Name: photorespiration, c4, and cam pathways
Uploaded: 2023-04-30T09:16:56.000Z
Duration: 1 min 46 s
Channel: JoVE

K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Biology

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From Molecules to Organisms- Structures and Processes

LS.Bio.3.2

The Calvin Benson Cycle

The Calvin-Benson cycle is the second phase of photosynthesis, where plants use ATP and NADPH&#8212;the end products of the light reactions&#8212;to form sugar.
This series of reactions is subdivided into three stages.
During the carbon fixation stage, ribulose-1,5-bisphosphate carboxylase/oxygenase or RuBisCo catalyzes the addition of CO2 to a five-carbon sugar, ribulose 1,5-bisphosphate or RuBP, therefore fixing inorganic CO2 into an organic molecule.&#160;
&#160;This reaction generates an unstable six-carbon intermediate, which is further cleaved into two small three-carbon molecules called 3-phosphoglycerate or 3-PGA.&#160;
In the reduction stage, 3-phosphoglycerate kinase adds a phosphate to the carboxyl group of 3-PGA, yielding 1,3-bisphosphoglycerate.
Then, glyceraldehyde 3-phosphate dehydrogenase transfers electrons from NADPH to 1,3-bisphosphoglycerate, producing two molecules of glyceraldehyde-3-phosphate or G3P.
One G3P leaves the Calvin-Benson cycle to form essential plant metabolites, and the other undergoes a complex set of reactions along with ATP to regenerate RuBP.&#160;
Overall, it takes 6 CO2 molecules in the fixation stage, 12 ATP and 12 NADPH in the reduction stage, and 6 ATP in the regeneration stage to produce one six-carbon sugar.

the calvin benson cycle

Ribulose 1,5- bisphosphate carboxylase/oxygenase (RuBisCo) is a critical enzyme that catalyzes carbon dioxide assimilation during photosynthesis. However, it is an inefficient enzyme, having an extremely slow catalytic rate. A typical enzyme can process about a thousand molecules per second; however, RuBisCo fixes only around three-carbon dioxides per second. Photosynthetic cells compensate for this slow rate by synthesizing very high amounts of RuBisCo, making it the most abundant single enzyme on Earth.
In addition, RuBisCo has a poor substrate specificity due to which oxygen can easily attach to the carbon dioxide binding site of the enzyme. As a result, an abnormal molecule is produced along with the release of CO2. This process is called photorespiration or, more accurately- oxidative photosynthetic carbon cycle.
Every photosynthetic organism experiences a basal level of photorespiration; however, under high intracellular oxygen levels, photorespiration exceeds photosynthesis. Most tropical plants have developed a mechanism to circumvent the wasteful photorespiration through a special process that increases the intracellular CO2 levels. In such plants, the Calvin cycle&#39;s usual carbon fixation step is preceded by several steps that temporarily fix CO2 by forming four-carbon intermediates such as oxaloacetate and malate. The plants that rely on this process are called C4 plants, and the assimilation process is termed the C4 pathway.
Another variation of CO2 fixation is observed in succulent plants that grow in hot and arid environments. In these plants, stomata remain closed during the daytime to prevent loss of water from the plants. Because closure of stomata also prevents gas molecules from entering the leaf, CO2 is absorbed during night-time when cool and moist air enables opening of stomata. CO2 trapped overnight in the form of malate is released during the daytime by the NADP-linked malic enzymes. Because this method of CO2 assimilation was first discovered in the plants of the Crassulaceae family, it is called crassulacean acid metabolism, or CAM pathway.

Ribulose 1,5- bisphosphate carboxylase/oxygenase (RuBisCo) is a critical enzyme that catalyzes carbon dioxide assimilation during photosynthesis. However, ...

Education

JoVE Core

Cell Biology

Unit 1

Chloroplasts and Photosynthesis

KEY TERMS AND CONCEPTS

photorespiration, c4, and cam pathways

Photorespiration and the C4 and CAM pathways change how plants handle carbon dioxide during photosynthesis. These processes matter because RuBisCo, the enzyme that starts carbon dioxide fixation, works very slowly. A typical enzyme can process about a thousand molecules per second, but RuBisCo fixes only around three carbon dioxides per second. To make up for this slow rate, photosynthetic cells produce very large amounts of RuBisCo. That is why it is the most abundant single enzyme on Earth.

RuBisCo also has poor substrate specificity. This means oxygen can attach to the same site where carbon dioxide should bind. When that happens, an abnormal molecule is formed and CO2 is released. This wasteful process is called photorespiration, or more accurately, the oxidative photosynthetic carbon cycle. Every photosynthetic organism has a basal level of photorespiration, but it can become greater than photosynthesis when oxygen levels inside the cell are high.

Most tropical plants reduce photorespiration with the C4 pathway. In these plants, the normal carbon fixation step of the Calvin cycle is preceded by several steps that first trap CO2 in four-carbon intermediates such as oxaloacetate and malate. This raises the CO2 level inside the cell before the Calvin cycle begins. The plants that use this strategy are called C4 plants.

Succulent plants in hot, dry environments use another strategy called crassulacean acid metabolism, or the CAM pathway. Their stomata stay closed during the day to limit water loss. Because closed stomata also block gas entry, these plants take in CO2 at night when the air is cooler and more moist. The CO2 is stored overnight as malate and then released during the day by NADP-linked malic enzymes.

Photorespiration, C4, and CAM Pathways

what is photosynthesis?

Photosynthesis Powers the Food Chain

Photosynthesis powers the food chain by turning sunlight into usable chemical energy. It is the only biological process that can capture energy from sunlight and convert it into chemical energy that organisms use to support metabolism. Photosynthesis also provides the oxygen needed by many living things. Organisms are often grouped by how they get food. Autotrophs are organisms that make their own food. Plants, algae, and cyanobacteria are autotrophs, and because they use light to make...

the anatomy of chloroplasts

How Chloroplasts Power Photosynthesis

Chloroplasts are the organelles that power photosynthesis in green algae and plants. They are found in green stems and unripe fruit as well as in leaves. Inside chloroplasts, the two stages of photosynthesis work together to turn sunlight, carbon dioxide, and water into chemical energy. The light-dependent reactions capture sunlight and release oxygen. They also make ATP and NADPH, which are energy-rich molecules. The light-independent reactions then use ATP and NADPH to capture CO2 and build...

Photorespiration and the C4 and CAM pathways change how plants handle carbon dioxide during photosynthesis. These processes matter because RuBisCo, the enzyme that starts carbon dioxide fixation, works very slowly. A typical enzyme can process about a thousand molecules per second, but RuBisCo fixes only around three carbon dioxides per second. To make up for this slow rate, photosynthetic cells produce very large amounts of RuBisCo. That is why it is the most abundant single enzyme on Earth. <br...

the photochemical reaction center

Light-Harvesting Antennas in Reaction Centers

Light-harvesting antennas and reaction centers work together in photosynthesis. A reaction center is a pigment-protein complex that starts the conversion of light energy into chemical energy. The term photochemical reaction center is more precise because these complexes carry out the first light-driven chemical step. Robert Emerson and William Arnold gave the first experimental evidence for these centers. They showed that nearly 2,500 chlorophyll molecules were involved in the release of just...

the antenna complex

Light-Harvesting in Photosynthesis

Light-harvesting in photosynthesis depends on the antenna complex, also called the light-harvesting complex (LHC). Plants and other photosynthetic organisms use this system to collect direct sunlight with pigments in both the reaction center and the antenna complex. The reaction center is the main site of photochemical reactions. Under average light conditions, the reaction center pigments absorb light more slowly than the electron transport chain can use it. The reaction center alone cannot...

photosystems

Photosystems in Light Reactions

Photosystems are pigment-rich protein complexes that help drive the light reactions of photosynthesis in plants, algae, and cyanobacteria. They are embedded in the thylakoid membrane inside the chloroplast. Their job is to capture light energy and pass it along for chemical use. Each photosystem contains many pigment molecules, including chlorophylls and carotenoids. These pigments are arranged in two parts: the antenna complex and the reaction center. The antenna complex absorbs photons and...

the z-scheme of electron transport in photosynthesis

the-z-scheme-of-electron-transport-in-photosynthesis

How Electron Flow Powers the Z-Scheme

The Z-scheme explains how electrons move through the light reactions of photosynthesis. In this process, light energy drives electrons from water to NADP+, and oxygen is released when water splits. Because water is hard to oxidize, the reaction needs a strong oxidizing agent. That role is filled by oxidized P680, also called P680+. It is the first product of the light reactions and is known as the most powerful oxidizing agent in biology. After it gains an electron from water-splitting, P680+...

key terms and concepts

Learn how photorespiration affects photosynthesis and how C4 and CAM plants reduce it by trapping carbon dioxide in different ways.

Photorespiration, C4, and CAM Pathways | JoVE K12

cell biology

JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

Pennsylvania State Academic Standards

Life Science

matter-and-energy-in-organisms-and-ecosystems

Matter and Energy in Organisms and Ecosystems

3.1.9-12.E

3.1.9-12.J

3.1.9-12.K

Louisiana Student Standards for Science

High School

Life Sciences

From Molecules To Organisms: Structures And Processes

HS-LS1-5

ecosystems-interactions-energy-and-dynamics

Ecosystems: Interactions, Energy And Dynamics

HS-LS2-1

Environmental Science

HS-LS2-4

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Ohio’s Learning Standards and Model Curriculum

Cells

Cellular processes

Tennessee Academic Standards

From Molecules to Organisms: Structures and Processes

BIO1.LS1.8

Virginia  Standards of Learning

HIgh School

BIO.2

BIO.2.e

Minnesota Academic Standards in Science

3.1.1 9L.3.1.1.2

3.2.1 9L.3.2.1.3

new-jersey-student-learning-standards-for-science

New Jersey Student Learning Standards for Science

Arizona Science Standards

HS.L2

HS.L2U1.21

HS+B.L2

HS+B.L2U1.8

Alabama Course of Study Science

9-12.B.1.5.b

Florida Department of Education

SC.912.L.18

SC.912.L.18.7

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

B-LS1-5

Georgia Standards of Excellence

Botany

SBO1.

Photosynthesis

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Photorespiration, C4, and CAM Pathways

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