Ultra structure of mitochondria

Mitochondria are double-membrane enclosed eukaryotic organelles with a central role in numerous cellular functions. The ultrastructure of mitochondria varies considerably between tissues, organisms, and the physiological state of cells. Alterations and remodeling of inner membrane structures are evident in numerous human disorders and during apoptosis. The inner membrane is composed of two subcompartments, the cristae membrane and the inner boundary membrane. Recent advances in electron tomography led to the current view that these membrane domains are connected by rather small tubular structures, termed crista junctions. They have been proposed to regulate the dynamic distribution of proteins and lipids as well as of soluble metabolites between individual mitochondrial subcompartments. One example is the release of cytochrome c upon induction of apoptosis. However, only little is known on the molecular mechanisms mediating the formation and maintenance of cristae and crista junctions. Here we review the current knowledge of the factors that determine cristae morphology and how the latter is linked to mitochondrial function. Further, we formulate several theoretical models which could account for the de novo formation of cristae as well as their propagation from existing cristae. • Previous article in issue • Next article in issue

Muscle-Skeletal Muscle-Gross and Ultra Structure Muscle • The word muscle is derived from Latin word “musculus” which means little mouse. It is named so because of the movement of muscle under the skin resembles a running mouse. Joints make a skeleton potentially movable and bones provides a basic system of levers but bones and joints cannot move by themselves. The driving force behind the movement is the muscle. There are three types of muscles • Smooth muscle • Cardiac muscle • Skeletal muscle 1. Skeletal muscle • Skeletal muscle is attached to bone and helps in movement. It is also known as striated muscle because the muscle fibers shows alternate dark and light band under light microscope. Muscle are usually in a partial contracted state which give muscle tone and make ready for contraction under the stimulus preceding a complete contraction. Gross structure: • Muscle is composed of muscle cell, which are called as muscle fibres because they are so long, cylindrical shape multi nucleated cell more resemble to fibre than cell. They are arranged parallel to each other. • Each fibre is multimucleated and the nucleus are located near the surface of each fibre. • Bundle of fibres are surrounded by collagen fibres and connective tissues. • Each muscle fibres is enclosed by a plasmamembrane called Sarcolemma. • The cytoplasm is known as sarcoplasm which contain large number of mitochondria. Ultra structure: • Muscle fibre is composed of large number of myofibril arranged para...

We report a three dimensional (3D) quantitative visualization of a mammalian mitochondrion by coherent x-ray diffractive imaging (CXDI) using synchrotron radiation. The internal structures of a mitochondrion from a mouse embryonic fibroblast cell line (NIH3T3) were visualized by tomographic imaging at approximately 60 nm resolution without the need for sectioning or staining. The overall structure consisted of a high electron density region, composed of the outer and inner membranes and the cristae cluster, which enclosed the lower density mitochondrial matrix. The average mass density of the mitochondrion was about 1.36 g/cm 3. Sectioned images of the cristae reveal that they have neither a baffle nor septa shape but were instead irregular. In addition, a high resolution, about 14 nm, 2D projection image was captured of a similar mitochondrion with the aid of strongly scattering Au reference objects. Obtaining 3D images at this improved resolution will allow CXDI to be an effective and nondestructive method for investigating the innate structure of mitochondria and other important life supporting organelles. Over the last few decades, there has been enormous effort to visualize the internal structures of cellular organelles utilizing a variety of microscopy techniques such as optical, fluorescence, and electron microscopies Coherent x-ray diffractive imaging (CXDI), which has the ability to visualize non crystalline specimens nondestructively at about 10~20 nm resolution,...

Giant mitochondria are peculiarly shaped, extremely large mitochondria in hepatic parenchymal cells, the internal structure of which is characterised by atypically arranged cristae, enlarged matrix granules and crystalline inclusions. The presence of giant mitochondria in human tissue biopsies is often linked with cellular adversity, caused by toxins such as alcohol, xenobiotics, anti-cancer drugs, free-radicals, nutritional deficiencies or as a consequence of high fat Western diets. To date, non-alcoholic fatty liver disease is the most prevalent liver disease in lipid dysmetabolism, in which mitochondrial dysfunction plays a crucial role. It is not well understood whether the morphologic characteristics of giant mitochondria are an adaption or caused by such dysfunction. In the present study, we employ a complementary multimodal imaging approach involving array tomography and transmission electron tomography in order to comparatively analyse the structure and morphometric parameters of thousands of normal- and giant mitochondria in four patients diagnosed with non-alcoholic fatty liver disease. In so doing, we reveal functional alterations associated with mitochondrial gigantism and propose a mechanism for their formation based on our ultrastructural findings. Mitochondria are unique double-membrane bounded organelles that primarily function in cellular respiration via the oxidative phosphorylation of carbohydrates and fatty acids to produce adenosine triphosphate (ATP) ...