Cellular protein synthesis

The other major arachidonic acid (AA) converting enzyme is an integral binding protein, 5-lipoxygenase, which is responsible for the initial transformation in a cascade of events towards the biosynthesis of leukotrienes. Leukotrienes are major mediators of numerous biological processes, including chemotaxis, and are implicated in hypersensitivity disorders like asthma. It was discovered in the early 1990s that another protein is necessary for the cellular synthesis of... 

VLDLs are synthesized in the liver and transport triacylglycerols, cholesterol and phospholipids to other tissues, where lipoprotein lipase hydrolyzes the triacylglycerols and releases the fatty acids for uptake. The VLDL remnants are transformed first to IDLs and then to LDLs as all of their apoproteins other than apoB-100 are removed and their cholesterol esterified. The LDLs bind to the LDL receptor protein on the surface of target cells and are internalized by receptor-mediated endocytosis. The cholesterol, which is released from the lipoproteins by the action of lysosomal lipases, is either incorporated into the cell membrane or re-esterified for storage. High levels of intracellular cholesterol decrease the synthesis of the LDL receptor, reducing the rate of uptake of cholesterol, and inhibit HMG CoA reductase, preventing the cellular synthesis of cholesterol. 

The flow of genetic information in normal cells is from DNA to RNA to protein. The synthesis of RNA from a DNA template is called transcription, whereas the synthesis of a protein from an RNA template is termed translation. Cells contain several kinds of RNA messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA), which vary in size from 75 to more than 5000 nucleotides. All cellular RNA is synthesized by RNA polymerase according to instructions given by DNA templates. The activated intermediates are ribonucleoside triphosphates and the direction of... 

Albumin is synthesized primarily by the hepatic parenchymal cells except in early fetal life, when it is synthesized largely by the yolk sac. The synthetic reserve of the liver is enormous in nephrotic syndrome, it may be 300% or more of normal. The synthetic rate is controlled primarily by colloidal osmotic pressure (COP) and secondarily by protein intake. Synthesis is decreased by inflammatory cytokines, and release (but not synthesis) is decreased by hypokalemia. Catabolism occurs primarily by pinocytosis by aU tissue, with lysosomal catabolism of the protein and use of the resulting free amino acids for synthesis of cellular proteins. The rate of pinocytosis is proportional to the local tissue metaboHc rate. Small amounts (10% to 20% of the total catabolized) are also lost into the gastrointestinal tract... 

Temperature and pressure extremes require different strategies. Cellular lipids, proteins and nucleic acids are sensitive to high temperatures. Hyperthermophile bacteria have ether lipids instead of the more hydrolysis sensitive ester lipids in mesophiles [13]. Enzymes from hyperthermophiles show an unusual thermostability in the laboratory, and an important aspect of protein chemistry research is to find out the stabilizing principles. Crude cell extracts of hyperthermophiles show the presence of heat inducible proteins, called chaperones, which assist in the folding of proteins during cellular synthesis. Molecular details for cold adaptation of enzymes have been reported but are less extensively studied [14]. 

In addition to SREBPs, several members of the nuclear receptor superfamily regulate lipid metabolism. Nuclear receptors are transcription factors that are generally activated when bound to specific small-molecule ligands (Chapter 11). Certain nuclear receptors influence whole-body lipid metabolism by regulating the absorption of dietary lipids, cellular synthesis of lipids, transport protein-mediated import and export of lipids, levels of lipoproteins and their receptors, and catabolism of lipids (e.g., fatty acid oxidation in the peroxisome) and their secretion from the body. 

Microorganisms use nutrients in foods for their cellular synthesis and energy. These nutrients include carbohydrates, proteins, lipids, minerals, and vitamins. Foods rich in proteins such as milk and dairy products, meats, and egg are ideal nutrient sources of most foodbome pathogens (McSwane et al 1998). 

Not really. A system rich in amino acids would have at least some peptides. And there are many processes that are easily catalyzed by simple proteins but have never been demonstrated using RNA ribozymes. An example would be the sort of electron transfer mediated by iron sulfur clusters. Cellular synthesis of purines and pyrimidines must be very ancient, but it would seem likely that these are merely representatives of many other processes involving amino acids and peptides. 

DNRA is a process that reduces nitrate to ammonia (Figure 8.43). This process is carried out by dissimilative nitrate reductase enzymes. Dissimilative nitrate reductases are membrane-bound proteins, whose synthesis is repressed by molecular oxygen and thus are only synthesized under anoxic conditions. For this reason, DNRA is mediated by obligate anaerobes that use nitrate as alternate electron acceptor in the process of cellular respiration. 

The cellular synthesis of HA is a unique and highly controlled process. HA is naturally synthesized by a class of integral membrane proteins called hyaluronan synthases, of which vertebrates have three types HASl, HAS2, and HAS3 [19,20], See-ondaiy structure predictions and homology modeling indicate an integral membrane... 

Cellular aspects of protein polysaccharide synthesis, including intracellular sites of synthesis, mechanism of secretion, and regulation of polysaccharide biosynthesis in the intact cell. 

Most reactions in cells are carried out by enzymes [1], In many instances the rates of enzyme-catalysed reactions are enhanced by a factor of a million. A significantly large fraction of all known enzymes are proteins which are made from twenty naturally occurring amino acids. The amino acids are linked by peptide bonds to fonn polypeptide chains. The primary sequence of a protein specifies the linear order in which the amino acids are linked. To carry out the catalytic activity the linear sequence has to fold to a well defined tliree-dimensional (3D) stmcture. In cells only a relatively small fraction of proteins require assistance from chaperones (helper proteins) [2]. Even in the complicated cellular environment most proteins fold spontaneously upon synthesis. The detennination of the 3D folded stmcture from the one-dimensional primary sequence is the most popular protein folding problem. 

Many human diseases are caused when certain proteins are either over- or underexpressed. Eor example, breast cancer can be induced by overexpressing certain cellular oncogenes within mammary tissue. To study the disease, researchers produce a line of transgenic mice that synthesize an abnormal amount of the same protein. This leads to symptoms of the disease in mice that are similar to what is found in humans. A protein can be overexpressed by inserting a DNA constmct with a strong promotor. Conversely, underexpression of a protein can be achieved by inserting a DNA constmct that makes antisense RNA. This latter blocks protein synthesis because the antisense RNA binds and inactivates the sense mRNA that codes for the protein. Once a line of mice is developed, treatments are studied in mice before these therapies are appHed to humans. 

Estrogens stimulate cellular proliferation, induce RNA and protein synthesis of uterine endometrium and the fibrous connective tissue framework for ovaries, and increase the size of the cells. This effect leads to the growth and regeneration of the endometrial layer and spinal arterioles, and increase in the number and size of endometrial glands. Under the influence of estrogen, vaginal mucosa becomes thicker, as cervical mucus becomes thinner (85,86). 

Cellular protein biosynthesis involves the following steps. One strand of double-stranded DNA serves as a template strand for the synthesis of a complementary single-stranded messenger ribonucleic acid (mRNA) in a process called transcription. This mRNA in turn serves as a template to direct the synthesis of the protein in a process called translation. The codons of the mRNA are read sequentially by transfer RNA (tRNA) molecules, which bind specifically to the mRNA via triplets of nucleotides that are complementary to the particular codon, called an anticodon. Protein synthesis occurs on a ribosome, a complex consisting of more than 50 different proteins and several stmctural RNA molecules, which moves along the mRNA and mediates the binding of the tRNA molecules and the formation of the nascent peptide chain. The tRNA molecule carries an activated form of the specific amino acid to the ribosome where it is added to the end of the growing peptide chain. There is at least one tRNA for each amino acid. 

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