Energy in ATP
Respiration is a process where the organic molecules such as glucose, fatty acids, glycerol and amino acids are broken down by a series of enzymatic chemical reactions to produce energy in ATP form. It is called catabolism. Catabolism involves three stages which shown in Fig.1 :
- Conversion of building blocks into acetyl-CoA
- Oxidation of acetyl-CoA
The main fuels is glucose. Glucose is broken down in four stages:
- Link reaction
- Krebs cycle
- Oxidative phosphorylation
- Lysis/breakdown of glucose.
- Multiple enzymatic steps.
- Break 6C glucose to 2 molecules of 3C pyruvates.
- Produces 4 ATP
- Uses 2ATP
- Net gain: 2ATP
- In aerobic metabolism (presence of oxygen)
- Pyruvate loses carbon dioxide.
- The remaining two carbon atoms become linked to coenzyme A as an acetyl group to form acetyl-CoA, which then enters the citric acid cycle.
- Called aerobic glycolysis.
- Called anaerobic glycolysis.
- Occur in cytoplasm.
- In muscle, reduction of pyruvate to lactate by lactate dehydrogenase.
- NAD is recycle in glycolysis.
- Allow some ATP produced even the oxygen is not available.
- Lactate is carried through plasma to liver and convert to pyruvate to glucose (gluconeogenesis).
- Pyruvate passes by active transport from cytosol into mitochondrion matrix.
- It is decarboxylated, dehydrogenated and combine with coenzyme A (CoA) to form acetyl CoA.
- Also known as tricarboxylic acid cyle (TCA cyle), citric acid cycle.
- Closed pathway of enzyme controlled reactions.
- In a Krebs cycle, 3 NADH, 1 FADH2 and 1 ATP are produced.
|Energy producing reaction||No of ATP produced|
|3 NADH||9 ATP|
Oxidative phosphorylation & electron transport chain
- Oxidative phosphorylation and electron transport chain are the final stage of aerobic respiration.
- It is aerobic pathway and occur in mitochondrion.
- Enzyme : oxidoreductase.
- NADH and FADH2 are passed to electron transport chain.
- Hydrogen ions are removed and split to hydrogen ion (H+) and electron.
- Electron is then transferred to the first series of electron carrier (cytochrome). Hydrogen ion remains in matrix.
- Electron is transferred to oxygen, a hydrogen ion will be drawn and reduce oxygen to water.
- Electron transfer makes energy available which is used to convert ADP + Pi to ATP.
Besides glucose, lipid and protein are also broken down into smaller substances and provide energy. The catabolism pathway of lipid and protein are linked into Krebs cycle.