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Glycolysis and Krebs Cycle are two important mechanisms that are involved in the mechanism of cellular respiration. Glycolysis is a process where the two pyruvic molecules are obtained by using the partial oxidation of glucose. It is anaerobic and takes place in the cell’s cytoplasm. On the other hand, the process of the Krebs cycle is an aerobic process that produces the carbon dioxide after oxidising pyruvic acid completely which is produced during the process of glycolysis and occurs in the mitochondria of the cell.
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Key Takeaways: Glycolysis, Krebs Cycle, oxidation, ATP, respiration, mitochondria
Glycolysis
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The process of glycolysis is a first step mechanism of cellular respiration where the glucose is broken down using partial oxidation to produce two units of pyruvic acid anaerobically in the cell's cytoplasm. The acetyl CoA is condensed to produce citrate(6C) when the coenzyme is released along with the oxaloacetate(4C). For the catalysing purpose, the citrate synthase is used as an enzyme.
What is Krebs Cycle?
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The Krebs Cycle is the second process in the mechanism of cellular respiration which is responsible for degrading the pyruvic acid which is formed in the first step of glycolysis and forms the inorganic compounds like carbon dioxide and water aerobically in the cell's mitochondria. With the help of the succinate dehydrogenase enzyme, the succinate is oxidised to produce fumarate. The FAD is transformed to the FADH2 with the help of this process. The Krebs cycle is used to produce carbon dioxide using the molecules of pyruvic acid generated in the cell’s mitochondria.
Difference between Glycolysis and Krebs Cycle
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Following are the differences:
| Glycolysis | Krebs Cycle |
|---|---|
| The location where the process occurs is the cell's cytoplasm. | The location where the process occurs is the cell's mitochondria. |
| It takes place in all the living organisms | It takes place only in the aerobes |
| The carbon dioxide is not evolved during this process. | The carbon dioxide is evolved during this process. |
| It requires two ATP molecules to substance molecules for the initial phosphorylation. | It does not require any ATP. |
| It takes place in a linear sequence. | It takes place in a cyclic sequence. |
| It does not need oxygen. | It needs oxygen. |
| In this process, 4 molecules of ATP are generated by one molecule of glucose through substrate-level phosphorylation | In this process, 2 molecules of ATP and GTP are generated by two molecules of acetyl residues through substrate-level phosphorylation |
| It yields two molecules of pyruvate with the action of breaking down glucose and is the first step of respiration. | It forms water and carbon dioxide by degrading the pyruvate and is the second step of respiration. |
| For the glucose breaking down every time, it results in the formation of two molecules of NADH and ATP each. | For every molecule of acetyl-CoA being oxidised, it results in the two molecules of FADH2 and NADH. |
Points to Remember
Following are some important points:
- Through the process of respiration, any living organism intakes oxygen and releases carbon dioxide.
- Cellular respiration is the process of breaking down a cell’s macromolecules (like glucose) to generate ATP, the energy currency of the cell.
- The process of respiration has many mechanisms including the glycolysis and Krebs cycle. There are 7 mechanisms in total.
- Glycolysis is a process that is supposed to occur in the cytoplasm of a cell to produce two molecules of pyruvic acid by partial oxidation.
- The Krebs cycle differs from the glycolysis cycle in different ways such as the location of the processes.
- The Krebs cycle which takes place in the mitochondria has eight different steps.
Sample Questions
Ques: What is respiration? Name the different mechanisms required to achieve respiration. (2 Marks)
Ans: Respiration is one of the important processes required by living organisms to survive as it involves the process of intaking oxygen and releasing carbon dioxide into the atmosphere. The different mechanism in respiration includes:
- Glycolysis
- Electron Transport System
- Anaerobic Breakdown of Pyruvic Acid
- Pentose Phosphate Pathway
- Terminal Oxidation and Oxidative Phosphorylation
- Krebs Cycle
Ques: Differentiate between glycolysis and Krebs cycle in three major points. (3 Marks)
Ans: The three major points in which the glycolysis and Krebs cycle differ are:
- Definition: Glycolysis is defined as the process of yielding two molecules of pyruvate with the action of breaking down glucose. The Krebs cycle is defined as the process of forming inorganic substances like water and carbon dioxide by degrading the pyruvate.
- Location: Glycolysis occurs in the cytoplasm of the cell while the Krebs cycle takes place in the mitochondria of the cell.
- Step in the process: The glycolysis is the first step of respiration while the Krebs cycle holds second place in the respiration process.
Ques: Explain the role of pyruvate. (2 Marks)
Ans: Pyruvate is formed as an end product of the glucose metabolism and along with the ATP (adenosine triphosphate) and carbon dioxide, it gives results to acetyl-CoA and ADP(adenosine diphosphate). It is a biological substance and this of ADP and acetyl-CoA has formed at the start or the first stage of the TCA cycle. It is synthesised using pyruvic acid.
Ques: Explain glycolysis and Krebs cycle. (2 Marks)
Ques: Is the process of glycolysis a Redox and Aerobic. Explain. (2 Marks)
Ques: What is an alternative name of Glycolysis? (2 Marks)
Ans: Glycolysis can also be termed the EMP process. Gustav Embden, Otto Meyerhof, and Jakub Karol Parnas have termed the other name of the process on their respective names. The process glycolysis is used to form pyruvic acid and ATP(adenosine triphosphate) by transforming glucose in the cytoplasm.
Ques: Differentiate between glycolysis and Krebs cycle based on the ATP requirement, oxygen requirement, and the process sequence. (3 Marks)
Ans: The contrasts between the glycolysis and Krebs cycle are:
- ATP Requirement- The process of glycolysis requires two molecules of adenosine triphosphate while the Krebs cycle does not require any molecule of ATP or adenosine triphosphate.
- Oxygen Requirement- While the process of glycolysis does not need oxygen but oxygen is required for the Krebs cycle.
- Process Sequence- The glycolysis process takes place in a linear sequence while the Krebs cycle has a cyclic sequence.
Ques: Explain the steps of Krebs Cycle and Glycolysis. (6 Marks)
Ans: The process of yielding two molecules of the acetyl-CoA from every molecule of glucose is an eight-step process that produces four Co2, two ATPs, two FADH2, and six NADH. In the mitochondrial cell, the Krebs cycle consists of eight steps. The energy is released and stored in the form of ATP.
- Step1: The acetyl CoA is condensed to produce citrate(6C) when the coenzyme is released along with the oxaloacetate(4C). For the catalysing purpose, the citrate synthase is used as an enzyme.
- Step2: Citrate is converted to the isocitrate which in turn is an isomer. For the catalysing purpose, aconitase is used as an enzyme.
- Step 3: To form α-ketoglutarate, the process of dehydrogenation and decarboxylation takes place on isocitrate by releasing one molecule of carbon dioxide.
- Step 4: Succinyl CoA(4C) is formed when the oxidative decarboxylation is done of the α-ketoglutarate(5C). α-ketoglutarate dehydrogenase serves as an enzyme complex.
- Step 5: To produce GTP, this reaction is then coupled with the GDP’s substrate-level phosphate. TO yield ATP, the GTP transfers the phosphate into ADP.
- Step 6: With the help of the succinate dehydrogenase enzyme, the succinate is oxidised to produce fumarate. The FAD is transformed to the FADH2 with the help of this process.
- Step 7: Adding one molecule of H2O, the molecule of fumarate is changed into malate. The enzyme which regulates this reaction is called fumarase.
- Step 8: Oxaloacetate is formed by dehydrogenating malate that starts the new cycle by adding other molecules of acetyl CoA. NAD+ forms NADH by removing hydrogen.
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