Thylakoid - Wikipedia
The details of the 3D arrangement of grana and stroma thylakoids in chloroplasts the relationship between cellular structure and function in these cyanobacteria. . Mark Ellisman, and Alice Dohnalkova for discussions and helpful advice. What is the difference between a Lamellae and a thylakoid?? Thanks Posted from Soo the thylakoids are the disc-like structures, a stack of them is a grana. Grana and stroma thylakoid contains fluorescent chlorophyll. Shiell BJ, Venema JH, Vredenberg WJ, Mostowska A, Garstka M: Correlation. between anti-oxidant nanoparticle carried drug in cancer therapy and surface.
The three-dimensional reconstruction uncovered the fine thylakoid membrane structure in live cells. The time-lapse imaging shows that the entire thylakoid membrane network is structurally stable, but the individual thylakoid membrane structure is flexible in vivo. Our observation indicates that grana serve as a framework to maintain structural integrity of the entire thylakoid membrane network. Both the structural stability and flexibility of thylakoid membranes would be essential for dynamic protein reorganization under fluctuating light environments.
Photosynthetic organisms have developed flexible machinery for effective light energy use 12. In higher plants, cyclic electron transport is stimulated by the association of chloroplast NADH dehydrogenase-like complex with PSI When PSII is damaged, disassembly of PSII occurs after its migration from the stacked, appressed membranes, or grana, to the single-layer, stroma-exposed membranes, or stroma lamellae, where PSII subunits are replaced 20 Based on these facts, the structure and arrangement of thylakoid membranes have to be flexible for such protein reorganization to be taken place in response to changing light environments.
The structure and arrangement of thylakoid membranes have long been studied since the first observation using light microscopy by Hugo von Mohl in The grana inside chloroplasts are already identified by light microscopy as dense, dot-like structures Introducing electron microscopy has deepened our understanding of the structural complexity of thylakoid membranes, showing the remarkable architecture in which stroma lamellae connect to grana in the helical configuration 232425 Recently, electron tomography has determined the three-dimensional 3D structure of thylakoid membranes in higher plants 2728revealing the distinctive image of the junctional connections between grana and stroma lamellae.
Difference Between Grana and Thylakoid | Definition, Function, Relationship
Intriguingly, the junctional slits where stroma lamellae connect grana show significant structural variations 2728reflecting the variability of the membrane structure. The space between thylakoid membrane is called thylakoid lumen. The functional parts of the chloroplast are its membrane and the lumen. The light-trapping green pigment, chlorophyll is found in the thylakoid membrane, held by the membrane proteins. Chlorophylls are organized into photosystem 1 and photosystem 2 on the thylakoid membrane.
The light energy of the sunlight is converted into electrical energy by chlorophyll. The electrical energy in the form of high energy electrons is passed through membrane proteins from one to another, providing the power to pump protons from stroma into thylakoid lumen.
Lamellae and Thylakoids??? - The Student Room
When these pumped proteins are rushed back into the stroma, energy is released, which is readily used by the enzyme, ATP synthase by synthesizing ATP. Membrane proteins in the thylakoid are shown in figure 2.
Grana are the stacks of thylakoids inside the chloroplast. Thylakoid is the pillow-shaped compartments in the chloroplast. It is integrated into the thylakoid membrane with the CF1-part sticking into stroma.
- Visualizing structural dynamics of thylakoid membranes
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.
How are chloroplasts adapted to their function?
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.
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: An N-terminal chloroplast targeting peptide shown in yellow in the figurefollowed by a thylakoid targeting peptide shown in blue. Proteins are imported through the translocon of outer and inner membrane Toc and Tic complexes.
After entering the chloroplast, the first targeting peptide is cleaved off by a protease processing imported proteins.
Difference Between Grana and Thylakoid
This unmasks the second targeting signal and the protein is exported from the stroma into the thylakoid in a second targeting step. This second step requires the action of protein translocation components of the thylakoids and is energy-dependent. Proteins are inserted into the membrane via the SRP-dependent pathway 1the Tat-dependent pathway 2or spontaneously via their transmembrane domains not shown in figure.
Lumenal proteins are exported across the thylakoid membrane into the lumen by either the Tat-dependent pathway 2 or the Sec-dependent pathway 3 and released by cleavage from the thylakoid targeting signal.
The different pathways utilize different signals and energy sources. The Sec secretory pathway requires ATP as energy source and consists of SecA, which binds to the imported protein and a Sec membrane complex to shuttle the protein across.