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The thylakoid lumen is a membrane-enclosed aqueous compartment. Growing evidence indicates that the thylakoid lumen is not only a sink for protons and inorganic ions translocated during photosynthetic reactions but also a place for metabolic activities, e.g. proteolysis of photodamaged proteins, to sustain efficient photosynthesis. However, the mechanism whereby organic molecules move across the thylakoid membranes to sustain these lumenal activities is not well understood. In a recent study of Cyanophora paradoxa chloroplasts [muroplasts], we fortuitously detected a conspicuous diffusion channel activity in the thylakoid membranes. Here, using proteoliposomes reconstituted with the thylakoid membranes from muroplasts and from two other phylogenetically distinct organisms, cyanobacterium Synechocystis sp. PCC 6803 and spinach, we demonstrated the existence of nonselective channels large enough for enabling permeation of small organic compounds [e.g. carbohydrates and amino acids with Mr < 1500] in the thylakoid membranes. Moreover, we purified, identified, and characterized a muroplast channel named here CpTPOR. Osmotic swelling experiments revealed that CpTPOR forms a nonselective pore with an estimated radius of ∼1.3 nm. A lipid bilayer experiment showed variable-conductance channel activity with a typical single-channel conductance of 1.8 nS in 1 m KCl with infrequent closing transitions. The CpTPOR amino acid sequence was moderately similar to that of a voltage-dependent anion-selective channel of the mitochondrial outer membrane, although CpTPOR exhibited no obvious selectivity for anions and no voltage-dependent gating. We propose that transmembrane diffusion pathways are ubiquitous in the thylakoid membranes, presumably enabling rapid transfer of various metabolites between the lumen and stroma.
chloroplast
cyanobacteria
membrane transport
permeability
liposome
photosynthesis
CpTPOR
diffusion channel
muroplast
porin
thylakoid membrane
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© 2018 Kojima et al.
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Selina Solutions Class 6 Biology Solutions for Exercise Short Answer Questions [SA] in Chapter 3 - Cell - The Structure and Function
Question 4 Short Answer Questions [SA]
Q4] The cell membrane is called selectively permeable. Why ?
Answer:
Solution :
The cell membrane is a very thin layer of protein and fat. It allows only selective substances to pass through it, hence,it is called a selectively permeable membrane.
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"Hello friends welcome leaders online cookbook solving session in desktop point at the first question the question says the cell membrane is called selectively of Liquid Fire now friends in this question. We have tell us the reason why the cell membrane is called a selectively permeable. Let's look at the self inflate first. First is the snail temperate at this of the part allow the entry and exist of the substance. The cell membrane is very thin. I'm just still nail is basically made up of protein. And act which allows the entry and exit of the substance. Don't add this process. It will allow only selective. Substance to pass through it. And as it allow only selectively substance to pass the word. It is called as selectively permeable membrane as only selectively substance are getting penetrated inside at this pair are getting the entry inside at this bite is pollock select the copy of the so this is how we approach this question. If you have any questions drop a comment below and subscribe Battle for regular updates and cue Thank you."
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