Cell amino acids

In living cells, amino acids are linked into polymeric chains known as polypeptides, typically containing between 10 and 100 amino acids [the... 

Figure 8.5 Act/Ve amino add transport into cells. Amino acids are transported into cells against their concentration gradient coupled to Na ion transport down its concentration gradient. The Na ion is transported out in exchange for K -ions, via the NayK ATPase, Chapter 5).

Regardless of the exact mechanism of infection, the virus essentially commands the cell to synthesize the enzymes that produce more copies of viral DNA or RNA and to synthesize structural proteins that will ultimately be used to form new viral shells or capsids. Thus, the virus uses the biosynthetic machinery as well as the structural components and nutrients of the cell (amino acids, nucleic acids, etc.) to replicate itself. Likewise, the virus often incapacitates the infected cell so that the infected cell cannot carry out its normal physiologic activities. 

Amino acid metaboli.sm following dietary protein intake. Digestion of protein produces amino acids. Within the intestinal cell, amino acid interconversions form alanine, which is delivered by the portal blood to liver, where it serves as the source of cr-amino nitrogen and pyruvate, which is converted to lipid and glucose. Excess nitrogen is converted to urea. Branched-chain amino acids (BCAAs) are not taken up by the liver but enter peripheral tissues such as muscle where they serve as an important fuel source. Their a-amino nitrogen is transported to liver in the form of alanine. 

Specific transport systems are most likely present in the plasmalemma of the mammalian cell to efficiently channel circulating amino acids into the cell interior. Inside the cell, amino acids are involved in a variety of metabolic processes. A substantial part of the amino acids is used for the protein synthesis that takes place in all mammalian cells with the exception of red blood cells. It is important to realize that protein synthesis only occurs when all amino acid precursors, that is, both essential and nonessential amino acids, are present in adequate amounts. When one... 

Fig. 1. Summary of amino acid metabolism. Dietary proteins are digested to amino acids in the stomach and intestine, which are absorbed by the intestinal epithelium, transferred to the circulation, and taken up by cells. Amino acids are used to synthesize proteins and other nitrogen-containing compounds. The carbon skeletons of amino acids are also oxidized for energy, and the nitrogen is converted to urea and other nitrogenous excretory products.

An individual has been shown to have a deficiency in an intestinal epithelial cell amino acid transport system for leucine. However,... 

In present-day cells, amino acids (the monomers) combine by polymerization to form proteins, nucleotides (also monomers) combine to form nucleic acids, and the polymerization of sugar monomers produces polysaccharides. Polymerization experiments with amino acids carried out under early-Earth conditions have produced proteinlike polymers. Similar experiments have been done on the abiotic polymerization of nucleotides and sugars, which tends to happen less readily than the polymerization of amino acids. Proteins and nucleic acids play a key role in life processes. 

The surfaces of some gram-negative bacteria have structures called fimbriae, also known as pill. Many of these structures have been identified as attachment vehicles. Pili are, for the most part, composed of protein, so they tend to react with specific proteinaceous sites based on host cells—amino acids, sequencing, and peptide configurations. 

Figure 19 Representative set of noncanonical amino acids that have been incorporated into proteins in cells. Amino acids shown in black are incorporated by cells that are auxotrophic for the canonical amino acid, but are otherwise wild type . Amino acids shown in blue require overexpression of the wild-type aminoacyl-tRNA synthetase. Amino acids shown in green require expression of an editing-impaired aminoacyl-tRNA synthetase. Analogs drawn in red require expression of a synthetase with an engineered substrate-binding pocket.

Isoleucine is > 5% of the cell amino acids. Serine is > 5% of the cell amino acids. Threonine is > 5% of the cell amino acids. Cysteine is > 5% of the cell amino acids. Cystine is > 5% of the cell amino acids. 

Active ammo acid T. has certain similarities with the active T. of glucose, especially from the intestine into the blood. More than five difrerent T. systems are known. In some cells amino acid T. also appears to be coupled with a Na gradient. 

In the living cell, amino acid activation and binding to tRNA probably occurs in a single step, catalyzed by a single macromolecular complex. But, for the sake of clarity, amino acid activation is described as a separate event. 

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