The key difference between Krebs and Calvin cycle is that Krebs cycle is a part of aerobic respiration process which produces ATP while Calvin cycle is a part of photosynthesis which produces foods by consuming ATP.
Biochemical pathways are extremely important processes to maintain the life on Earth. Krebs and Calvin cycles are two very important biochemical pathways occurring inside the organelles of cells. Both these processes are cyclic, but there are many differences between them. The places that these processes take place and the consumption or production of energy are different from each other.
CONTENT
1. Overview and Key Difference
2. What is Krebs Cycle
3. What is Calvin Cycle
4. Similarities Between Krebs and Calvin Cycle
5. Side by Side Comparison – Krebs vs Calvin Cycle in Tabular Form
6. Summary
What is Krebs Cycle?
Krebs cycle is simply a part of the aerobic respiration process that takes place in cells. Production of carbon dioxide and ATP (adenosine triphosphate) with some other by-products occurs during the whole process of cellular respiration and Krebs cycle is an important part of that. Organisms store energy in the form of ATP. The process is known by many different names such as Citric acid cycle, Tricarboxylic acid cycle, or Krebs cycle. But all these names refer to one process. Since most types of organisms are aerobic (plants, animals, microorganisms), the Krebs cycle takes place in all these aerobic organisms.
Figure 01: Krebs cycle
Krebs cycle is a vital step in the respiratory pathway where Acetyl coenzyme A is broken down with oxygen that leads to release energy to produce ATP molecules. However, Acetyl coenzyme A is produced from the respiratory substrates such as glucose, amino acid, or fats. This process does not operate in the absence of oxygen and the respiratory substrates are broken down in the Krebs cycle. Since this cycle involves both breakdown (catabolic) and synthesis (anabolic) steps, it is known as an amphibolic pathway. The whole process has been named after Hans Krebs, who won the Nobel Prize in 1953 for the discovery of it.
What is Calvin Cycle?
Calvin cycle is a vital step in the dark reaction of photosynthesis that occurs in the stroma of the chloroplast of green plants. It is a cyclic biochemical pathway which proceeds with the use of carbon dioxide and the production of oxygen. As per the definition, Calvin cycle is a set of reactions taking place in the dark reaction of the photosynthesis, which means that it does not require sunlight. The activation of electrons does not take place in the Calvin cycle. But the necessary energy requirements for the processes are fulfilled by the consumption of ATP.
Figure 02: Calvin cycle
Overall, this cycle is an anabolic pathway, which forms glucose from carbon dioxide and water. However, the produced carbohydrates in the Calvin cycle are not hexose sugars (glucose with six carbons) according to the latest discoveries; they are triose (three-carbon) sugar phosphates, aka triose phosphates. Later, it leads to produce hexose sugars in the mitochondria.
What are the Similarities Between Krebs and Calvin Cycle?
- Krebs cycle and Calvin cycle are two important biochemical pathways.
- CO2 and ATP are involved in both processes.
- Both occur in plants.
- Both are cyclic processes that occur inside the cells.
What is the Difference Between Krebs and Calvin Cycle?
Krebs cycle is a part of aerobic respiration process while Calvin cycle is a part of photosynthesis. Former is a catabolic process while the latter is an anabolic process. Moreover, Krebs cycle occurs in the matrix of mitochondria while Calvin cycle occurs in the stroma of chloroplasts. Krebs cycle occurs in aerobic organisms. It produces ATP and CO2. Most importantly, it occurs in the presence of oxygen. However, Calvin cycle takes place only in plants. It uses ATP and CO2 and produces glucose. Furthermore, this process does not require oxygen.
Summary
Krebs cycle and Calvin cycle are two important biochemical pathways. Krebs cycle produces energy in the form of ATP. It breaks down glucose in the presence of oxygen. This process happens in all aerobic organisms including plants. Calvin cycle is a part of photosynthesis. It is known as dark reaction as well since it is independent of the sunlight, unlike light reaction. It produces glucose utilizing CO2 and ATP. This is the difference between Krebs cycle and Calvin cycle.
Reference:
1.“Boundless Microbiology.” Lumen, Open SUNY Textbooks, Available here.
2.“Photosynthesis: Calvin Cycle.” Khan Academy, Khan Academy, Available here.
Image Courtesy:
1. “Citric acid cycle noi” By Narayanese (talk) – Modified version of Image:Citricacidcycle_ball2.png (CC BY-SA 3.0) via Commons Wikimedia
2. “Calvin-cycle4” By Mike Jones – Eget arbejde (CC BY-SA 3.0) via Commons Wikimedia