as condensation. The enzyme that catalyses the reaction is called ATP synthase.
➢ ADP is phosphorylated with inorganic phosphate (Pi) to form ATP.
Stages of aerobic respiration, location, reactants, products
Glycolysis - cytoplasm - Glucose oxidised - 2 molecules of pruvate, net 2 ATP, 2 reduced NAD - does not require O2
Link reaction - mitochondrial matrix of eukaryotic cells - pryuvate oxidised - 2 acetyl-CoA, 2 CO2, 2 reduced NAD - occurs in the presence of O2 -
Krebs cycle - mitochondrial matrix of eukaryotic cells - further oxidation of acetyl-CoA in a series of reactions - 6 reduced NAD, 2 reduced FAD, 4 CO2, 2 ATP - occurs in the presence of O2
Oxidative phosphorylation - Inner mitochondrial membrane of eukaryotes - electrons released from oxidation in first 4 stages - electron transport chain releases large amounts of ATP
Glycolysis
• ATP is soluble and can transport chemical energy to energy-consuming
processes anywhere within the cell.
• Hydrolysis of ATP requires the addition of water and releases energy.
➢ ATP is converted to ADP and inorganic phosphate (Pi).
• Phosphorylation of ADP can form ATP. This reaction releases water and is known
as condensation. The enzyme that catalyses the reaction is called ATP synthase.
➢ ADP is phosphorylated with inorganic phosphate (Pi) to form ATP.
Glycolysis: Energy-investment phase
1) Activation of glucose occurs to make it
more chemically reactive
➢ Phosphorylation of glucose using
ATP
➢ Glucose → Glucose-6-phosphate
➢ Catalysed by hexokinase
2) Isomerisation of glucose-6-phosphate
to fructose-6-phosphate
3) Phosphorylation of fructose-6-phosphate using ATP
➢ Fructose-6-phosphate → Fructose-1,6-bisphosphate
➢ Catalysed byphosphofructokinase
4) Cleavage of fructose-1,6-bisphosphate
(6C) into 2 triose phosphates (3C),
which are dihydroxyacetone phosphate
and glyceraldehyde-3-phosphate
(GALP / GP / G3P)
5) Isomerisation of dihydroxyacetone
phosphate into glyceraldehyde-3-
phosphate
➢ At the end of step 5, 2 molecules
of glyceraldehyde-3-phosphate
(GALP) have been formed from a
single glucose molecule.
Glycolysis: Energy payoff phase
Energy in the form of ATP is produced via substrate level phosphorylation (4 ATP per
glucose molecule) in this phase.
Steps 6-10:
• Subsequent conversion of each GALP
to pyruvate via multiple steps:
➢ Generates 2 ATP via
substrate-level phosphorylation
➢ Releases protons (H+) and
electrons (e-) via dehydrogenation which are transferred to 1 oxidised NAD
(NAD+) to form 1 reduced NAD
(NADH + H+)
Glycolysis: Energy payoff phase
Energy in the form of ATP is produced via substrate level phosphorylation (4 ATP per
glucose molecule) in this phase.
Steps 6-10:
• Subsequent conversion of each GALP
to pyruvate via multiple steps:
➢ Generates 2 ATP via
substrate-level phosphorylation
➢ Releases protons (H+) and
electrons (e-) via dehydrogenation which are transferred to 1 oxidised NAD
(NAD+) to form 1 reduced NAD
(NADH + H+)
Substrate level phosphorylation
• Mode of ATP synthesis whereby an enzyme transfers a phosphate group from
a substrate molecule to ADP.
• Occurs in cytoplasm (during glycolysis) and in the mitochondrial matrix (during
Krebs cycle in which ATP is generated).
Link reaction
in the presence of O2, pryuvate passes into the mitochondrion through the outer and inner mitochondrial membranes via active transport. In the mitochondrial matrix, pryuvate is converted to acetyl-CoA by oxidative decarboxylation
3 reactions of link reaction
- Decarboxylation
- carboxyl group of pryuvate is removed and carbon dioxide is released - Oxidation
- remaining 2C molecule undergoes oxidation via dehydrogenation by transferring protons and electrons to oxidised NAD, therefore converting it to reduced NAD - Addition of Coenzyme A
- Coenzyme A is attached to acetate to form acetyl-CoA
Krebs cycle
- acetyl CoA (2C) is attached to oxaloacetate (4C). the resulting 6C compound, citrate, is then gradually re-coverted back to oxaloacetate.
- cycle runs twice per glucose molecule
decarboxylation occurs:
- from isocitrate to alpha-ketoglutarate
- from alpha-ketoglutarate to succinyl-CoA
dehydrogenation occurs:
- from isocitrate to alpha-ketoglutarate
- from alpha-ketoglutarate to succinyl-CoA
- from succinate to fumarate
- from malate to oxaloacetate
substrate level phosphorylation occurs:
- from succinyl CoA to Succinate
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Oxidative phosphorylation
is the mechanism of ATP synthesis where electrons (released from the first three stages) are transferred from coenzymes, reduced NAD and reduced FAD, to the electron transport chain
- Electron transport chain
- Chemiosmosis
Oxidative phosphorylation: electron transport chain (ETC)
organisation of ETC:
- composed of a collection of electron carriers embedded in the inner mitochondrial membrane
- extensively folded inner mitochondrial membrane (cristae) increases surface area to provide space for thousands of copies of the chain in each reaction
- the electron carriers are numbered I through IV in decreasing levels of free energy
processes:
1. reduced NAD and reduced FAD transfer high energy protons and electrons to the ETC for the synthesis of ATP
2. Electrons are passed along the ETC from one electron carrier to the next, each with an energy level lower than the one preceding it.
3. Electron carriers alternate between reduced and oxidised states as they accept and donate electrons
4. the last electron carrier passes the electrons to oxygen which functions as the final proton acceptor to form water, catalysed by cytochrome oxidase
1/2 O2 + 2H+ +2e- -> H2O
5. Oxidised NAD and oxidised FAD are regenerated in the process
Oxidative phosphorylation: chemiosmosis
Coupling of ETC to ATP synthesis
- as the electrons are passed from one electron carrier to the next, energy released is used to pump protons from the matrix of mitochondrion into the intermembrane space.
- High concentration of H+ in the intermembrane space -> steep electrochemical proton gradient -> proton motive force
- this impermeable nature of hte inner mitochondrial membrane to H+ alllows this gradient to be established
- Stalked particles each containing ATP synthase are embedded on inner mitochondrial membrane. H+ diffused through them, down the electrochemical proton gradient, back into the matrix
- this provides enough energy to synthesise ATP by the phosphorylation of ADP with inorganic phosphate (Pi)
- electrons from each reduced NAD yield 2.5 ATP
- electrons from each reduced FAD yield 1.5 ATP
