Calvin cycle

A thorough presentation on Calvin Cycle

1. SARDAR PATEL MAHAVIDYALAYA CHANDRAPUR DEPARTMENT OF MICROBIOLOGY (Session 2020-2021) A SEMINAR ON CALVIN CYCLE PRESENTED BY DEEPAK CHAWHAN (M.Sc. I Yr. Semester I)

2. Energy can neither be created nor destroyed ;  Energy can  only be transferred or changed from one form to another....

3. 3 Photosynthesis: An Overview The net overall equation for photosynthesis is: Photosynthesis occurs in 2 “ stages ” : The Light Reactions (or Light-Dependent Reactions) The Calvin Cycle (or Calvin-Benson Cycle or Dark Reactions or Light-Independent Reactions) 6 CO 2 + 6 H 2 O C 6 H 12 O 6 + 6 O 2 light Is photosynthesis an ENDERGONIC or EXERGONIC reaction?

4. 4 To follow the energy in photosynthesis, light light ATP NADPH Light Reactions thylakoids Calvin Cycle stroma Organic compounds (carbs) Photosynthesis: An Overview

5. 5 The Calvin Cycle Sir Melvin Calvin “Matter  can change form through physical and chemical changes, but through any of these changes,  matter is  conserved.”

6. 6 Phase 2: The Calvin Cycle Within the Calvin Cycle, chemical energy (from the light reactions i.e. ATP/NADPH) and CO 2 (from the atmosphere ) are used to produce organic compounds (like glucose ). The Calvin Cycle occurs in the stroma of chloroplasts. The Calvin Cycle occurs in the 3 steps: Carbon Fixation, Reduction, and Regeneration of RUBP.

7. 7 Phase 2: The Calvin Cycle Step 1 - Carbon Fixation. This is the process of assimilating carbon from a non-organic compound (i.e. CO 2 ) and incorporating it into an organic compound (i.e. carbohydrates). CARBON FIXATION

8. 8 Phase 2: The Calvin Cycle Step 1: Carbon Fixation Consider only 1 stroma 1 molecules of CO 2 (from the atmosphere) are joined to 1 molecules of RuBP (a 5-carbon sugar) by Rubisco (an enzyme also known as RuBP carboxylase ) Simulataneously Consider other 5 stroma 5 molecules of CO 2 (from the atmosphere) are joined to other 5 molecules of RuBP (a 5-carbon sugar) by Rubisco (an enzyme also known as RuBP carboxylase ) C C C C C C C C C C C C C C C C C C 6 carbon dioxide molecules 6 RuBP molecules Rubisco Point to Note: -One Cycle binds One Co2 with One RUBP within one Stroma C C C C C C C C C C C C C C C C C C

9. 9 Phase 2: The Calvin Cycle Step 2: Reduction Each of the 6-carbon molecules within stroma are very unstable which gets split in half, forming Two 3-carbon molecules (i.e. a Total Six 6- Carbon molecules produces Twelve 3- Carbon molecules). These molecules are then reduced by gaining electrons from NADPH. ATP is required for this molecular rearranging C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C NADPH NADP + ATP ADP P Where did the NADPH and ATP come from to do this? C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C

10. 10 Phase 2: The Calvin Cycle There are now twelve 3-carbon molecules, which are known as G3P or PGAL ( Glyceraldehyde 3 Phosphate). Since the Calvin Cycle started with 30 carbons {(i.e. 6 x 5-carbon molecules (RUBP) = 30 Carbons} and there are now 36 carbons {(i.e. 12 x 3-carbon molecules (G3PL) = 36 Carbons}, we have a net gain of 6 carbons. C C C C C C C C C C C C C C C C C C Where did these 6 extra carbons come from? Two of these “ extra ” 3-carbon G3P/PGAL molecules will exit the cycle . C C C C C C C C C C C C C C C C C C

11. 11 Phase 2: The Calvin Cycle The Calvin Cycle “ turns ” 6 times, those 2 molecules of G3P (a 3-carbon carbohydrate) will combine to form 1 molecule of glucose (a 6-carbon carbohydrate molecule) OR another organic compound. C C C G3P (from 6 turns of the Calvin Cycle) C C C G3P (from 6 turns of the Calvin Cycle) C C C C C C glucose

12. 12 Phase 2: The Calvin Cycle Step 3: Regeneration of RuBP Since this is the Calvin Cycle , we must end up back at the beginning. The remaining 10 G3P molecules (3-carbons each) get rearranged (using ATP ) to form 6 RuBP molecules (5-carbons each). 10 G3P molecules Total: 30 carbons 6 RuBP molecules Total: 30 carbons Where does the ATP come from to do this? ATP ADP P C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C

13. Phase 2: The Calvin Cycle Rubisco ORGANIC COMPOUND NADPH NADP + ATP ADP P RuBP CO 2

14. 14 Phase 2: The Calvin Cycle

15. 15 Phase 2: The Calvin Cycle Summary: In the Calvin Cycle, energy and electrons from the Light Reactions (in the form of ATP and NADPH ) and carbon dioxide from the atmosphere are used to produce organic compounds. The Calvin Cycle occurs in the stroma inside the chloroplasts (inside the cells…). Carbon dioxide, ATP, and NADPH are required (reactants). Organic compounds (G3P) are produced (products).

16. 16 Photosynthesis: A Recap So, as a broad overview of photosynthesis, The Light Reactions (Phase 1) capture the energy in sunlight and convert it to chemical energy in the form of ATP and NADPH through the use of photosystems , electron transport chains, and chemiosmosis . The Calvin Cycle (Phase 2) uses the energy transformed by the light reactions along with carbon dioxide to produce organic compounds.

17. 17 Photosynthesis: A Recap Based on this equation, how could the rate of photosynthesis be measured? The photosynthetic equation: light Excites electrons during the light reactions 6 H 2 O Split during the light reactions to replace electrons lost from Photosystem II 6 CO 2 Provides the carbon to produce organic compounds during the Calvin Cycle Produced as a byproduct of the splitting of water during the light reactions 6 O 2 C 6 H 12 O 6 The organic compound ultimately produced during the Calvin Cycle

18. References: - Principles of Biochemistry (6 th Edition), by Leninger ; Page No. 810-812. Biology of Microorganisms (14 th Edition), by Brock; Page No. 390-392. Plant Physiology (3 rd Edition ) , by Taiz & Zeiger ; Page No. 146-150.