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Stroma, in botany, refers to the colorless fluid surrounding the grana within the chloroplast. [1] Within the stroma are grana (stacks of thylakoid), the sub-organelles where photosynthesis is started [2] before the chemical changes are completed in the stroma. [3] Photosynthesis occurs in two stages.
Within the envelope membranes, in the region called the stroma, there is a system of interconnecting flattened membrane compartments, called the thylakoids.The thylakoid membrane is quite similar in lipid composition to the inner envelope membrane, containing 78% galactolipids, 15.5% phospholipids and 6.5% sulfolipids in spinach chloroplasts. [3]
The cytochrome b 6 f complex is a dimer, with each monomer composed of eight subunits. [3] These consist of four large subunits: a 32 kDa cytochrome f with a c-type cytochrome, a 25 kDa cytochrome b 6 with a low- and high-potential heme group, a 19 kDa Rieske iron-sulfur protein containing a [2Fe-2S] cluster, and a 17 kDa subunit IV; along with four small subunits (3-4 kDa): PetG, PetL, PetM ...
[6] [2] Furthermore, in the absence of light (and thus photosynthesis), chlororespiration plays an integral role in enabling metabolic pathways to compensate for chemical energy synthesis. [2] This is achieved through the oxidation of stromal compounds, which increases the PQ pool and allows for the chlororespiratory ETC to take place. [2] [6]
In cyclic photophosphorylation, cytochrome b 6 f uses electrons and energy from PSI to create more ATP and to stop the production of NADPH. Cyclic phosphorylation is important to create ATP and maintain NADPH in the right proportion for the light-independent reactions. The net-reaction of all light-dependent reactions in oxygenic photosynthesis ...
In general outline, photosynthesis is the opposite of cellular respiration: while photosynthesis is a process of reduction of carbon dioxide to carbohydrates, cellular respiration is the oxidation of carbohydrates or other nutrients to carbon dioxide. Nutrients used in cellular respiration include carbohydrates, amino acids and fatty acids.
The thylakoid membranes of higher plants are composed primarily of phospholipids [5] and galactolipids that are asymmetrically arranged along and across the membranes. [6] Thylakoid membranes are richer in galactolipids rather than phospholipids; also they predominantly consist of hexagonal phase II forming monogalacotosyl diglyceride lipid.
Rates of leaf photosynthesis were shown to increase by 30–50% in C3 plants, and 10–25% in C4 under doubled CO 2 levels. [40] The existence of a feedback mechanism results a phenotypic plasticity in response to [CO 2 ] atm that may have been an adaptive trait in the evolution of plant respiration and function.