Amino acid common

This table lists the and pi (pH at the isoelectric point) values of a-amino acids commonly found in proteins along with their abbreviations. The dissociation constants refer to aqueous solutions at 25°C. 

Histidine is one of the 20 naturally occurring amino acids commonly found in proteins (see Chapter 4). It possesses as part of its structure an imidazole group, a five-membered heterocyclic ring possessing two nitrogen atoms. The pAl for dissociation of the imidazole hydrogen of histidine is 6.04. 

The structures and abbreviations for the 20 amino acids commonly found in proteins are shown in Figure 4.3. All the amino acids except proline have both free a-amino and free a-carboxyl groups (Figure 4.1). There are several ways to classify the common amino acids. The most useful of these classifications is based on the polarity of the side chains. Thus, the structures shown in Figure 4.3 are grouped into the following categories (I) nonpolar or hydrophobic... 

FIGURE 4.1 Anatomy of an amino acid. Except for proline and its derivatives, all of the amino acids commonly found in proteins possess this type of structure. 

The structures, abbreviations (both three- and one-letter), and pKa values of the 20 amino acids commonly found in proteins are shown in Table 26.1. All are... 

In addition to the twenty amino acids commonly found in proteins, two others—selenocysteine and pyrrolysine—are found in some organisms, and more than 700 nonprotein amino acids are also found in nature. y-Amino-butyric acid (GABA), for instance, is found in the brain and acts as a neurotransmitter homocysteine is found in blood and is linked to coronary heart disease and thyroxine is found in the thyroid gland, where it acts as a hormone. 

Figure 2.1 The chemical structure of the 20 amino acids commonly found in proteins...

Of the 20 amino acids commonly found in proteins, eight are classified as hydrophobic, due to the non-polar nature of their side chains (R groups, Figure 6.12). Most proteins are folded such... 

Other than the sweeteners discussed so far thaumatin is a polypeptide consisting of amino acids commonly found in food proteins. It is quickly and completely digested like proteins and did, after demonstration of its metabolic characteristics, only require a rather limited set of safety data. In contrast to the other intense sweeteners the ADI of thaumatin is not specified , as for substances of similar composition.27 It is approved in many countries but, owing to its flavour enhancing properties, is often used as a flavour enhancer rather than a sweetener. 

Fig. 3. Comparison of the amino acid sequences predicted from the a- and j3-tubulin mRNA sequences. Open circles indicate homologous, conservative substitutions, and boxed regions indicate areas of high homology. For completeness, the sequence of the first 25 amino acids of chick brain a-tubulin, deduced by the work of Luduena and Woodward (1973), is also included. Note that the asterisks indicate identical amino acids common to both polypeptide chain sequences. [Reproduced from Valenzuela et al. (1981). Nature (London) 289, 650-655.]...

The pyrrolidine ring, with its secondary amine also confers unusual chemical and biological properties, compared with the primary amino acids commonly found in proteins (Figure 7). " ... 

Glutamic add an amino acid commonly found in proteins and the most important excitatory neurotransmitter in the human central nervous system. 

Dreizen S, Spirakis CN and Stone RE (1964) In vitro studies of the chromogenic reactions between selected carbohydrate derivatives and the amino acids common... 

Note 3 Propagation in chain polymerization usually occurs without the formation of small molecules. However, cases exist where a low molar-mass by-product is formed, as in the polymerization of oxazolidine-2,5-diones derived from amino acids (commonly termed amino acid A-carboxy anhydrides). When a low-molar-mass by-product is formed, the adjective condensative is recommended to give the term condensative chain polymerization. 

The primary metabolites Include such compounds as simple sugars, amino acids, common lipids, the common nitrogen compounds and many phosphorylated compounds. 

The 20 amino acids commonly found as residues in proteins contain an a-carboxyl group, an a-amino group, and a distinctive R group substituted on the a-carbon atom. The a-carbon atom of all amino acids except glycine is asymmetric, and thus amino acids can exist in at least two stereoisomeric forms. Only the... 

Transfer RNAs (tRNAs), the smallest of the three major species of RNA molecules (4S), have between 74 and 95 nucleotide residues. There is at least one specific type of tRNA molecule for each of the twenty amino acids commonly found in proteins. Together, tRNAs make up about fifteen percent of the total RNA in the cell. The tRNA molecules contain unusual bases (for example, pseudouracil, see Figure 22.2, p. 290) and have extensive intrachain base-pairing (Figure 30.3). Each tRNA serves as an "adaptor molecule that carries its specific amino acid—covalently attached to its 3-end—to the site of protein synthesis. There it recognizes the genetic code word on an mRNA, which specifies the addition of its amino acid to the growing peptide chain (see p. 429). 

At least one specific type of tRNA is required per amino acid. In humans, there are at least fifty species of tRNA, whereas bacteria contain thirty to forty species. Because there are only twenty different amino acids commonly carried by tRNAs, some amino acids have more than one specific tRNA molecule. This is particularly true of those amino acids that are coded for by several codons. 

Values of pK for the Ionizable Groups of the Twenty Amino Acids Commonly Found in Proteins... 

Nineteen of the 20 amino acids commonly found in proteins have a carboxyl group and an amino group attached to an a-carbon atom they differ in the side chain attached to the same a carbon. 

Escherichia coli has served as the organism of choice for examining the pathways for amino acid biosynthesis for two reasons (1) E. coli synthesizes all 20 amino acids commonly found in proteins, and (2) E. coli is an organism ideally suited for genetic and biochemical studies. 

Proteins are informational macromolecules, the ultimate heirs of the genetic information encoded in the sequence of nucleotide bases within the chromosomes. Each protein is composed of one or more polypeptide chains, and each peptide chain is a linear polymer of amino acids. The order of the amino acids commonly found in the polypeptide chain is determined by the order of nucleotides in the corresponding messenger RNA template. In this chapter we examine four aspects of protein metabolism (fig. 29.1) (1) The process whereby amino acids are ordered and polymerized into polypeptide chains (2) posttranslational alterations in polypeptides, which occur after they are assembled on the ribosome (3) the targeting process whereby proteins move from their site of synthesis to their sites of function and (4) the proteolytic reactions that result in the return of proteins to their starting material, amino acids. 

In a recent paper, 17 amino acids commonly present in Sauvignon wine from the Coastal region of Croatia were determined by complete assignment of their resonances by the use of aH and 13C NMR spectroscopy (Kosir and Kidric, 2001). In 2003, the metabolite content of the skin and pulp of mature berry extracts for four wines from the Bordeaux area were analyzed (Pereira et ah, 2005). Differences readily observed were due to an absence of polyphenol content in pulp extracts (Fig. 4.20). PCA highlighted that sugars were mainly responsible for cluster separation among samples in both types of extracts. 

Twenty standard amino acids commonly occur in nature. They differ in the structure of the side chain that is attached to the a-carbon (the R group in the previous structure). Table 26.1 shows the structures of the standard amino acids at pFI 7, along with their names and abbreviations. 

S. W. Fox and K. Harada (1960). Thermal copolymerization of amino acids common to proteins. 

When proteins are hydrolyzed with acid at high temperature, they are broken down to their constituent amino acids. Commonly, the amino acid cystine is found among them. But cystine is not included among the amino acids listed in the dictionary of codons. Why ... 

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