Respiration and burning
Respiration is also called as a process to burn nuteirnts in the presence of oxygen to produce energy. But still different from burning. The difference are as follows:
| Respiration | Burning/combustion |
| 1. It occurs in series of chemical steps i.e., stepped process. | It occurs in a single step. |
| 2. It is carried out by enzymes. | It is carried out by heat. |
| 3. It is a biochemical process. | It is a physiochemical process. |
| 4. Energy is liberated as ATP and heat. | Energy is liberated as heat and light. |
| 5. No light energy is produced. | Light energy is produced. |
| 6. It takes place inside a cell. | It does not takes place inside a cell. |
| 7. It occurs at body temperature. | It occurs at high temperature. |
Aerobic and anaerobic respiration
Based on the presence or absence of oxygen, respiration is of two types:
Aerobic respiration
Anaerobic respiration
Aerobic respiration
- Aerobic respiration is the release of energy from the complete oxidation of glucose in the presence of oxygen e.g., plant cells, animal cells.
- This is represented by the following overall reaction.
Anaerobic respiration
- Anaerobic respiration (anoxybiotic) is the release of energy from the incomplete breakdown of glucose in the absence of oxygen to ethanol and carbon dioxide e.g., yeast, some bacteria, muscle cells.
- The chemical reaction can be written as:
Aerobic vs anaerobic respiration in plants
The major difference between aerobic and anaerobic respiration in plants are as follows:
| Particulars | Aerobic | Anaerobic |
| Definition | Aerobic respiration uses oxygen | Anaerobic respiration is respiration without oxygen |
| Breakdown of glucose | Complete breakdown | Incomplete breakdown |
| Reactants | Glucose and oxygen | Glucose |
| Products | Carbon dioxide and water | Ethyl alcohol and carbon dioxide |
| Amount of energy released | High (38ATP) | Low (2ATP) |
| Sites of reaction | Mitochondria and cytoplasm | Cytoplasm |
Steps of gycolysis
Glycolysis is the series of ten enzyme-mediated reactions. It has two phases preparatory phase and pay off phase.
Preparatory phase or energy spending phase
Preparatory phase or energy spending phase
- It is the phase of the breakdown of glucose into the glyceraldehyde 3-phosphate.
- Phosphorylation of glucose: In this phase, glucose is phosphorylated to glucose-6-phosphate by ATP in the presence of hexokinase.
- Synthesis of fructose-6-phosphate: Glucose-6-phosphate isomerizes to fructose-6-phosphate in the phosphohexose isomerase.
- Formation of fructose 1, 6-biphosphate: Phosphorylation of fructose-6-phosphate in the presence of fructokinase.
- Splitting: Fructose1,6-bisphosphate split enzymatically into glyceraldehyde-3-phosphate and dihydroxyacetone phosphate (DHAP).
- Isomerisation of DHAP: DHAP isomerized to glyceraldehyde-3-phosphate in the presence triose phosphate isomerase enzyme.
- Oxidation and phosphorylation: In the presence of glyceraldehyde phosphate dehydrogenase, glyceraldehyde-3-phosphate is oxidized and produces NADH.
- Substrate level phosphorylation: 1,3-bisphosphoglycerate dephosphorylate in the presence of phosphoglycerate kinase and produces ATP.
- Isomerization: 3-phosphoglycerate isomerizes to 2-phosphoglycerate enzymatically.
- Dehydration: In the presence of enolase enzyme, 2-phosphoglycerate is converted into phosphoenolpyruvate. In this process, water is released.
- Formation of pyruvate: This also a substrate level phosphorylation because phosphoenol pyruvate dephosphorylates to produce pyruvate and produces ATP.
Electron transport system
Electron transport chain or system is the series of electron carriers, enzyme and cytochrome that pass electron from one to another via the redox reaction. It is the terminal oxidation.
- It consists nicotinamide adenine dinucleotide (NAD), flavin nucleotides (FAD), coenzyme Q, and cytochromes localized in F1 particles of mitochondria.
- It occurs in inner mitochondrial membrane along with cristae.
- In this process five complexes are involved namely, I- NADH-UQ reductase, II- Succinate-UQ reductase, III- -cytochrome C reductase, IV- Cytochrome C oxidase and V is connected with particles.
- In this process, NAD and FAD are reduced.
- Redox at complex I: 4 protons pumped from matrix to intermembrane space.
- Redox at complex II: Coenzyme Q picks up the electrons from complex I and II, and goes to complex III.
- Redox of complex III: 4 protons again pumped from matrix to intermembrane space and cytochrome C transports electron to the complex IV.
- Redox of complex IV: 2 protons pumped from matrix to intermembrane space and water formation occurs in the matrix.
- ATP synthase action: It pumps proton from intermembrane space to matrix and produces ATP. It is associated with oxidative phosphorylation.
Oxidative phosphorylation
Oxidative phosphorylation is the terminal oxidation of aerobic respiration. It is the process in which ATP is formed with the help of electron transferred from the electron transport chain.
particle is the site of oxidative phosphorylation. It contains ATP synthase enzyme.
When the concentration of proton is higher at than in particle, ATP synthase became active for ATP synthesis.
The energy from proton gradient is used to attach the phosphate radicle and ADP by high energy bond produce ATP.
particle is the site of oxidative phosphorylation. It contains ATP synthase enzyme.
When the concentration of proton is higher at than in particle, ATP synthase became active for ATP synthesis.
The energy from proton gradient is used to attach the phosphate radicle and ADP by high energy bond produce ATP.
NAD
NAD or nicotinamide adenine dinucleotide is coenzyme made up of two nucleotides with the phosphate group. It is found in all living beings.
- NAD carries electrons from electron donors in glycolysis, pyruvate oxidation and Kreb's cycle to electron acceptors in the electron transport chain in the mitochondrial membrane.
- In the human body, NAD is synthesized from vitamin .
- NAD delivers its electrons to a higher energy level in the chain then does FAD. As a result, NAD will provide 50% more energy than the FAD.
Krebs cycle
Krebs cycle is the series of chemical reaction to produce energy. It is used by all aerobic living organisms. It was discovered by the Hans Krebs.
- It is the process of oxydation of activated acetyl-CoA.
- It occuts in the matrix of the mitochondria.
- It is the ten stepped enzymatic pathway.
- As its first product is citric acid or citrate, it is also called as citric acid cycle.
- This pathway needs oxygen and releases lots of energy.
- In this process, two acetyl residues liberate two ATP or GTP through substrate level phosphorylation.
- It is connected with the oxydative phosphorylation.
- It produces , , , , and
Significance of Kreb's cycle and its intermediates
Kreb's cycle is the major pathway for the synthesis of coenzyme and controlled release of energy during respiration.
- It is a common pathway of oxidative breakdown of carbohydrates, fatty acids and amino acids.
- Amino acid enters the Krebs cycle directly as glutamate and aspartate after their deamination.
- It produces GTP which is important for signal transduction.
- Succinyl CoA takes part in the formation of chlorophyll.
Linked reactions
The end product of glycolysis is pyruvate that enters the mitochondria through transport protein.
- In mitochondria, pyruvic acid or pyruvate undergoes oxidative decarboxylation to produce acetyl-CoA, , .
- In this process, pyruvate combines with coenzyme A and produces acetyl-CoA.
- Acetyl-CoA is the substrate for Kreb's cycle.
Ethyl alcohol fermentation
Ethyl alcohol fermentation is the anaerobic breakdown of glucose into the alcohol.
- Pyruvic acid from glycolysis undergo decarboxylation and produces acetaldehyde.
- It occurs in the absence of oxygen.
- Acetaldehyde converts into the ethyl alcohol in the presence of alcohol dehydrogenase enzyme.
- In this process, NADH is produced.
Lactic acid fermentation
Lactic acid fermentation is the anaerobic breakdown of glucose into the lactic acid
- It occurs in lactic acid bacteria, some fungi and muscle cells.
- In this process, pyruvic acid produced in glycolysis is directly reduced by lactic acid dehydrogenase enzyme to form lactic acid.
- In this process, NADH is formed.
Respiratory quotient
Respiratory quotient is the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed in respiration over a period of time. Its value can be one, zero and more or less than one.
RQ =
Importance of RQ
RQ =
Importance of RQ
- It helps to determine respiratory substrate.
- It helps to know the type of respiration performed.
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