Original video: https://youtu.be/t1USGntKCfM
Delivered on: 23 OCTOBER 2023
10.1 The Calvin–Benson Cycle
A requisite for maintaining life in the biosphere is the fixation of atmospheric CO2 into organic compounds, which ultimately provide the substrates and energy needed for cellular metabolism. These endergonic (energy-requiring) transformations are driven by the energy coming from the photochemical reactions described in Chapter 9.
The predominant pathway of autotrophic CO2 fixation is termed the Calvin–Benson cycle (see WEB TOPIC 10.2), which is found in many prokaryotes and in all photosynthetic eukaryotes, from algae to angiosperms. This pathway decreases the oxidation state of carbon from the highest value, found in CO2 (+4), to levels found in sugars (e.g., +2 in keto groups [—CO—] and 0 in secondary alcohols [—CHOH—]).
In view of its notable capacity for lowering the carbon oxidation state, the Calvin–Benson cycle is also aptly named the reductive pentose phosphate cycle and the photosynthetic carbon reduction cycle. In this section we examine how CO2 is fixed via Rubisco and assimilated by the Calvin–Benson cycle using ATP and NADPH generated by the light reactions (see Figure 10.1), and how the cycle is regulated.
The Calvin–Benson cycle has three phases: carboxylation, reduction, and regeneration
In the 1950s, a series of ingenious experiments carried out by M. Calvin, A. Benson, J. A. Bassham, and their colleagues provided convincing evidence for the Calvin– Benson cycle (see WEB TOPIC 10.2). The Calvin–Benson cycle can be separated into three phases that are highly coordinated in the chloroplast.
Video Timestamps:
0:00 Introduction
10:18 Biochemical reactions in photosynthesis
12:23 Importance of Carbon Reactions
15:28 Enthalpy vs entropy
20:00 Quick recap of Light Reaction
22:09 Cyanobacterial CO2 concentrating mechanisms and Chlamydomonas cell
26:13 The Calvin-Benson cycle has three phases: carboxylation, reduction, and regeneration
35:31 The fixation of CO2 via carboxylation of ribulose 1,5-bisphosphate and the reduction of 3-phosphoglycerate yield triose phosphates
39:34 Carboxylation and oxygenation of ribulose 1,5-bisphosphate catalyzed by Rubisco.
44:33 Reduction phase of the Calvin Cycle
55:33 The regeneration of ribulose 1,5-bisphosphate ensures the continuous assimilation of CO2
Keywords: C4 photosynthesis, Calvin–Benson cycle, Crassulacean acid metabolism (CAM), Ferredoxin–thioredoxin system, Induction period, Kranz anatomy, Photorespiration, Rubisco, Starch, sucrose, C1, C2, C3, C4, CAM, Carbon Metabolism
Location:
Faculty of Agriculture, Universiti Putra Malaysia
Fakulti Pertanian, Universiti Putra Malaysia, 43000 Seri Kembangan, Selangor
XPMM+9J Seri Kembangan, Selangor
2.9845517506267742, 101.73803356324866
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