Double membrane

Nucleus The nucleus is separated from the cytosol by a double membrane, the nuclear envelope. The DNA is complexed with basic proteins (histones) to form chromatin fibers, the material from which chromosomes are made. A distinct RNA-rich region, the nucleolus, is the site of ribosome assembly. The nucleus is the repository of genetic information encoded in DNA and organized into chromosomes. During mitosis, the chromosomes are replicated and transmitted to the daughter cells. The genetic information of DNA is transcribed into RNA in the nucleus and passes into the cytosol where it is translated into protein by ribosomes. 

Plant cells contain a unique family of organelles, the plastids, of which the chloroplast is the prominent example. Chloroplasts have a double membrane envelope, an inner volume called the stroma, and an internal membrane system rich in thylakoid membranes, which enclose a third compartment, the thylakoid lumen. Chloroplasts are significantly larger than mitochondria. Other plastids are found in specialized structures such as fruits, flower petals, and roots and have specialized roles. 

The photosynthetic apparatus in green plants and algae is located in the chloroplast, which is a flattened, double-membraned structure about 150-200 A thick/4,5 The two flat membranes lie one above the other and are united at their peripheries. These double-membraned structures have been termed thylakoids (from the Greek sacklike )/ Each membrane of the thylakoid consists of a water-insoluble lipoprotein complex which contains the light-absorbing chlorophyll and other pigments utilized in photosynthesis. 

Couto et al. [11] developed a flow injection system with potentiometric detection for determination of TC, OTC, and CTC in pharmaceutical products. A homogeneous crystalline CuS/Ag2S double membrane tubular electrode was used to monitor the Cu(II) decrease due to its complexation with OTC. The system allows OTC determination within a 49.1 1.9 x 103 ppm and a precision better than 0.4%. A flow injection method for the assay of OTC, TC, and CTC in pharmaceutical formulations was also developed by Wangfuengkanagul et al. [12] using electrochemical detection at anodized boron-doped diamond thin-film electrode. The detection limit was found to be 10 nM (signal-to-noise ratio = 3). 

Mitochondria are the centers for oxidative phosphorylation and the respiratory centers of all cells. While usually aerobic, some mitochondria (e.g. in some bacteria), are known that function anaerobically. These organelles occur ubiquitously in the neuron and its processes (Figs 1-4, 1-6). Their overall shape may change from one type of neuron to another but their basic morphology is identical to that in other cell types. Mitochondria consist morphologically of double-membraned sacs surrounded by protuberances, or cristae, extending from the inner membrane into the matrix space [7]. 

Before myelination the axon lies in an invagination of the Schwann cell (Fig. 4-10A). The plasmalemma of the cell then surrounds the axon and joins to form a double membrane structure that communicates with the cell surface. This structure, called the mesaxon, then elongates around the axon in a spiral fashion (Fig. 4-10). Thus, formation of myelin topologically resembles rolling up a sleeping bag the mesaxon winds about the axon, and the cytoplasmic surfaces condense into a compact myelin sheath and form the major dense line. The two external surfaces form the myelin intraperiod line. 

Mitochondria (45-56) are organelles possessing a double membrane, the inner of which is invaginated as cristae. An intermembrane space exists between the inner and outer membranes. The inner membrane consists of an unusually high amount of protein and possesses spherically shaped particles approx 9 nm in diameter. These particles appear to be equivalent to F0, Fb and adenosine triphosphatase. In contrast to the inner membrane, the outer membrane is smooth and appears to be connected to the smooth er. This membrane is permeable to all molecules of 10,000 Dalton or less. A mitochondrial matrix is enclosed by the inner membrane and consists of a ground substance of particles, nucleoids, ribosomes, and electron-transparent regions containing DNA. 

Mitochondria are found in the cell body and all processes of the neuron. They possess a double membrane and their own DNA and they play a role in cellular respiration and energy synthesis. Mitochondria contain enzymes essential for energy production in the form of adenosine triphosphate (ATP). 

Benchimol M, Durand R, Almeida JCA. 1997. A double membrane surrounds the hydrogenosomes of the anaerobic fungus Neocallimastix frontalis. FEMS Microbiol Lett 154 277-82. 

Material within the nucleus (nucleoplasm) is separated from the cytoplasm by the nuclear membrane (also known as an envelope), a double membrane that is continuous... 

The core of double membrane stirrer perfusion bioreactors is a stirrer on which two microporous hollow fiber membranes are mounted, one of them being hydrophobic and used for bubble-free aeration, the second of them being hydrophilic and used for cell-free medium exchange [15]. This system has been reported to provide viable cell densities of 20 million cells per miUiliter for more than two months [106]. Although Lehmann et al. [15] have described the scale-up of this system to the 20-L and 150-L scale, it has been most commonly employed at the bench-scale. 

A few years ago, genetic transformation of chloroplasts seemed impossible to achieve because of two significant challenges. First, the double membrane of chloroplasts offered a sigifificant barrier no viruses or bacteria were known to infect chloroplasts that could be used as vectors for... 

The final principal component of the cell is the nucleus. This is located in the center of the cell and is surrounded by a double membrane, the outer layer being derived from the ER of the cytoplasm and the inner layer coming from the nucleus itself. The two leaflets of the double membrane are fused in places, producing nuclear pores that enable the transfer of macromolecules from the cytoplasm to the nucleus. Two important components of the nucleus are chromatin and the nucleolus. Chromatin represents polymers of DNA complexed with protein. The nucleolus is a complex substructure, composed of ribonucleoprotein granules, that controls the synthesis of RNA destined to form the ribosomes of the cytoplasm. Cells engaged heavily in protein synthesis have... 

Acyl coenzyme As are introduced into mitochondria following coenzyme A esterification in the cytoplasm. Mitochondrial entry depends upon a double membrane transport involving carnitine acyltransferases II and I. Excess acetyl CoA is used for KB synthesis. KBs are transported in the blood and ultimately metabolized via the Krebs cycle. KBs are necessary to provide energy to the brain during fasting, a true alternative substrate to glucose. 

All hydrogenosomes and mitosomes examined to date appear to have double membranes, which implies the presence of an intermembrane space. 

Fig. 2 Routine preparation of a hydrogenosome (H) in Trichomonas vaginalis (a), Tri-trichomonas foetus (b), and Monocercomonas sp. (c). Note that in T. foetus the hydrogenosome is spherical, enveloped by a double membrane (arrows), and presents a single peripheral vesicle, whereas in T vaginalis several peripheral vesicles are seen surrounding the organelle (arrows) and in Monocercomonas the hydrogenosome is very elongated. ER, endoplasmic reticulum N, nucleus. Bars = 100 nm. (From Benchimol 2001 Diniz and Benchimol 1998)...

Fig. 4 Thin sections of the fungal hydrogenosome (H) from Neocallimastix frontalis. In a there is one hydrogenosome in the process of division and the inner hydrogenosomal membrane is in process of septum formation. Note that there is another hydrogenosome with a double membrane, which is not in process of division. In b all the hydrogenosomes are dividing, presenting internal septa. Bars = 100 nm. (From Benchimol et al. 1997)...

Fig. 5 Thin sections of a I foetus (a) and a fungal (b) hydrogenosome (H) from Neo-callimastix frontalis. Both hydrogenosomes are clearly enveloped by a double membrane (arrow in (a), arrowheads in (b)). Invaginations of the hydrogenosome membrane were occasionally observed (arrow in (a)). The black spot in (a) is a calcium deposit in the peripheral vesicle (asterisks). CW, cell wall. Bars = 100 nm. (Fig. 5a from Benchimol, unpublished Fig. 5b, from Benchimol et al. 1997)...

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