Chloroplast membrane: Difference between revisions
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{{Cell biology|chloroplast=yes}} |
{{Cell biology|chloroplast=yes}} |
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[[Chloroplast]]s contain several important [[biological membrane|membranes]], vital for their function. Like [[mitochondria]], chloroplasts have a double-membrane envelope, called the '''chloroplast envelope''', but unlike [[mitochondria]], chloroplasts also have internal membrane structures called '''[[thylakoid]]s'''. Furthermore, one or two additional membranes may enclose chloroplasts in organisms that underwent [[secondary endosymbiosis]], such as the [[euglenid]]s and [[chlorarachniophyte]]s.<ref>Kim, E., and Archibald, J. M. (2009) "Diversity and Evolution of Plastids and Their Genomes". In ''The Chloroplast'', Anna Stina Sandelius and Henrik Aronsson (eds.), 1–39. Plant Cell Monographs 13. Springer Berlin Heidelberg. {{doi|10.1007/978-3-540-68696-5_1}} {{ISBN|978-3-540-68696-5}}</ref> |
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The |
The chloroplasts come via [[endosymbiosis]] by engulfment of a photosynthetic cyanobacterium by the eukaryotic, already mitochondriate cell.<ref>{{cite journal|last1=Ochoa de Alda|first1=Jesús A. G.|last2=Esteban|first2=Rocío|last3=Diago|first3=María Luz|last4=Houmard|first4=Jean|title=The plastid ancestor originated among one of the major cyanobacterial lineages|journal=Nature Communications|date=15 September 2014|volume=5|pages=4937|doi=10.1038/ncomms5937|pmid=25222494|bibcode=2014NatCo...5.4937O |doi-access=free}}</ref> Over millions of years the endosymbiotic cyanobacterium evolved structurally and functionally, retaining its own DNA and the ability to divide by binary fission (not mitotically) but giving up its autonomy by the transfer of some of its genes to the nuclear genome. |
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==Envelope membranes== |
==Envelope membranes== |
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Each of the envelope membranes is a [[lipid bilayer]] that is between 6 and 8 [[nanometre|nm]] thick. The lipid composition of the outer membrane has been found to be 48% [[phospholipid]]s, 46% [[galactolipid]]s and |
Each of the envelope membranes is a [[lipid bilayer]] that is between 6 and 8 [[nanometre|nm]] thick. The lipid composition of the outer membrane has been found to be 48% [[phospholipid]]s, 46% [[galactolipid]]s and 7% [[sulfolipid]]s, while the inner membrane has been found to contain 16% [[phospholipid]]s, 79% [[galactolipid]]s and 5% [[sulfolipid]]s in spinach chloroplasts.<ref name=Block1983>{{cite journal|last=Block|first=MA|author2=Dorne, AJ |author3=Joyard, J |author4= Douce, R |title=Preparation and characterization of membrane fractions enriched in outer and inner envelope membranes from spinach chloroplasts. II. Biochemical characterization|journal=The Journal of Biological Chemistry|date=Nov 10, 1983|volume=258|issue=21|pages=13281–6|doi=10.1016/S0021-9258(17)44113-5 |pmid=6630230|doi-access=free }}</ref> |
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The outer membrane is permeable to most [[ions]] and [[metabolite]]s, but the |
The outer membrane is permeable to most [[ions]] and [[metabolite]]s, but the inner membrane of the chloroplast is highly specialised with [[transport protein]]s.<ref>{{cite journal|last=Heldt|first=HW|author2=Sauer, F |title=The inner membrane of the chloroplast envelope as the site of specific metabolite transport.|journal=Biochimica et Biophysica Acta (BBA) - Bioenergetics|date=Apr 6, 1971|volume=234|issue=1|pages=83–91|pmid=5560365|doi=10.1016/0005-2728(71)90133-2}}</ref><ref>{{cite journal|last=Inoue|first=Kentaro|title=The Chloroplast Outer Envelope Membrane: The Edge of Light and Excitement|journal=Journal of Integrative Plant Biology|date=1 August 2007|volume=49|issue=8|pages=1100–1111|doi=10.1111/j.1672-9072.2007.00543.x|doi-access=free}}</ref> For example, carbohydrates are transported across the inner envelope membrane by a [[triose phosphate translocator]].<ref>{{cite journal|last1=Walters|first1=R. G.|title=A Mutant of Arabidopsis Lacking the Triose-Phosphate/Phosphate Translocator Reveals Metabolic Regulation of Starch Breakdown in the Light|journal=Plant Physiology|year=2004|volume=135|issue=2|pages=891–906|doi=10.1104/pp.104.040469|pmid=15173568|first2=DG|last3=Horton|first3=P|last4=Kruger|first4=NJ|pmc=514124|last2=Ibrahim}}</ref> The two envelope membranes are separated by a gap of 10–20 nm, called the [[intermembrane space]]. |
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==Thylakoid membrane== |
==Thylakoid membrane== |
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Within the envelope membranes, in the region called the [[stroma (fluid)|stroma]], there is a system of interconnecting flattened membrane compartments, called the '''[[thylakoid]]s'''. The '''thylakoid membrane''' is quite similar in lipid composition to the inner envelope membrane, containing 78% [[galactolipid]]s, 15.5% [[phospholipid]]s and 6.5% [[sulfolipid]]s in spinach chloroplasts.<ref name=Block1983 /> The thylakoid membrane encloses a single, continuous aqueous compartment called the '''[[thylakoid lumen]]'''.<ref>{{cite journal|last=Mustárdy|first=L| |
Within the envelope membranes, in the region called the [[stroma (fluid)|stroma]], there is a system of interconnecting flattened membrane compartments, called the '''[[thylakoid]]s'''. The '''thylakoid membrane''' is quite similar in lipid composition to the inner envelope membrane, containing 78% [[galactolipid]]s, 15.5% [[phospholipid]]s and 6.5% [[sulfolipid]]s in spinach chloroplasts.<ref name=Block1983 /> The thylakoid membrane encloses a single, continuous aqueous compartment called the '''[[thylakoid lumen]]'''.<ref>{{cite journal|last=Mustárdy|first=L|author2=Garab, G |title=Granum revisited. A three-dimensional model—where things fall into place|journal=Trends in Plant Science|date=March 2003|volume=8|issue=3|pages=117–22|pmid=12663221|doi=10.1016/S1360-1385(03)00015-3}}</ref> |
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These are the sites of light absorption and [[Adenosine triphosphate|ATP]] synthesis, and contain many proteins, including those involved in the [[electron transport chain]]. Photosynthetic pigments such as chlorophylls a,b and |
These are the sites of light absorption and [[Adenosine triphosphate|ATP]] synthesis, and contain many proteins, including those involved in the [[electron transport chain]]. Photosynthetic pigments such as chlorophylls a,b,c and some others, e.g., xanthophylls, carotenoids, phycobilins are also embedded within the granum membrane. With exception of chlorophyll a, all the other associated pigments are "accessory" and transfer energy to the reaction centers of Photosytems I and II. |
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The membranes of the thylakoid contain photosystems I and II which harvest solar energy to excite electrons which travel down the [[electron transport chain]]. This exergonic fall in potential energy along the way is used to draw (not pump!) H<sup>+</sup> ions from the lumen of the thylakoid into the cytosol of a [[cyanobacterium]] or the stroma of a chloroplast. A steep H<sup>+</sup> gradient is formed, which allows [[chemiosmosis]] to occur, where the thylakoid, |
The membranes of the thylakoid contain photosystems I and II which harvest solar energy to excite electrons which travel down the [[electron transport chain]]. This exergonic fall in potential energy along the way is used to draw (not pump!) H<sup>+</sup> ions from the lumen of the thylakoid into the cytosol of a [[cyanobacterium]] or the stroma of a chloroplast. A steep H<sup>+</sup> gradient is formed, which allows [[chemiosmosis]] to occur, where the thylakoid, transmembrane ATP-synthase serves a dual function as a "gate" or channel for H<sup>+</sup> ions and a catalytic site for the formation of ATP from ADP + a PO<sub>4</sub><sup>3−</sup> ion. |
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Experiments have shown that the pH within the stroma is about 7.8, while that of the lumen of the thylakoid is 5. This corresponds to a six-hundredfold difference in concentration of H<sup>+</sup> ions. The H<sup>+</sup> ions pass down through the ATP-synthase catalytic gate. This chemiosmotic phenomenon occurs in mitochondria. |
Experiments have shown that the pH within the stroma is about 7.8, while that of the lumen of the thylakoid is 5. This corresponds to a six-hundredfold difference in concentration of H<sup>+</sup> ions. The H<sup>+</sup> ions pass down through the ATP-synthase catalytic gate. This chemiosmotic phenomenon also occurs in mitochondria. |
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==Lipid organization in thylakoid membranes== |
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The most abundant lipid in chloroplast thylakoid membranes is monogalactosyl diglyceride (MGDG) and this lipid forms reverse hexagonal cylindrical phase (H-II) in aqueous dispersions. Thus, it is a pertinent question if thylakoid membranes have a lipid bilayer organization. Total lipid extract of thylakoid membranes, which includes chlorophyls and pigments, does form multibilayer liposomal structures (Figure 1) in aqueous dispersions. However, in thylakoid membranes, chlorophyll is a part of protein complexes, known as light harvesting complexes. This enquiry was addressed by studying the dynamic organization of lipids in chloroplast thylakoid membranes by [[carbon-13 NMR]] and [[spin label]] [[electron spin resonance]] spectroscopy. A matching pattern of membrane bilayer fluidity gradient in both native thylakoid membranes and liposomal preparations prepared from their total lipid extract (Figure 2) vouches for existence of largely a lipid bilayer organization in spinach chloroplast thylakoid membranes.Figure 2 shows variation of central linewidth (Wo) in Gauss of [[electron spin resonance]] or ESR spectra of spin labeled positions 5,7,9,12,13,14 and 16th carbon, with respect to carbonyl-group 1st-carbon of stearic acid spin label (SASL) probe molecule, incorporated (one label in each sample) in native thylakoid membranes (triangles) and multilamellar liposomes (circles), prepared from aqueous dispersions of total lipid extract of these membranes, as a function of position of spin label moiety. Reduction in Wo, means increase in segmental motion of probe and increase in fluidity in that local micro-environment of lipid organization. Almost parallel graphs of ESR central linewidths (Wo) with positions 9-16 of signal-producing doxyl-moiety in SASL probes, indicates similar dynamic lipid organization in the two membrane systems.http://www.researchgate.net/publication/225688482_Magnetic_resonance_studies_of_dynamic_organisation_of_lipids_in_chloroplast_membranes?ev=prf_pub<ref>YashRoy R C (1990) Magnetic resonance studies of the dynamic organization of chloroplast membranes. ''Journal of Biosciences'' vol. 15(4), pp. 281-288.http://www.researchgate.net/publication225688482_Magnetic_resonance_studies_of_dynamic_organisation_of_lipids_in_chloroplast_membranes?ev=prf_pub</ref>. |
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Figure 2 shows variation of central linewidth (Wo) in Gauss of [[electron spin resonance]] or ESR spectra of spin labeled positions 5,7,9,12,13,14 and 16th carbon, with respect to carbonyl-group 1st-carbon of stearic acid spin label (SASL) probe molecule, incorporated (one label in each sample) in native thylakoid membranes (triangles) and multilamellar liposomes (circles), prepared from aqueous dispersions of total lipid extract of these membranes, as a function of position of spin label moiety. Reduction in Wo, means increase in segmental motion of probe and increase in fluidity in that local micro-environment of lipid organization. Almost parallel graphs of ESR central linewidths (Wo) with positions 9-16 of signal-producing doxyl-moiety in SASL probes, indicates similar dynamic lipid organization in the two membrane systems. |
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[[File:Liposomes_made_from_aqueous_dispersions_of_total_lipid-extract_of_spinach_thylakoid_membranes_by_PTA_negative_staining_TEM._%28YashRoy_R_C_1990,_J_Biosciences,_15,_281-287.%29.jpg|thumb|Figure 1 Multi-bilayer organization of aqueous lipid dispersions of total lipid extract of spinach thylakoid membranes]] |
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[[File:Fluidity_or_flexibility_gradient_in_spinach_thylakoid_membranes_and_extracted_aqueous_lipid_dispersions_by_stearic_acid_spin_label_electron_spin_resonance._%28YashRoy_R_C_1990,_J_Biosciences,_vol_15,_pp_281-287..jpg|thumb|Figure 2 Fluidity gradient of native thylakoid membranes (triangles) and multi-bilayer liposomes (circles) made from total lipids extracted from thylakoid membranes]] |
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==References== |
==References== |
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{{Reflist}} |
{{Reflist}} |
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==See also== |
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*[[TIC/TOC complex]] |
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{{DEFAULTSORT:Chloroplast Membrane}} |
{{DEFAULTSORT:Chloroplast Membrane}} |
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Latest revision as of 03:07, 28 November 2023
| Cell biology | |
|---|---|
| Chloroplast | |
 Components of a typical chloroplast
1 Granum
4 Stromal thylakoid |
Chloroplasts contain several important membranes, vital for their function. Like mitochondria, chloroplasts have a double-membrane envelope, called the chloroplast envelope, but unlike mitochondria, chloroplasts also have internal membrane structures called thylakoids. Furthermore, one or two additional membranes may enclose chloroplasts in organisms that underwent secondary endosymbiosis, such as the euglenids and chlorarachniophytes.[1]
The chloroplasts come via endosymbiosis by engulfment of a photosynthetic cyanobacterium by the eukaryotic, already mitochondriate cell.[2] Over millions of years the endosymbiotic cyanobacterium evolved structurally and functionally, retaining its own DNA and the ability to divide by binary fission (not mitotically) but giving up its autonomy by the transfer of some of its genes to the nuclear genome.
Envelope membranes
[edit]Each of the envelope membranes is a lipid bilayer that is between 6 and 8 nm thick. The lipid composition of the outer membrane has been found to be 48% phospholipids, 46% galactolipids and 7% sulfolipids, while the inner membrane has been found to contain 16% phospholipids, 79% galactolipids and 5% sulfolipids in spinach chloroplasts.[3]
The outer membrane is permeable to most ions and metabolites, but the inner membrane of the chloroplast is highly specialised with transport proteins.[4][5] For example, carbohydrates are transported across the inner envelope membrane by a triose phosphate translocator.[6] The two envelope membranes are separated by a gap of 10–20 nm, called the intermembrane space.
Thylakoid membrane
[edit]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 thylakoid membrane encloses a single, continuous aqueous compartment called the thylakoid lumen.[7]
These are the sites of light absorption and ATP synthesis, and contain many proteins, including those involved in the electron transport chain. Photosynthetic pigments such as chlorophylls a,b,c and some others, e.g., xanthophylls, carotenoids, phycobilins are also embedded within the granum membrane. With exception of chlorophyll a, all the other associated pigments are "accessory" and transfer energy to the reaction centers of Photosytems I and II.
The membranes of the thylakoid contain photosystems I and II which harvest solar energy to excite electrons which travel down the electron transport chain. This exergonic fall in potential energy along the way is used to draw (not pump!) H+ ions from the lumen of the thylakoid into the cytosol of a cyanobacterium or the stroma of a chloroplast. A steep H+ gradient is formed, which allows chemiosmosis to occur, where the thylakoid, transmembrane ATP-synthase serves a dual function as a "gate" or channel for H+ ions and a catalytic site for the formation of ATP from ADP + a PO43− ion.
Experiments have shown that the pH within the stroma is about 7.8, while that of the lumen of the thylakoid is 5. This corresponds to a six-hundredfold difference in concentration of H+ ions. The H+ ions pass down through the ATP-synthase catalytic gate. This chemiosmotic phenomenon also occurs in mitochondria.
References
[edit]- ^ Kim, E., and Archibald, J. M. (2009) "Diversity and Evolution of Plastids and Their Genomes". In The Chloroplast, Anna Stina Sandelius and Henrik Aronsson (eds.), 1–39. Plant Cell Monographs 13. Springer Berlin Heidelberg. doi:10.1007/978-3-540-68696-5_1 ISBN 978-3-540-68696-5
- ^ Ochoa de Alda, Jesús A. G.; Esteban, Rocío; Diago, María Luz; Houmard, Jean (15 September 2014). "The plastid ancestor originated among one of the major cyanobacterial lineages". Nature Communications. 5: 4937. Bibcode:2014NatCo...5.4937O. doi:10.1038/ncomms5937. PMID 25222494.
- ^ a b Block, MA; Dorne, AJ; Joyard, J; Douce, R (Nov 10, 1983). "Preparation and characterization of membrane fractions enriched in outer and inner envelope membranes from spinach chloroplasts. II. Biochemical characterization". The Journal of Biological Chemistry. 258 (21): 13281–6. doi:10.1016/S0021-9258(17)44113-5. PMID 6630230.
- ^ Heldt, HW; Sauer, F (Apr 6, 1971). "The inner membrane of the chloroplast envelope as the site of specific metabolite transport". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 234 (1): 83–91. doi:10.1016/0005-2728(71)90133-2. PMID 5560365.
- ^ Inoue, Kentaro (1 August 2007). "The Chloroplast Outer Envelope Membrane: The Edge of Light and Excitement". Journal of Integrative Plant Biology. 49 (8): 1100–1111. doi:10.1111/j.1672-9072.2007.00543.x.
- ^ Walters, R. G.; Ibrahim, DG; Horton, P; Kruger, NJ (2004). "A Mutant of Arabidopsis Lacking the Triose-Phosphate/Phosphate Translocator Reveals Metabolic Regulation of Starch Breakdown in the Light". Plant Physiology. 135 (2): 891–906. doi:10.1104/pp.104.040469. PMC 514124. PMID 15173568.
- ^ Mustárdy, L; Garab, G (March 2003). "Granum revisited. A three-dimensional model—where things fall into place". Trends in Plant Science. 8 (3): 117–22. doi:10.1016/S1360-1385(03)00015-3. PMID 12663221.