By X. Campa. Texas State University.
They are involved in generating energy for cells by breaking down of saccharides purchase 75 mg venlor free shipping, lipids and other energy-rich organic compounds venlor 75 mg visa. Their number is in a direct proportion to the intensity of cell’s energy metabolism. The outer membrane encloses it while the inner one is folded into the mitochondrial cristae expanding its surface. The space between the cristae is filled with mitochondrial matrix made up of phospholipoproteins and ions of calcium and magnesium. They are synthesized on endoplasmic reticulum, modified in the endoplasmic reticulum and completed in Golgi apparatus. Consequently, they are transported into mitochondria where they are enhanced with proteins synthesized in mitochondria and become functional. They contain chlorophyll and are involved in photosynthesis (the transformation of the light energy into the energy of chemical bonds in the glucoses). Similarly as mitochondria, they contain their own genetic information and ribosomes – of prokaryotic type. From the morphological and functional aspect, we distinguish between two types of endoplasmic reticulum. The muscle cells contain a special form of endoplasmic reticulum – the 2+ sarcoplasmic reticulum. It ensures the transport of Ca cations that are inevitable for muscle contraction. For further processing they are transported in a vesicle from the membrane into the Golgi apparatus. Proteins synthesized on the endoplasmic reticulum, usually enclosed in a transport vesicle, come to the cis side. They leave Golgi apparatus from the trans side in the form of vesicles to cytoplasm. Some of them fulfill specific tasks in a cell, others join the cytoplasmic membrane and their content comes into the extracellular environment. Following connection with an unneeded organelle or pinocytotic (fagocytotic) vesicle creates a secondary lysosome and lysosomal enzymes break down the content of these structures. In plant cells and some protists, the function of lysosomes and many other tasks is performed by vacuoles. Peroxisomes belong to the large family of vesicles in cytoplasm, the role of which is to ensure activity of various enzymes. Enzymes in the cytosolic vesicles are thus available for the cell; however, they are not directly contained in the cytoplasm, but used when the cell needs them. It participates in forming of the shape of cells, distribution of organelles and performing of some intracellular activities (e. Cytoskeleton consists of protein-based microtubules, microfilaments, intermediate filaments and microtrabecules, while each of these plays a different role. They are long, firm and hollow cylinders about 25 nm in diameter comprising the molecules of tubulin (dimers consist of α and β monomers). Microtubules are made longer or shorter through polymerization and de- polymerization (adding or removing of tubulin dimers). They participate in the transport of vesicles between endoplasmic reticulum, the Golgi apparatus and cytoplasmic membrane. They play an important role as part of mitotic spindle fibers in the movement of chromosomes during cell division. Microfilaments are thin (7 nm in diameter) filaments of helical structure made up of globular protein called actin to which the proteins of myosin are bound together creating (via clutching) a contractile system of muscle cells. Intermediate filaments are think fibers (10 nm in diameter) that are not able of contraction. They also participate in the distribution of organelles and inclusion within a cell. Kinetochore, a structure important for cell division, is also made up of proteins. It is the protein complex attaching to the centromere of chromosomes (chromatids) and enabling in the course of cell division free attachment of tubulin fibers of the mitotic spindle. It consists of two complexes of three couples of orthogonally arranged tubulin fibers (centrioles). They are made up of a large and small sub-unit that is connected only during translation (the protein synthesis). Prokaryotic ribosomes are smaller, but their gravitation density if 70S (Svendberg units, determining the sedimentation speed at ultracentrifugation). The ribosomes of eukaryotic cells are larger and their gravitation density is 80S. This enables the eukaryotic cell to effectively manage the course of protein synthesis. In the eukaryotic cells there are also ribosomes of the prokaryotic type, specifically in mitochondria and chloroplasts.
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