While gendered sexual scripts are hegemonic at the cultural level, research suggests they may be less so at dyadic and individual levels.
Testosterone is thought to play a crucial role in mediating sexual differentiation of brain structures. Examinations of the cognitive effects of testosterone have also shown beneficial and potentially sex-specific effects on executive function and mnemonic processes. Yet these findings remain limited by an incomplete understanding of the critical timing and brain regions most affected by testosterone, the lack of documented links between testosterone-related structural brain changes and cognition, and the difficulty in distinguishing the effects of testosterone from those of related sex steroids such as of estradiol and dehydroepiandrosterone DHEA. We found prefrontal-hippocampal covariance to vary as a function of testosterone levels, but only in boys. Boys also showed a specific association between positive prefrontal-hippocampal covariance as seen at higher testosterone levels and lower performance on specific components of executive function monitoring the action process and flexibly shifting between actions.
David C. Mitochondria are vital organelles that perform a variety of fundamental functions ranging from the synthesis of ATP through to being intimately involved in programmed cell death. Comprised of at least six compartments: outer membrane, inner boundary membrane, intermembrane space, cristal membranes, intracristal space, and matrix, mitochondria have a complex, dynamic internal structure. This internal dynamism is reflected in the pleomorphy and motility of mitochondria. Mitochondria contain their own DNA mtDNAencoding a small of vital genes, but this role as a genetic vault is not compatible with the role of mitochondria in bioenergetics since electron transport in the generation of reactive oxygen species ROS that induce lesions in the mtDNA.
It is hypothesized that ROS shape the morphological organization of the higher plant cell mitochondrial population into a discontinuous wholeand that ROS are a selective pressure affecting the organization of the mitochondrial genome.
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This review describes how inter- and intra-mitochondrial compartmentalization underpins the biology of this complex organelle. Mitochondria are highly dynamic, pleomorphic organelles composed of a smooth outer membrane surrounding an inner membrane of ificantly larger surface area that, in turn, surrounds a protein-rich core, the matrix.
Although mitochondria contain their own genome and protein-synthesizing machinery Leaver et al.
The role of the mitochondrion in the synthesis of ATP formed by oxidative phosphorylation is well established Saraste, and, in addition, mitochondria are involved in numerous other metabolic processes including the biosynthesis of amino acids, vitamin cofactors, fatty acids, and iron-sulphur clusters Mackenzie and McIntosh, ; Bowsher and Tobin, Apart from the role of the mitochondrion in ATP synthesis and various biosynthetic pathways the mitochondrion is one of three cell compartments involved in photorespiration Douce and Neuburger,is implicated in cell alling Vandecasteele et al.
This review deals with the complex biology of the mitochondrion and describes how various levels of compartmentalization within the mitochondrion and cellular mitochondrial population as a whole the chondriome underpin the multiple functions of this vital organelle.
Although focused on the higher plant mitochondrial compartment, frequent reference will be made to studies using non-plant model organisms. In some cases, this is simply due to a paucity of information about specific aspects of plant mitochondrial biology; in all cases it is because I believe the information is of fundamental relevance. A short article such as this can only provide a brief overview of the importance of compartmentalization to the life of the mitochondrion.
A great deal has been left out e.
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The vast majority of biological energy ATP production is associated with energy-transducing membranes: the prokaryotic plasma membrane of bacteria and blue-green algae, the thylakoid membranes of chloroplasts, and the inner mitochondrial membrane. The energy-transducing membrane is central to the chemiosmotic theory that explains the basic mechanism of biological energy production, whereby ATP production is coupled to the controlled dissipation of a proton electrochemical gradient proton motive force.
The membrane allows compartmentalization of protons, via their vectorial transport across the membrane, by the action of a primary proton pump s. Any proton leak across the membrane would cause a short-circuit, destroy the compartmentalization of protons and uncouple the proton motive force from the ATP synthase. The energy-transducing membrane must, therefore, be essentially closed and have a high resistance to proton flux. The energy-transducing membrane of mitochondria, the inner mitochondrial membrane, is a highly pleomorphic structure.
Although there are an almost endless variety of inner mitochondrial membrane morphologies in mitochondria from different species, from different cell types within the same species or from the same cell types but in different metabolic states Munn,some generalizations can be made. Transmission electron microscopy led to the development of models of the internal structure of mitochondria.
Palade's model Palade,also called the baffle model, depicted the invaginations of the inner mitochondrial membrane, the cristae, as random, wide in-folds of the membrane the typical text book image, Fig. It is clear from two ground-breaking research papers published in Lea et al.
Models of mitochondrial membrane structures.
This model originated with Palade in the s and has been prominent until recently. Electron tomography has been instrumental in providing the improved 3D visualizations of mitochondria in situ that have generated a new model for membrane architecture. Instead of the large openings connecting the intercristal space to the intermembrane space present in the baffle model, narrow tubular openings crista junctions connect these spaces in this model.
Most cristae have more than one crista junction and these can be arranged on the same side of the mitochondrial periphery, or on opposite sides if the crista extends completely across the matrix. Reprinted from Perkins and Frey Copyrightwith permission from Elsevier.
Additional annotations in b by the author. The obtained using advanced tomographic alabama techniques demonstrate that, at least in animal tissue, tubular rather than lamellar cristae predominate and that the morphology of cristae infers that they Logan structurally distinct from the rest of the inner mitochondrial membrane. An additional finding was confirmation that the cristae were connected to the inner boundary membrane cortical inner mitochondrial membrane, parallel to the outer membrane by membranous tubules, instead of the cristae being discreet in-folds of the membrane as suggested by Palade Daems and Wisse first reported that cristae attach to the inner boundary membrane via narrow tubules termed pediculi, but this finding was not consistent with the baffle paradigm.
Subsequently, it has been shown that the connections between the cristae and the inner boundary membrane, the term crista junction has superseded pediculi, have a preferred size and morphology and are independent of the source of the mitochondrion and the means of fixation Mannella et al. Indeed, it has been proposed that crista networks are a uniform structural component of all mitochondria Perkins and Frey, For example, in rat liver mitochondria, crista junctions are 30—50 nm alabama although tubules three Logan that length have been measured, and in Neurospora crassa the slot-like crista junctions have been measured at up to nm, although the average length is 30—40 nm Frey et al.
The of crista junctions and the morphology of the intercristal space have been shown to change with the metabolic state of the mitochondria Hackenbrock, ; Mannella et al. In the orthodox state, corresponding to network matrix expansion, the intercristal space is compressed and tubular with few cristae interconnections and one or two crista junctions with the inner boundary membrane.
In the condensed state, corresponding to partial matrix contraction, the intercristal spaces are dilated and there are more numerous intercristal membrane connections and crista junctions. Hackenbrock demonstrated, by rapid fixation of purified mouse liver mitochondria in different respiratory steady-states, that mitochondria in state 3 maximum respiratory rate in the presence of excess ADP and respiratory substrate were in the condensed conformation, but reverted to an orthodox morphology after entering state 4 respiration characterized by a reduction in respiration due to the depletion of ADP.
Addition of ADP to these mitochondria caused a reversion to the condensed form within 35 s, followed by a gradual return to the orthodox conformation as all the ADP is phosphorylated. Dry, quiescent maize embryos contain mitochondria with little internal membrane structure and an electron-light matrix Logan et al. Upon imbibition, mitochondrial biogenesis is stimulated and within 24 h protrusion of the radicle typically took place after 36—48 h imbibition mitochondria in the embryo have a normal, orthodox, conformation Fig.
By contrast, mitochondria isolated from germinated embryos after 48 h imbibition had a condensed conformation Fig. It is tempting to speculate that the switch sex an orthodox to a condensed conformation during mitochondrial biogenesis is indicative of the changing biochemistry of the organelle as it switches from discreet reliant on the provision of sex from external NADH dehydrogenases to the newly assembled TCA cycle Logan et al.
Conformation of internal structure in mitochondrial purified from germinating maize embryos. Transmission electron micrographs of mitochondria after subcellular fractionation of embryos excised from seed imbibed for either a 24 h, orthodox conformation or b 48 h, condensed conformation. A condensed morphology, large intercristal spaces with narrow crista junctions to the intermembrane space, has been shown by computer simulation to lead to a reduction in diffusion of ADP into the cristae, reduction in the transport of ADP across the inner mitochondrial membrane and, therefore, ATP production Mannella, Adoption of an orthodox confirmation when the bulk ADP concentration is low might therefore act to minimize the negative effect on ATP production of limited diffusion of ADP through the crista junctions by concentrating the ADP within a smaller intercristal volume.
The of Hackenbrock and those from the computer simulation suggest that inner mitochondrial membrane remodelling, which affects the degree of compartmentalization, is a mechanism enabling the control of ATP production by mediating ADP availability Mannella, Whether this control mechanism operates in vivo remains to be determined.
Sex-specific associations of testosterone with prefrontal-hippocampal development and executive function
What is clear from the above discussion is that at least six discrete mitochondrial compartments can be recognized on a structural basis: outer membrane, intermembrane space, inner boundary membrane, cristal membrane, intercristal space, and matrix. The extent to which the structural organization and compartmentalization of the energy-transducing inner mitochondrial membrane to form three components inner boundary membrane, cristal membranes and intercristal space are reflected in, or indeed due to, a different protein complement of each compartment is not fully understood.
The authors concluded that there is restricted diffusion of respiratory complexes through the crista junctions and that the cristae comprise a regulated functionally distinct subcompartment of the inner mitochondrial membrane Gilkerson et al. A similar compartmentalization of cytochrome c oxidase in the cristae has been recorded in Jerusalem artichoke Kay et al.
In addition, indirect evidence to support the hypothesis that the cristal membrane is the site of oxidative phosphorylation comes from examination of Rho 0 cells that lack mitochondrial DNA Gilkerson et al. Human mitochondrial DNA encodes 13 polypeptide components of the respiratory chain and, therefore, in Rho 0 cells, the oxidative phosphorylation machinery is incompletely assembled.
This selective loss of only a small proportion of respiratory complex subunits has a dramatic effect on the internal structure of the mitochondria: the cristal membranes are greatly reduced and disorganized, yet the inner boundary membrane remains visibly unaltered Gilkerson et al. This specific effect on the cristal membranes can be explained if the cristal membranes are functionally distinct from the inner boundary membrane and are dependent on the correct biogenesis of the respiratory chain for their own biogenesis.
Sexual scripts among young heterosexually active men and women: continuity and change
Two supernumerary F 0 -ATPase-associated subunits, g and Tim11p also called ethat are not essential for growth in yeast and are restricted to mitochondria Walker et al. However, although these subunits are conserved between yeast and mammals there are no ificant homologues in Arabidopsis. A similar aberrant mitochondrial phenotype has been described in mutants of a large GTPase called Mgm1p Wong et al. Subsequently, Mgm1p was identified independently by two groups Herlan et al.
Upon import of an Mgm1p precursor, the N-terminal hydrophobic region becomes tethered in the inner membrane at the site of the first transmembrane domain, by what is assumed to be a translocation-arrest mechanism, leaving the N-terminal mitochondrial targeting presequence exposed to the matrix Herlan et al. Cleavage by the matrix-processing peptidase generates what is called the large isoform of Mgm1p l-Mgm1p Herlan et al. Both isoforms function in the maintenance of mitochondrial morphology and respiratory competence, but the mechanism controlling the ratio of l-Mgm1p to s-Mgm1p is unknown Herlan et al.
Recently, Amutha et al. At the time of writing, only DRP3B has been shown to be required for normal mitochondrial morphology Arimura and Tsutsumi,but no information is available on the internal morphology of mitochondria in DRP3B mutants. Contact sites were first described by Hackenbrock as specific regions where the outer membrane and inner boundary membrane are closely apposed, with no discernible space between them.
It is now known that at least two types of contact site exist. One is as described by Hackenbrock, while in the second, the outer and inner boundary membranes are connected by bridge-like structures that maintain a constant separation between the membranes Senda and Yoshinaga-Hirabayashi, ; Perkins et al.
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Senda and Yoshinaga-Hirabayashi suggested that the bridges might keep the outer and inner membranes apart thus maintaining the intermembrane space as a physically distinct compartment. The close apposition of the outer and inner boundary membranes as reported by Hackenbrock led him to suggest that these contact sites could facilitate the passage of solutes and small molecules between the cytosol and the matrix Hackenbrock, Subsequently, it was demonstrated that translationally-arrested polysomes were selectively bound to the outer membrane surface at contact sites Kellems et al.
Using chimeras composed of the N-terminal portion of a mitochondria-targeted precursor protein fused to a cytosolic protein which become trapped during translocation, Pon and colleagues were able to show that the partly translocated precursors are enriched at contact sites and that contact sites contain import activity Pon et al. A similar approach, using arrested translocation intermediates, enabled the co-isolation of the translocase of the outer membrane TOM and the preprotein translocase of the inner membrane TIM23 complex Dekker et al. A component of contact sites in Arabidopsis was identified recently.
The translocase of the inner membrane 17 At TIM was shown to link the inner and outer membranes by means of its C-terminal region that is also essential for protein import Murcha et al.