Difference Between Grana and Stroma | Definition, Structure, Function
Deep inside the chloroplasts of plant cells we find granum, or the stacks tunnels in the lower part of thylakoid stacks called stromal thylakoids. A granum is a stack of thylakoids in the chloroplast. The stroma is the gel-like material that surrounds the grana inside the chloroplast. Small-angle neutron scattering peak arising from stroma lamellae is identified. 1) between units in the grana stack (i.e. the height of a granum thylakoid plus the height of the . Thylakoid membranes were freshly isolated either from market spinach .. 6b shows the difference in repeat distance between the original dark .
Whereas some stroma thylakoids form solid, sheet-like bridges between adjacent grana, others exhibit a branching geometry with small, more tubular sheet domains also connecting adjacent, parallel stroma thylakoids.
We postulate that the tremendous variability in size of the junctional slits may reflect a novel, active role of junctional slits in the regulation of photosynthetic function. In particular, by controlling the size of junctional slits, plants could regulate the flow of ions and membrane molecules between grana and stroma thylakoid membrane domains. The term thylakoid is the name coined by Menke to describe the internal photosynthetic membranes of chloroplasts.
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Most of our knowledge of the three-dimensional 3D architecture of higher-plant thylakoids is based on the analysis of electron micrographs of thin-sectioned in situ and isolated chloroplasts Staehelin, The first electron micrographs of thin-sectioned chloroplasts in which the internal thylakoid membranes were clearly resolved indicated that they were organized in the form of flat sheets and membrane stacks Hodge et al.
Menke subsequently postulated that higher-plant chloroplasts contained many individual, sac-like thylakoids of two types, small thylakoids that gave rise to the grana stacks, and large thylakoids now called stroma thylakoids that interconnected the grana stacks.
- Difference Between Grana and Stroma
Heslop-Harrison and Wehrmeyerto our knowledge, were the first to show that the stroma thylakoids were arranged in a spiral-like configuration around grana stacks, and that at each grana-stroma membrane intersection the two membranes were fused together. Their models set the stage for the classic studies of Paolillo and coworkers Paolillo et al. Although these freeze-fracture and scanning electron microscopy studies provided interesting new perspectives on the 3D architecture of grana and stroma thylakoids, they did not yield any new insights necessitating major revisions to the Paolillo model.Photosynthesis and the Teeny Tiny Pigment Pancakes
An alternative model known as the forked or folded membrane model originated from an attempt to illustrate in a simple diagram how PSI and PSII are segregated into stroma and grana membrane domains Andersson and Anderson, ; Anderson and Andersson, More recently, a computerized version of this model was developed Arvidsson and Sundby, to explain the rapid, cation-induced changes in chlorophyll-a fluorescence Briantais,which have been postulated to reflect changes in membrane architecture related to unstacking and restacking of the thlakoid membranes.
Due to the approximately fold-higher z axis resolution of electron tomography 6—8 nm compared to serial thin-section electron microscopy — nm; McIntosh et al. A single chloroplast may contain 10 to grana. Grana are connected with each other by stromal thylakoids. Therefore, all grana in a particular chloroplast may act as a single functional unit.
Stromal thylakoids are also called intergranal thylakoids or lamellae.
Both thylakoid and stromal thylakoid contain photosynthetic pigments on their surfaces. On that account, the light reaction of photosynthesis occurs on the surface of grana. A granum is shown in figure 1. Granum Thylakoid is a round pillow-shaped stack inside the chloroplast. The space between thylakoid membrane is called thylakoid lumen.
What is the relationship between the granum and the stroma? | Yahoo Answers
Chlorophyll and other photosynthetic pigments are held by membrane proteins on the surface of the thylakoid. They are organized into photosystem 1 and 2 on the thylakoid membrane. Plastoquinone shuttles electrons from photosystem II to the cytochrome b6f complex, whereas plastocyanin carries electrons from the cytochrome b6f complex to photosystem I.
Together, these proteins make use of light energy to drive electron transport chains that generate a chemiosmotic potential across the thylakoid membrane and NADPHa product of the terminal redox reaction. Photosystem These photosystems are light-driven redox centers, each consisting of an antenna complex that uses chlorophylls and accessory photosynthetic pigments such as carotenoids and phycobiliproteins to harvest light at a variety of wavelengths.
Each antenna complex has between and pigment molecules and the energy they absorb is shuttled by resonance energy transfer to a specialized chlorophyll a at the reaction center of each photosystem.
When either of the two chlorophyll a molecules at the reaction center absorbs energy, an electron is excited and transferred to an electron-acceptor molecule. The P is short for pigment and the number is the specific absorption peak in nanometers for the chlorophyll molecules in each reaction center. Cytochrome b6f complex[ edit ] Main article: Cytochrome b6f complex The cytochrome b6f complex is part of the thylakoid electron transport chain and couples electron transfer to the pumping of protons into the thylakoid lumen.
Energetically, it is situated between the two photosystems and transfers electrons from photosystem II-plastoquinone to plastocyanin-photosystem I. It is integrated into the thylakoid membrane with the CF1-part sticking into stroma. Thus, ATP synthesis occurs on the stromal side of the thylakoids where the ATP is needed for the light-independent reactions of photosynthesis.
Lumen proteins[ edit ] The electron transport protein plastocyanin is present in the lumen and shuttles electrons from the cytochrome b6f protein complex to photosystem I. While plastoquinones are lipid-soluble and therefore move within the thylakoid membrane, plastocyanin moves through the thylakoid lumen. The lumen of the thylakoids is also the site of water oxidation by the oxygen evolving complex associated with the lumenal side of photosystem II. Lumenal proteins can be predicted computationally based on their targeting signals.
However, during the course of plastid evolution from their cyanobacterial endosymbiotic ancestors, extensive gene transfer from the chloroplast genome to the cell nucleus took place.
This results in the four major thylakoid protein complexes being encoded in part by the chloroplast genome and in part by the nuclear genome. Plants have developed several mechanisms to co-regulate the expression of the different subunits encoded in the two different organelles to assure the proper stoichiometry and assembly of these protein complexes.
What is the relationship between the granum and the stroma?
For example, transcription of nuclear genes encoding parts of the photosynthetic apparatus is regulated by light. Biogenesis, stability and turnover of thylakoid protein complexes are regulated by phosphorylation via redox-sensitive kinases in the thylakoid membranes. The redox state of the electron carrier plastoquinone in the thylakoid membrane directly affects the transcription of chloroplast genes encoding proteins of the reaction centers of the photosystems, thus counteracting imbalances in the electron transfer chain.
Most thylakoid proteins encoded by a plant's nuclear genome need two targeting signals for proper localization: