Alpha Amino Acids
Alpha amino acids are organic compounds that serve as the building blocks of proteins. They contain both an amino group and a carboxylic acid group, with the amino group attached to the carbon atom adjacent to the carboxyl group. This arrangement gives them the "alpha" designation. There are 20 standard alpha amino acids commonly found in proteins, each with a unique side chain.
8 Key excerpts on "Alpha Amino Acids"
eBook - ePubBiochemistry
An Organic Chemistry Approach
- Michael B. Smith(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...11 Amino Acids There is an important class of difunctional molecule that is critical to an understanding of biological processes. Amino acids comprise the backbone of peptides, and thereby of enzymes. This chapter will discuss the structure, nomenclature, and characteristics of amino acids. 11.1 Characteristics of Amino Acids An amino acid, as the name implies, has one amine unit (–NR 2) and one carboxylic acid unit (a carboxyl group, COOH). The nomenclature for a generic amino acid is dominated by the carboxyl, so the parent name is “acid” and the NR 2 unit is treated as a substituent. When an amine unit is a substituent the name “amino” is used, so these compounds are amino carboxylic acids, or just amino acids. Amino acids are easily named using IUPAC nomenclature and the carboxylic acid is the parent for each new compound. Two examples are 2-aminopropanoic acid (known as alanine) and 5-amino-3,5-dimethylheptanoic acid. There are a variety of structural variations for amino acids. If the amine unit is attached to C2, the α-carbon of the carboxylic acid chain, the compound is an α-amino acid. If the amine group is on C3, the β-carbon it is a β-amino acid. Similarly, there are γ-amino acids, δ-amino acids, and so on. Due to their biological importance, α-amino acids will be discussed most of the time. The common names of α-amino acids are presented in Table 11.1 in Section 11.2. To distinguish α-amino acids from other amino acids, the term non-α-amino acids is used. 5-Amino-3,5-dimethylheptanoic acid is a non-α-amino acid, for example. Table 11.1 Structures, Names, Three-Letter Code and One-Letter Code of the 20 Essential Amino Acids, Based on the Structure in Figure 11.5 R Name Three-Letter Code One-Letter...
eBook - ePub- Guoyao Wu(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
...The other carbon atoms of the AA beyond the α -carbon are named in sequence according to the Greek alphabet, that is, ß-, γ -, δ -, or ε -carbon. If the amino group (− NH 2) is linked to the α -carbon, the AA is called an α -AA. Likewise, if the amino group is linked to the ß-, γ -, δ -, or ε -carbon, the AA is known as a ß-, γ -, δ -, or ε -AA, respectively. All of these types of AAs occur in nature. Imino Acids Proline and hydroxyproline are special nitrogenous compounds with a pyrrolidine ring. They contain a secondary α -amino (α -imino; − NH) group and therefore are α -imino acids (Phang et al. 2008). The chemical reactivity of the imino group differs remarkably from that of the amino group. Since proline is a common substrate for protein synthesis like α -AAs and hydroxyproline is the posttranslational derivative of proline, both proline and hydroxyproline are loosely referred to as α -AAs in biochemistry and nutrition. Hydroxyproline occurs as both 4-hydroxyproline (the major form) and 3-hydroxyproline (the minor form) in animals, but is rare in plants and microbes. Differences in the Structures of AAs The numbers of amino and acid groups, as well as side-chain groups, vary with AAs (Greenstein and Winitz 1961). For example, glutamate and aspartate have two carboxyl groups and one α -amino group, whereas lysine and ornithine have two amino groups and one carboxyl group. Both arginine and some of its metabolites (e.g., methylarginines and homoarginine) possess a guanidino group, while other members of the arginine family of AAs, citrulline and homocitrulline, contain a ureido group. Although most AAs have a straight carbon chain (e.g., alanine, glutamine, and glycine), some AAs (e.g., leucine, isoleucine, and valine) are branched in structure. The differences in the side chains of AAs greatly affect their chemical properties. All AAs are composed of nitrogen (N), carbon (C), oxygen (O), and hydrogen (H) atoms...
eBook - ePub- Raymond S. Ochs(Author)
- 2021(Publication Date)
- CRC Press(Publisher)
...5 Amino Acids and Proteins The word protein is of Greek origin, meaning “first place” or primary. Berzelius originated this term in 1838 to identify a substance found in plant fibers essential for animal nutrition. This identification was well before the molecular nature of proteins was discovered. Proteins are the most diverse of biomolecules. They include structural proteins (such as the plant fibers), binding proteins (such as hemoglobin), and enzymes (such as sucrase). In this chapter, we examine protein structure and some elements of their binding behavior. In the next, we examine their function as enzymes. The proteins also play a central role in all subsequent chapters of the book, commensurate with their paramount importance in biochemistry. 5.1 Common Structure of the Amino Acids All amino acids contain an amine group (most commonly a primary amine) and a carboxyl group (the acid portion) attached to the same carbon. The latter is called the α-carbon, from an organic chemistry nomenclature system that assigns Greek letters to carbons adjacent to carboxyl groups: α, β, etc (Figure 5.1). Note that this is a distinctive use of the Greek lettering system from the carbohydrates. Also bound to the α-carbon is a hydrogen atom (the α-hydrogen) and a variable group designated as R (Figure 5.2). Twenty different R groups make up the common amino acids, meaning those incorporated into proteins. Except for glycine (for which R is a hydrogen atom), the α-carbon is chiral and designated as l or d by comparison to the reference molecule glyceraldehyde, illustrated in Figure 5.3 for the case of alanine (in which R is –CH 3). The carboxyl group of alanine is most similar to the carbonyl group of glyceraldehyde. The amine group of alanine is most similar to the OH group of glyceraldehyde. In nature, virtually all amino acids are present in the l form. FIGURE 5.1 Organic carboxyl bearing chain numbering...
eBook - ePubBiochemistry Explained
A Practical Guide to Learning Biochemistry
- Thomas Millar(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
...4 Amino Acids and their Functions In this chapter you will learn: the functional groups: an amine and carboxyl groups to understand the general structure of amino acid the structures, names and single letter symbols for the 20 amino acids found in proteins how 2 cysteines may be oxidised to form the bridging amino acid cystine how the carbons of amino acids are named or numbered the terms ampholyte and zwitterion and how these relate to amino acids the structure of an amide bond and the special case a peptide bond special functions of amino acids (e.g. neurotransmitters) and structural relationships between amino acids how ketones are formed from amino acids by removing ammonia from the αC the synthesis of the bioactive amines dopamine, noradrenaline, adrenaline and serotonin. to understand the basis for Parkinson’s disease and phenylketonuria that tyrosine, serine and threonine are phosphorylation sites in proteins the importance of decarboxylation in the formation of some active amines such as histamine how sugars may attach to the amino acids serine, threonine and asparagine Basic structure and nomencalture of amino acids The name amino acid suggests that these structures have an amine and an acid group. Indeed this is true; amino acids have an amino group and a carboxylic acid. The structure of a typical L-amino acid is illustrated below. This type of amino acid is the basis of proteins. Q&A 1 : Draw the chemical structures of a carboxylic acid, and an amine group. There is a central carbon that has bonds to an amine group, a carboxylic acid, an hydrogen and a variable R group. Since this central carbon has 4 different groups attached to it, it is a chiral carbon and hence there are 2 possible isomers, L and D. Nearly all amino acids in biochemistry are of the L-form (L for life). Note that this is the opposite of sugars, which nearly always occur as the D isomer. You need to learn their structure in this orientation...
eBook - ePub- S. P. Bhutani(Author)
- 2019(Publication Date)
- CRC Press(Publisher)
...That means they have the same relative configuration as L -glyceraldehyde. As the two functional groups present in amino acids are acidic and basic, all amino acids are amphoteric and actually exist as zwitterions. Thus, the simplest amino acid glycine exists in the form shown below rather than aminoacetic acid. H 2 N—CH 2 — COOH ⇄ H 3 N + — CH 2 — CO O ¯ Aminoacetic acid Zwitterion 2.3 CLASSIFICATION OF AMINO ACIDS The 22 α-amino acids that are obtained from proteins can be classified into four different groups on the basis of the structures of their side chains: 1. Neutral Amino Acids 2. Acidic Amino Acids 3. Neutral Amino Acids with Polar Side Chains 4. Basic Amino Acids These are listed with their symbols, abbreviations and structures in Table 2.1. Only 20 of the 22 amino acids listed in Table 2.1 are actually used by cells when they synthesise proteins. Hydroxyproline is synthesised from proline and cystine is synthesised from cysteine. Asparagine and glutamine are derived from aspartic acid and glutamic acid. TABLE 2.1 Amino Acids Commonly Found in Proteins 2.4 THE ESSENTIAL AMINO ACIDS Amino acids are synthesised by all living organisms, animals and plants for their protein requirements. The biosynthesis of proteins requires the presence of all the constitutent amino acids. If one of the 20 amino acids is missing or in short supply, protein biosynthesis is inhibited. Some organisms, such as E.Coli can synthesise all the amino acids that they need. However, the human body is unable to synthesise some of these amino acids required for making proteins. These are called essential amino acids. For adult humans there are ten amino acids, which have been designated with the superscript e in Table 2.1. They must be included in our diet. We eat proteins, break them down in our body to their constituent amino acids and then use some of these amino acids to build up other proteins which we require to maintain good health...
eBook - ePub- Raja Sivamani, Jared R. Jagdeo, Peter Elsner, Howard I. Maibach, Raja Sivamani, Jared R. Jagdeo, Peter Elsner, Howard I. Maibach(Authors)
- 2015(Publication Date)
- CRC Press(Publisher)
...Chapter 15 Amino Acids and Derivatives Kazutami Sakamoto Introduction Amino acids are molecules with both an amino group and carboxylic group. There are 20 kinds of naturally occurring amino acids with optical active structures at α-position (L-amino acids) except glycine. Greenstein and Winitz said: “Few products of natural origin are versatile in their behavior and properties as are the amino acids, and few have such a variety of biological duties to perform” in their preface of Chemistry of the Amino Acid in 1961. 1 Subsequently significant progress has been made on the knowledge of amino acids, and technical achievements to utilize such progress are remarkable, including cosmetic and cosmeceutical applications. This is due to the market growth and cost reduction of certain amino acids for many industrial applications. For example, in food applications there is huge and still growing consumption generated for glutamic acid (Glu) and glycine (Gly) as food additives and aspartic acid (Asp) and phenylalanine (Phe) as raw materials for the artificial sweetener “aspartame.” Consumption of lysine (Lys), methionine (Met), and threonine (Thr) is expanding in the animal food additives market. Cysteine (CysH) and proline (Pro) are major amino acids utilized in the flavor industry to manufacture natural flavors by Maillard reaction with sugars. Health food and pharmaceutical intermediates are other rapidly growing markets for many amino acids...
eBook - ePub- Lars Backman(Author)
- 2019(Publication Date)
- De Gruyter(Publisher)
...If going from the group with highest priority to the next in rank is clockwise, the chiral center has an R-configuration (R for rectus, Latin for right). If the order is counter-clockwise, the chiral center has an S-configuration (S for sinister, Latin for left). Thus, the α-carbon in the l -α-amino acid in Figure 3.5 has an S-configuration. In fact, all but one (cysteine) of the α-amino acid has an α-carbon in the S-configuration. 3.1 Twenty different α-amino acids Since three of the substituents bound the α-carbon are the same, it is obvious that different chemical and physical properties of each of the 20 α-amino acids depend on the side chain. The size of the side chain differs; the smallest side chain is only a proton (–H). Some side chains contain a carboxyl or an amino group, and can be ionized depending on the pH of the solvent. Some side chains are very nonpolar, whereas others are polar, which will influence their solubility in water. Some contain a conjugated ring system, giving them useful optical properties. Some side chains are branched. The 20 amino acids are usually classified as nonpolar, polar-uncharged, polar-charged or aromatic. It should be noted that some amino acids fit in more than one group; a nonpolar-uncharged amino acid may have some polar properties (Figure 3.6). 3.1.1 Nonpolar amino acids The nonpolar amino acids are glycine (Gly; G), alanine (Ala; A), valine (Val; V), leucine (Leu; L), isoleucine (Ile; I), methionine (Met; M) and proline (Pro; P). These amino acids are characterized by an aliphatic side chain of varying length whose hydrophobicity increases with increased chain length. The side chains of these amino acids cannot participate in hydrogen bonding and have a propensity to avoid contact with water. Therefore, the amino acids of this group are usually found in the interior of proteins, shielded from water contact...
eBook - ePubHandbook of Microbiology
Condensed Edition
- Allen I Laskin(Author)
- 2019(Publication Date)
- CRC Press(Publisher)
...Structures of Amino Acids Occurring in Proteins DR. D. STRUMEYER Neutral Amino Acids Aliphatic Side Chain Hydroxyl-Containing Amide-Containing Sulfur-Containing Imino Amino Acids Aromatic Acidic Amino Acids Basic Amino Aicds Amino Acid Derivatives Antibiotics...
