Granum | plant anatomy | guiadeayuntamientos.info
The organization and inter-relationships of the membranes of .. drion; w, cell wall; pe, plastid envelope; sr, stroma; g, granum; s, starch. X c. 44, granum. Granum: chloroplast: Characteristics of chloroplasts: tight stacks called grana ( singular granum). Grana are connected by stromal lamellae, extensions that run . A granum is a stack of thylakoids in the chloroplast. The stroma is the gel-like material that surrounds the grana inside the chloroplast.
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.
Difference Between Grana and Stroma
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.Structure of chloroplast,thylakoid,granum,stroma,light reaction,dark reaction,cell,chlorophyll,phyto
After entering the chloroplast, the first targeting peptide is cleaved off by a protease processing imported proteins. This unmasks the second targeting signal and the protein is exported from the stroma into the thylakoid in a second targeting step.
What is the relationship between the granum and the stroma?
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. 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. 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. 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. Chlorophyll and other photosynthetic pigments are held by membrane proteins on the surface of the thylakoid.
Difference Between Grana and Stroma | Definition, Structure, Function
They are organized into photosystem 1 and 2 on the thylakoid membrane. What is Stroma Stroma refers to a colorless jell-like matrix of the chloroplast in which the dark reaction of photosynthesis takes place. Enzymes required for the dark reaction are embedded in the stroma. Stroma surrounds the grana. In the stroma, carbon dioxide and water are used in the production of simple carbohydrates by using the light energy trapped by light reaction.
Stroma and grana of a chloroplast are shown in figure 2. Structure of a Chloroplast Dark reaction of photosynthesis is also called the Calvin cycle. The three stages of the Calvin cycle are carbon fixation, reduction reactions, and RuBP regeneration. Similarities Between Grana and Stroma Both grana and stroma are two structures of the chloroplast.