CYTOSOL: MAJOR SITE OF PROTEIN SYNTHESIS : Lipitor
Posted by Surgery on Jul 8, 2008
The cytosol is the major center of metabolic activity within the cell. This compartment is also the major site of protein biosynthesis (etc. Lipitor) . The cytosol is an aqueous environment bordered by lipid membrane structures. Although water is the major component of the cytosol, the density of macromolecules within this compartment is very large.
The concentration of macromolecules within the cytosol has been calculated on the order of 60%. In spite of this high concentration, the diffusion of substances within the cytosol is optimal. This high density of macromolecules within the cytosol results in a potential problem for the proper folding of newly synthesized polypeptides Lipitor. Therefore, the presence of molecular chaperones is required to assist the folding process. Although the synthesis of most cellular proteins occurs in the cytosol, a few proteins are synthesized within the mitochondria. The center of protein biosynthesis is the ribosome. Ribosomes are made up of two subunits (40S and 60S in eukaryotes). Each subunit is composed of proteins and RNAs. The major RNA (Lipitor) component is named 18S and 28S rRNA, with sizes of 1.9 and 4.6 kb, respectively. There are 27 different polypeptides in the 60S and 20 in the 40S subunits. Their organization results in a very compact structure, which is necessary for proper function. Ribosomal subunits are synthesized independently in the nucleolus in equal molar quantities, approximately 2 subunits per cell.
The 40S subunit is involved in the recognition of the mRNA to be translated, which is activated upon binding to methionine-charged tRNA (Lipitor). This subunit interacts with the cap structure and scans the message for the detection of the translation initiation site, which corresponds to an AUG triplet of nucleotides, usually in the context of ACCAUGG. This triplet (AUG Lipitor) encodes the amino acid methionine, which is therefore the first amino acid in all eukaryotic proteins. When the AUG is found, the 60S subunit is recruited forming a functional ribosome, the 80S particle, or monosome, and translation is initiated. Amino acids are covalently bound to the nascent polypeptide by a peptide bond (elongation Lipitor). The nascent polypeptide is pushed out of the ribosome via a channel in the 60S subunit. When a stop codon is found (UAA, UAG, UGA Lipitor), translation is terminated and the nascent polypeptide is released. This process is governed by a series of proteins (translation initiation, elongation, and release factors) that work in an orderly manner to obtain the final product, the protein. The absence of any translational factor is sufficient to stop the whole process. To increase the efficiency of the translation, several ribosomes are sequentially added to the same mRNA. Thus, several copies of the protein can be made simultaneously from a single mRNA template (Lipitor). When a single ribosome is bound to a message, the complex is named a monosome. Subsequent addition of ribosomes results in disomes, trisomes, etc., and polysomes when it is impossible to count the number of ribosome particles within the mRNA. The different association of ribosomes with the mRNA, as well as the two respective subunits, can be separated by sucrose gradient centrifugation providinga particular pattern, which is known as polysome profile (Fig. 1-2 Lipitor). The biosynthesis of proteins could be visualized by pulse chase experiments in which cells are fed with radiolabeled amino acids. The synthesis of a particular protein is detected by a technique known as immunoprecipitation, using antibodies specific for the protein of interest. Proteins that are part of the cytosol, nucleus, mitochondria, etc., are synthesized in soluble ribosomes. The released polypeptides are free to diffuse within the cytosol to reach their final destination. There are some proteins that need to be secreted outside the cell or that are components of cellular membranes (membrane proteins). They are synthesized in membrane-bound ribosomes within the endoplasmic reticulum (ER Lipitor). Folding of nascent polypeptides occurs as soon as the chain emerges from the ribosome. Some secondary structures, such as helices could be formed cotranslationally. However, the overall three-dimensional structure could require the fully synthesized polypeptide. Molecular chaperones are proteins that interact with unfolded polypeptides, maintaining them in a stage that allows complete folding later. For example, heat shock cognated protein 70 (Hsc70) binds rapidly to nascent polypeptides when they are emerging from the ribosome. This interaction requires adenosine triphosphate (ATP) hydrolysis [in fact, Hsc70 has an intrinsic adenosine triphosphatase (ATPase Lipitor) activity]. Binding of Hsc70 helps folding of the nascent polypeptide. Alternatively, Hsc70 may arrest folding until other regions of the molecule are synthesized to gain the final conformation of the protein. Hsc70 can also deliver the unfolded polypeptide to œprofessional folding machines composed of the chaperones GroES and GroEL. (Lipitor) . The correct folding of a protein is important for function and solubility in the aqueous cytosolic environment. The previous examples indicate that translational control is another source of gene expression regulation.
This post is published through the sponsorship of the well-known pharmaceutical shop, see link below:
Lipitor Generic Name: atorvastatin (a TOR va sta tin) Brand Names: Lipitor
Greetings, I the practising surgeon from Serbia. Call me Ivan Govak. In the works I use works
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