Difference Between Grana and Thylakoid | Definition, Function, Relationship
ions and membrane molecules between grana and stroma thylakoid membrane domains. The term thylakoid is the .. connection is seen as the slice level progresses to slice. 20 (Fig. 4C) and .. (Whole Food Market) and used the same day. In terms of membrane protein content, the stacked grana thylakoids consist .. in wild-type market spinach, both in whole, cryo-sectioned chloroplasts and . An explanation for the relationship between salt-induced thylakoid. Components of a typical chloroplast. 1 Granum 2 Chloroplast envelope. Outer membrane .. "Vipp1 deletion mutant of Synechocystis: A connection between bacterial phage shock and thylakoid biogenesis?". Proc Natl Acad Sci USA. 98 (7 ).
While this model has been widely accepted, it has also been criticized for not allowing the extensive reorganization of thylakoid membranes that is known to happen under changing light conditions Arvidsson and Sundby, Instead, a less complex alternative model based on EM of plastic-embedded sections was proposed Fig.
In this simpler model, a granum is composed of piles of repetitive units, each containing three grana discs, which are formed by symmetrical invaginations of a thylakoid pair. View large Download slide Models of thylakoid organization.
C In the model of Shimoni et al. A pair of disks is formed by a bifurcation of a lamellar stroma thylakoid in the cylinder of stacked grana membranes. In each pair, the upper disk bends upwards to fuse with next pair in the stack, and the lower disk bends down on the opposite side to fuse with the disk below. Another model of thylakoid organization in chloroplasts was based on electron tomography of thin plastic sections of freeze-substituted material Shimoni et al.
In this model, the grana disks were presented as paired units formed by bifurcation of stroma thylakoids. In each pair, the upper disk bends upwards to fuse with the next pair in the stack, and the lower disk bends down on the opposite side to fuse with the disk below Shimoni et al.
This model contradicted the established helix model Paolillo, and has been much debated in the recent literature Brumfeld et al. The first cryo-ET study of vitreous chloroplast sections Daum et al.
In vitrified sections, which represent the native, undisturbed state of the thylakoid membrane, grana are seen as stacks of straight, exactly parallel membranes. Proteins with a twin arginine motif in their thylakoid signal peptide are shuttled through the Tat twin arginine translocation pathway, which requires a membrane-bound Tat complex and the pH gradient as an energy source. Some other proteins are inserted into the membrane via the SRP signal recognition particle pathway.
The chloroplast SRP can interact with its target proteins either post-translationally or co-translationally, thus transporting imported proteins as well as those that are translated inside the chloroplast.
Difference Between Grana and Thylakoid
Some transmembrane proteins may also spontaneously insert into the membrane from the stromal side without energy requirement. These include light-driven water oxidation and oxygen evolutionthe pumping of protons across the thylakoid membranes coupled with the electron transport chain of the photosystems and cytochrome complex, and ATP synthesis by the ATP synthase utilizing the generated proton gradient.
The water-splitting reaction occurs on the lumenal side of the thylakoid membrane and is driven by the light energy captured by the photosystems. This oxidation of water conveniently produces the waste product O2 that is vital for cellular respiration.
The molecular oxygen formed by the reaction is released into the atmosphere. Electron transport chains[ edit ] Two different variations of electron transport are used during photosynthesis: Cyclic electron transport or Cyclic photophosphorylation produces only ATP.
The noncyclic variety involves the participation of both photosystems, while the cyclic electron flow is dependent on only photosystem I.
In cyclic mode, the energized electron is passed down a chain that ultimately returns it in its base state to the chlorophyll that energized it. The carriers in the electron transport chain use some of the electron's energy to actively transport protons from the stroma to the lumen.
During photosynthesis, the lumen becomes acidicas low as pH 4, compared to pH 8 in the stroma. Source of proton gradient[ edit ] The protons in the lumen come from three primary sources. Photolysis by photosystem II oxidises water to oxygenprotons and electrons in the lumen. The transfer of electrons from photosystem II to plastoquinone during non-cyclic electron transport consumes two protons from the stroma.
These are released in the lumen when the reduced plastoquinol is oxidized by the cytochrome b6f protein complex on the lumen side of the thylakoid membrane. From the plastoquinone pool, electrons pass through the cytochrome b6f complex.
This integral membrane assembly resembles cytochrome bc1. The reduction of plastoquinone by ferredoxin during cyclic electron transport also transfers two protons from the stroma to the lumen. ATP generation[ edit ] The molecular mechanism of ATP Adenosine triphosphate generation in chloroplasts is similar to that in mitochondria and takes the required energy from the proton motive force PMF.
Connecting each granum by stromal thylakoids allow the functioning of all grana as a unit during photosynthesis.
The membranes of thylakoid and stromal thylakoid are responsible for the occurrence of light reaction of photosynthesis. The space between grana and inner membrane of the chloroplast is called stroma.
Dark reaction of the photosynthesis occurs in the stroma of chloroplast. A single chloroplast contains 10 to grana. Granum inside the chloroplast is shown in figure 1. Granum in Chloroplast What is Thylakoid Thylakoid is the little, round, flat, pillow-shaped things inside the chloroplast.
Thylakoid - Wikipedia
Thylakoid is a membrane-bound structure. The space between thylakoid membrane is called thylakoid lumen. The functional parts of the chloroplast are its membrane and the lumen.