The language of DNA in form of nitrogen bases read in a set of three termed as codons and it is being translated as language of proteins.
First mRNA is read according to the genetic code which can relate the amino acid sequence to proteins. mRNA can be use as the template to assemble in order the chain of amino acid. Translation starts when the mRNA is decoded and the sequence is elongated until creating an amino acid sequence. Once the stop codon is reached, translation will be stopped and ribosome will release the polypeptide.
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The preceding section reviewed the major metabolic reactions by which the cell obtains and stores energy in the form of ATP. This metabolic energy is then used to accomplish various tasks, including the synthesis of macromolecules and other cell constituents. Thus, energy derived from the breakdown of organic molecules (catabolism) is used to drive the synthesis of other required components of the cell. Most catabolic pathways involve the oxidation of organic molecules coupled to the generation of both energy (ATP) and reducing power (NADH). In contrast, biosynthetic (anabolic) pathways generally involve the use of both ATP and reducing power (usually in the form of NADPH) for the production of new organic compounds. One major biosynthetic pathway, the synthesis of carbohydrates from CO2 and H2O during the dark reactions of photosynthesis, was discussed in the preceding section. Additional pathways leading to the biosynthesis of major cellular constituents (carbohydrates, lipids, proteins, and nucleic acids) are reviewed in the sections that follow.
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Carbohydrates
In addition to being obtained directly from food or generated by photosynthesis, glucose can be synthesized from other organic molecules. In animal cells, glucose synthesis (gluconeogenesis) usually starts with lactate (produced by anaerobic glycolysis), amino acids (derived from the breakdown of proteins), or glycerol (produced by the breakdown of lipids). Plants (but not animals) are also able to synthesize glucose from fatty acids—a process that is particularly important during the germination of seeds, when energy stored as fats must be converted to carbohydrates to support growth of the plant. In both animal and plant cells, simple sugars are polymerized and stored as polysaccharides.
Gluconeogenesis involves the conversion of pyruvate to glucose—essentially the reverse of glycolysis. However, as discussed earlier, the glycolytic conversion of glucose to pyruvate is an energy-yielding pathway, generating two molecules each of ATP and NADH. Although some reactions of glycolysis are readily reversible, others will proceed only in the direction of glucose breakdown, because they are associated with a large decrease in free energy. These energetically favorable reactions of glycolysis are bypassed during gluconeogenesis by other reactions (catalyzed by different enzymes) that are coupled to the expenditure of ATP and NADH in order to drive them in the direction of glucose synthesis. Overall, the generation of glucose from two molecules of pyruvate requires four molecules of ATP, two of GTP, and two of NADH. This process is considerably more costly than the simple reversal of glycolysis (which would require two molecules of ATP and two of NADH), illustrating the additional energy required to drive the pathway in the direction of biosynthesis.
<span>Rhabdomyolysis constitutes a common cause of acute renal failure and presents paramount interest. A large variety of causes with different pathogenetic mechanisms can involve skeletal muscles resulting in rhabdomyolysis with or without acute renal failure. Crush syndrome, one of the most common causes of rhabdomyolysis presents increased clinical interest, particularly in areas often involved by earthquakes, such as Greece and Turkey. Drug abusers are another sensitive group of young patients prone to rhabdomyolysis, which attracts the clinical interest of a variety of medical specialties.
We herein review the evidence extracted from updated literature concerning the data related to pathogenetic mechanisms and pathophysiology as well as the management of this interesting syndrome.
Keywords: Rhabdomyolysis, acute renal failure, myoglobin, crush syndrome
The first case of the crush syndrome, which constitutes one of the main causes of rhabdomyolysis, was reported in Sicily in 1908, after an earthquake1,2. In 1930, in the Baltic area, an epidemic of myoglobinuria was observed due to consumption of contaminated fish. Interest in rhabdomyolysis and crash syndrome was stimulated during the World War II particularly after the bombing in London, where the victims developed acute renal failure and myoglobinuria1.
Rhabdomyolysis is a rupture (lysis) of skeletal muscles due to drugs, toxins, inherited disorders, infections, trauma and compression3. Lysis of muscle cells releases toxic intracellular components in the systemic circulation which leads to electrolyte disturbances, hypovolemia, metabolic acidocis, coagulation defects and acute renal failure due to myoglobin4.
The skeletal muscle consists of cylindrical myofibrils, which contain variant structural and contraction proteins. Actin and myosin, arranged in thin and thick filaments respectively, form the repeated functional units of contraction, the sarcomeres5. The sarcoplasmic reticulum constitutes an important cellular calcium storage. It is structurally connected to the t-tubules, that are formed by invaginations of the muscle cell plasma membrane, the sarcelemma, around every fibril (Figure 1). After the sarcelemma depolarization, the stimulation arrives, through the t-tubules junctions, at the sarcoplasmic reticulum, inducing the calcium ions release and triggering muscle contraction6.</span>
