Calvin Cycle

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Questions and Answers

What is the initial stable product of photosynthesis identified as part of the C3 pathway?

Ribulose bisphosphate (RuBP)

Phosphoglyceric acid (PGA) (correct)

Sucrose

Glucose

Which molecule acts as the primary acceptor for CO2 in the photosynthesis process?

Phosphoglyceric acid (PGA)

Ribulose bisphosphate (RuBP) (correct)

Glucose

Fructose

What process is necessary for the synthesis of ribulose bisphosphate (RuBP)?

Dark reactions

Cellular respiration

Photophosphorylation (correct)

Fermentation

Which radioactive isotope was used by Calvin to elucidate the pathway of CO2 fixation?

14C Signup and view all the answers

What was identified as the first product of the C3 pathway using radioactive carbon experiments?

Phosphoglyceric acid (PGA) Signup and view all the answers

What is required for the regeneration of ribulose 1,5-bisphosphate?

Additional ATP Signup and view all the answers

How many ATP molecules are consumed in the fixation of three CO2 molecules?

9 ATP Signup and view all the answers

What is the end product of reducing 3-phosphoglycerate in the Calvin Cycle?

Glyceraldehyde 3-phosphate (G3P) Signup and view all the answers

Which enzyme catalyzes the conversion of PGA to 1,3 BisPGA?

3-phosphoglycerate kinase (PGA kinase) Signup and view all the answers

What drives the reversal of glycolysis in the Calvin Cycle?

High concentrations of NADPH and ATP Signup and view all the answers

What products are formed alongside glyceraldehyde 3-phosphate (G3P) during the conversion of 6 PGA?

6 NADP+ and 6 ADP Signup and view all the answers

What is the net stoichiometry of CO2 assimilation in the Calvin Cycle?

3CO2 + 9 ATP + 6 NADPH Signup and view all the answers

What is the primary role of RuBP carboxylase in the Calvin Cycle?

To fix CO2 to RuBP Signup and view all the answers

What are the required inputs for the reduction stage of the Calvin Cycle?

NADPH and ATP Signup and view all the answers

What happens to PGA when CO2 is depleted?

PGA is still metabolized in light Signup and view all the answers

Which of the following is NOT a stage in the Calvin Cycle?

NADPH synthesis Signup and view all the answers

What is the end product of the reduction phase of the Calvin Cycle?

Glyceraldehyde 3-phosphate Signup and view all the answers

What is synthesized from 3 ribulose 1,5-bisphosphate and 3 CO2 during CO2 fixation?

6 x 3-phosphoglycerate Signup and view all the answers

What depletes remaining intermediates in the Calvin Cycle under light conditions?

RuBP regeneration Signup and view all the answers

Which of the following accurately describes the overall process of photophosphorylation?

It generates ATP and NADPH using light energy. Signup and view all the answers

Study Notes

The Role of Plants in Air Correction

Plants have the power to "correct" bad air by utilizing it as nourishment.
Plants absorb air spoiled by animals, improving its quality for other organisms.

Radioactive isotopes and CO2 fixation discovery

Radioactive isotopes like 11C and 14C were used to trace the pathway of carbon dioxide fixation in photosynthesis.
11C has a short half-life, while 14C is stable and ideal for long-term studies.

Elucidation of CO2 fixation pathway

The first stable product of photosynthesis is phosphoglyceric acid (PGA).
The acceptor molecule for CO2 is ribulose bisphosphate (RuBP), a 5-carbon compound.
RuBP is synthesized through a process requiring ATP and NADPH from photophosphorylation.
The pathway of carbon to sugar involves the Calvin cycle, converting CO2 into sugars like sucrose.

The Calvin Cycle: C3 photosynthesis

The Calvin cycle, also known as C3 photosynthesis, is a key pathway in plants.
It consists of three stages: CO2 fixation, reduction of 3-PGA to GAP, and regeneration of RuBP.
The first stage involves the incorporation of CO2 into RuBP, catalyzed by RuBP carboxylase.
The second stage utilizes ATP and NADPH produced during photophosphorylation to reduce 3-PGA to GAP.
The final stage regenerates RuBP, a crucial step for continuous carbon fixation.

Stoichiometry of the Calvin Cycle

Three CO2 molecules are fixed to generate one glyceraldehyde 3-phosphate (G3P), a precursor for carbohydrate synthesis.
The process consumes nine ATP molecules and six NADPH molecules.

Fate of Triose Phosphates

Triose phosphates, including GAP and DHAP, are crucial for carbohydrate biosynthesis and oxidation.
They are involved in storage, catabolism (glycolysis), and anabolism (starch and sucrose synthesis).
DHAP is translocated from the chloroplast to the cytosol in exchange for Pi, facilitating energy export.

Regulation of the Calvin Cycle

The Calvin cycle is regulated by various enzymes, including RuBP carboxylase and SBPase.
SBPase is considered the slowest step and potentially rate-limiting in the cycle.
Light activation of Calvin cycle enzymes involves thioredoxin, a small protein.
Thioredoxin reduces disulfide bonds in target enzymes, activating their function.

Key Points

RuBP carboxylase is a crucial enzyme in the Calvin cycle, responsible for attaching CO2 to RuBP.
SBPase is a key regulator of the Calvin cycle, playing a vital role in the regeneration of RuBP.
Light activation of Calvin cycle enzymes is crucial for regulating the cycle and ensuring efficient carbon fixation.
Photophosphorylation is the process by which plants use light energy to produce ATP and NADPH, essential for the Calvin cycle to function.

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Description

Explore the critical role of plants in air correction and their intricate processes in photosynthesis. This quiz covers the path of carbon dioxide fixation, the Calvin cycle, and the significance of radioactive isotopes in studying these processes. Test your understanding of how plants convert CO2 into sugars and improve air quality.