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What Is The Calvin Cycle?
What is it?
Photosynthesis is the process by which plants and other autotrophs make their own "food". The calvin cycle is 1 of the 2 main parts of this process. It is also known as "the dark reactions" because it does not need light to occur.
The Calvin (or Calvin-Benson) cycle is the cyclic pathway of metabolic reactions that occur as part of photosynthesis to create glucose and other sugars using products from the light energy (most commonly sunlight) dependent part of it. It is named after the scientist(s) who first worked it out.
The Calvin cycle is the light independent reaction of photosynthesis. This is an important detail to note because it does not compile photosynthesis. There is also a light dependent stage that requires light energy.
Steps of the Calvin Cycle
- 3 Carbon Dioxide (one carbon) molecules combine with 3 ribulose biphosphate (RuBp) (5 carbon) molecules.
- This forms into 3 (6 carbon) molecules which is unstable and quickly breaks down into 6 (3 carbon) molecules: glycerate 3-phosphate (GP)
- This 3 carbon compound is reduced (given electrons) to form 6 (3-carbon) sugar phosphates named glyceraldehyde 3-phosphate (GALP).
The hydrogen (which gives the electrons for reduction) is taken from reduced NADP which was obtained during the light dependent stage of photosynthesis. Also taken from the light dependent reactions is the ATP used to provide energy for this reaction.
- one out of every 6 GALPS made are used to create a 6-carbon sugar (hexose) which may be converted into other necessary organic compounds such as amino acids or lipids.
- The remaining 5 GALP (3 carbon molecules) uses energy formed by hydrating ATP into ADP in order to rearrange themselves into 3 RuBp molecules again.
- The process repeats.
How ATP produces energy
ATP - Adenosine Triphosphate is compiled of one molecule of adenine (an organic base), one ribose (a pentose sugar) and three phosphate groups.
The third phosphate group on ATP is only loosely bonded to the second phosphate and is relatively easy to remove. When this phosphate is removed from ATP, then ADP (adenosine diphosphate) is made. The now open second phosphate group will bond easily with water molecules and become hydrated.
When bonds form, energy is released and so the formation of the bonds between the second phosphate of ADP and water molecules releases a lot of energy.
The enzyme ATPase catalyses the reaction of ATP breaking down into ADP.
Hope this hub helped some of you confused students out there!