3.3 Aerobic Respiration Flashcards
What is respiration?
- A catabolic process involving a series of enzyme-catalysed reactions in cells in which energy rich respiratory substrates are broken down to release energy as ATP
Aerobic respiration
Glucose + Oxygen –> Carbon dioxide + Water + Energy
C₆H₁₂O₆ + 6O₂ –> 6CO₂ + 6H₂O + ATP
NAD
Function:
-Hydrogen and electron acceptor molecule
-Acts as a coenzyme by assisting dehydrogenase enzymes by accepting protons and transferring them to other molecules
Structure:
-Two nucleotides both containing ribose sugar
-One nucleotide containing adenine base
-One nucleotide containing nicotinamide ring
Stages of Aerobic Respiration
1) Glycolysis
2) The Link Reaction
3) The Krebs Cycle
4) The Electron Transport Chain (ETC)
Glycolysis
-Means the breaking of sugar
- Takes place in the cytosol of cells (The liquid part surrounding organelles) as glucose is too big to enter mitochondria and enzymes needed are found here
Stages of Glycolysis
1) Activation of glucose (By phosphorylation):
- 2x inorganic phosphate ions from 2 ATP added to glucose (6C)
-Destabilises glucose and makes more reactive
- Forms Glucose diphosphate (6C)
2) Splitting of phosphorylated glucose:
- Glucose diphosphate is unstable and reactive
- It splits to 2x Triose phosphate (3C)
3) Oxidation of Triose Phosphate (TP):
- Each Triose phosphate (3C) loses 2x hydrogen
- 2x Triose phosphate is oxidised to 2x Pyruvate (3C)
-This stage is catalysed by dehydrogenase enzymes and the coenzyme NAD
-NAD is reduced to form NADH/ reduced NAD
4) ATP production (By substrate level phosphorylation):
- 4x ADP are phosphorylated by 2x Pi from Triose Phosphate and 2x Pi from cytosol
- 4x ATP is formed for 2x Pyruvate
The Link Reaction
- Occurs in the matrix of the mitochondria
-Pyruvate is actively transported into mitochondria via carrier proteins and involves the decarboxylation of pyruvate to Acetyl CoA
The Link Reaction stages
- Pyruvate (3C) is oxidised/dehydrogenated, catalysed by dehydrogenase enzymes
- NAD acts as an acceptor and is reduced to NADH
- Pyruvate is also decarboxylated (catalysed by decarboxylase enzymes) to Acetate (2C) and CO₂
-Acetate (2C) combines with Coenzyme A (CoA) to form Acetyl CoA
The Krebs Cycle
- Occurs in the matrix of the mitochondria
- Involves a series of enzyme catalysed reactions
The Krebs Cycle stages
1) Entering the Krebs Cycle:
- The Coenzyme A fragment of Acetyl CoA helps the 2C Acetyl fragment to enter the Krebs Cycle
- The Coenzyme A fragment detaches and is recycled
2) Hydrolysis of Oxaloacetate (4C) to Citrate (6C)
- Oxaloacetate (regenerated during the Krebs Cycle) combines with Acetate (2C) to form Citrate (6C)
- A water molecule is inserted during the bond breaking process
3) Oxidative decarboxylation of Citrate (6C)
- Citrate (6C) is oxidised (catalysed by dehydrogenase enzymes)
- NAD is reduced to NADH
- Citrate also decarboxylated (catalysed by decarboxylase enzymes) and a CO₂ is yielded
- Hydrolysis also occurs at this stage
- α-Ketoglutarate is formed (5C)
4) Oxidative decarboxylation of α-Ketoglutarate (5C)
- α-Ketoglutarate (5C) is oxidised (catalysed by dehydrogenase enzymes)
- NAD is reduced to NADH
- α-Ketoglutarate (5C) is decarboxylated (catalysed by decarboxylase enzymes) to Succinate (4C) and a CO₂ is yielded
5) Substrate level phosphorylation
- A substrate molecule acts as a donor of a phosphate group
- ATP is produced by substrate level phosphorylation
6) Oxidation of Succinate (4C)
- Succinate (4C) is oxidised (catalysed by dehydrogenase enzymes) to Fumarate (4C)
- FAD is reduced to FADH₂
7) Hydrolysis of Fumarate (4C)
- Fumarate (4C) is hydrolysed to Malate (4C)
- High energy bonds are broken and lower energy bonds are formed
8) Oxidation of Malate (4C)
- Malate is oxidised (catalysed by dehydrogenase enzymes) to regenerate Oxaloacetate (4C)
- NAD is reduced to NADH