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Essay Unit 10 - Biological Molecules and Metabolic Pathways C
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UNIT 10Biological Molecules and Metabolic Pathways
Assignment C
C1 Pathways in photosynthesis
Plants and other organisms use photosynthesis to transform light energy into
chemical energy that is then used for cellular respiration.
Photosynthesis occurs in two stages: The light-dependent and light-independent
stages
The light-dependent process that occurs in the thylakoids. Thylakoids are elongated
sacs within chloroplasts that are surrounded by pigmented membranes where light
reactions occur. This is where photophosphorylation occurs. Photophosphorylation is
another name for the light-dependent step.
Photophosphorylation stages: (coenzymes during this stage are NADPH and ATP)
This is non-cyclic photophosphorylation:
(1)
In the thylakoid lumen, light energy is used to break down water (photolysis) to
create hydrogen ions, electrons, and oxygen.
A proton gradient is produced due to the photolysis of water resulting in a high
concentration of hydrogen ions in the thylakoid lumen.
Within the membrane, electrons move through an electron transport chain of
proteins.
When hydrogen ions in the stroma and electrons from the electron transport chain
join with the carrier molecule NADP, reduced NADPH is formed.
Photophosphorylation, which uses the proton gradient between the thylakoid lumen
and stroma to activate the enzyme ATP synthase, produces ATP.
Photophosphorylation converts light energy into chemical energy in the shape of
ATP.
, UNIT 10
Biological Molecules and Metabolic Pathways
The Calvin cycle, also known as the light independent period.
The Calvin cycle is a process that plants and algae use to convert carbon dioxide from
the air into sugar, which autotrophs require to develop. The Calvin cycle is essential
to all living things on Earth. The Calvin cycle provides energy and sustenance to
plants.
Carbon fixation: The Calvin cycle starts when a CO2 molecule is attached to ribulose
bisphosphate, a five-carbon sugar. (RuBP). Ribulose bisphosphate carboxylase is the
enzyme that catalyses this activity. (Or rubisco). Unsurprisingly, rubisco is the most
common protein on the planet. This reaction produces a highly unstable 6 carbon
intermediate, which quickly splits into two 3 carbon sugars. (3-phosphoglycerate,
also called 3-PGA). Each molecule of CO2 produces two molecules of 3-PGA. The
quantity of carbon atoms does not change.
Reduction: An ATP phosphate group is integrated into each 3-PGA molecule,
resulting in 1,3-biphosphoglycerate. Following this, phosphate is eliminated and 1,3-
biphosphoglycerate is reduced, yielding glyceraldehyde-3-phosphate. (G3P). NADPH
provides the electron pair needed for this reduction. When ATP is converted to ADP
and NADPH is converted to NADP+, energy is supplied for this process. Both of these
compounds are then recycled through light-dependent reactions. Step 3 involves the
regeneration of RuBP. This is accomplished through a complicated series of reactions
that transforms 5 G3P (5x 3 carbons) molecules into 3 RuBP molecules. (3x 5
carbons). This mechanism requires at least three molecules of ATP.
Role of RuBP: RuBP, or ribulose bisphosphate, is a 5-carbon compound that
participates in the Calvin cycle, which is one of photosynthesis's light-independent
processes. Atmospheric carbon dioxide is combined with RuBP via an enzyme called
RuBisCO to produce a 6-carbon molecule.
RuBisCo is the enzyme responsible for the fixation of carbon derived from
atmospheric CO2 as part of the Calvin-Benson cycle, which results in the creation of
glucose, which is required for development in most photosynthetic organisms.
Glucose synthesis:
Three carbon units, TP (triphosphate), are converted to glucose.
One carbon molecule is acquired from top for each cycle turn.
One molecule of glucose requires six Calvin cycle steps. Glucose is 6 carbons (C6).
Rubisco leads to the production of glucose.
[2], [3], [4]
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