Which Of The Following Makeup Part Of The Amino Acid Structure?

Amino Acids

Amino acids (AA) are fourth compounds of carbon, hydrogen, oxygen and nitrogen and are the basic components of human proteins.

From: Nutraceuticals , 2016

Amino Acids

S. Maloy , in Brenner's Encyclopedia of Genetics (Second Edition), 2013

Abstract

Amino acids are a class of important biomolecules that contains both amino groups (−NH _three ⁺), carboxylate groups (−COO^‒), and a side chain (–R). Although amino acids with hundreds of unlike side chains have been identified or synthesized, only twenty amino acids are mutual building blocks of proteins. Except for glycine, all of the α-amino acids have four different substituents attached to the α-carbon and are therefore chiral molecules. In improver to subunits of proteins, amino acids have many other functions as well, including osmoregulation (proline), neurotransmitters (gamma-aminobutyric acid), metabolic intermediates (ornithine and citrulline), and inhibitors (dehydroproline).

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AMINO ACIDS

S.M. Lunte , in Encyclopedia of Belittling Science (2nd Edition), 2005

Pulsed amperometric detection (PAD)

Amino acids are not more often than not considered to exist electrochemically active because products of the oxidation accrue on the electrode surface and forbid it from participating in any further electrochemical processes. This problem can be overcome if PAD is employed. Amino acids are more often than not detected using a platinum electrode under alkaline conditions (0.25  mol   50⁻¹ NaOH) using a triple-pulse waveform with E ₁, Due east ₂, and E ₃ at 0.50, −0.89, and 0.70   V, respectively. Due to the basic conditions required for the detection of amino acids, a base-stable anion-substitution column must be employed. Detection limits of 50   pmol accept been obtained for phenylalanine and methionine using this technique.

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Convenance Genetics and Biotechnology

P.J. Lea , R.A. Azevedo , in Encyclopedia of Applied Plant Sciences (2d Edition), 2017

Introduction

Amino acids are the major nitrogen-containing compounds of plants and are the edifice blocks of proteins. There are xx different amino acids normally incorporated into proteins, although they may be subject to alteration afterward, by enzyme reactions such equally phosphorylation, methylation, and acetylation. In addition to those in protein, over 300 additional amino acids have been isolated and characterized from plants. With the arrival of fifty-fifty more sensitive analytical techniques, this number is likely to increase. These amino acids may exist nowadays in low concentrations and play a vital role every bit an intermediate in a biosynthetic pathway, e.g., ornithine, homoserine, or cystathionine. In contrast they may human action as a major storage class of nitrogen, e.g., canavanine in the seed of Canavalia ensiformis, or may exist formed in high amounts in response to an external stress, e.g., γ-aminobutyrate. It is possible that some of these nonprotein amino acids may serve every bit insecticidal or fungicidal agents.

Humans and monogastric animals are not able to synthesize the following nine amino acids: lysine, threonine, methionine, phenylalanine, tryptophan, isoleucine, leucine, valine, and histidine. These are termed 'essential' and must exist supplied in the diet. They are, withal, able to convert methionine to cysteine and phenylalanine to tyrosine, provided they are available. Plants are able to synthesize all 20 protein amino acids, and these may exist classified into 'families' by the pathways that are involved. These pathways are frequently subject field to very complex and tight regulation to prevent the wastage of energy and the key nutrients carbon, nitrogen, and sulfur. It is interesting to note that the enzymes involved in the synthesis of the 'essential' amino acids are normally located within the chloroplasts of the leaves or the plastids of the nonphotosynthetic organs, such as the roots or seeds.

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Amino Acids

N.V. Bhagavan , Chung-Eun Ha , in Essentials of Medical Biochemistry (Second Edition), 2015

Electrolyte and Acid–Base of operations Properties

Amino acids are ampholytes; i.e., they contain both acidic and basic groups. Free amino acids can never occur as nonionic molecules. Instead, they exist equally neutral zwitterions that contain both positively and negatively charged groups. Zwitterions are electrically neutral and so exercise not drift in an electric field. In an acidic solution (beneath pH 2.0), the predominant species of an amino acid is positively charged and migrates toward the cathode. In a bones solution (in a higher place pH 9.vii), the predominant species of an amino acrid is negatively charged and migrates toward the anode.

The isoelectric point (pI) of an amino acid is the pH at which the molecule has an average net accuse of zero and therefore does non migrate in an electric field. The pI is calculated by averaging the pK′ values for the two functional groups that react equally the zwitterion becomes alternately a monovalent cation or a monovalent anion.

At physiological pH, monoaminomonocarboxylic amino acids, eastward.g., glycine and alanine, exist equally zwitterions. That is, at a pH of half dozen.9–7.4, the α-carboxyl group (pK′=2.4) is dissociated to yield a negatively charged carboxylate ion (COO⁻), while the α-amino group (pK′=.vii) is protonated to yield an ammonium group (NH₃ ⁺). The pK′ value of the α-carboxyl group is considerably lower than that of a comparable aliphatic acid, due east.g., acetic acid (pK′=4.6). This stronger acerbity is due to electron withdrawal by the positively charged ammonium ion and the consistent increased tendency of a carboxyl hydrogen to dissociate as an H⁺. The α-ammonium group is correspondingly a weaker acid than an aliphatic ammonium ion, e.thousand., ethylamine (pK′=9.0), because the anterior effect of the negatively charged carboxylate anion tends to forbid dissociation of H⁺. The titration contour of glycine (Figure three.six) is nearly identical to the profiles of all other monoaminomonocarboxylic amino acids with nonionizable R-groups (Ala, Val, Leu, Ile, Phe, Ser, Thr, Gln, Asn, Met, and Pro).

Figure 3.6. Titration profile of glycine, a monoaminomonocarboxylic acrid.

The titration of glycine has the following major features. The titration is initiated with glycine hydrochloride, Cl⁻(H₃ ⁺NCH₂COOH), which is the fully protonated grade of the amino acid. In this form, the molecule contains two acidic functional groups; therefore, 2 equivalents of base are required to completely titrate i   mol of glycine hydrochloride. In that location are two pK′ values: $\mathrm{pK}{\prime }_1$ due to reaction of the carboxyl group and $\mathrm{pK}{\prime }_{\mathrm{ii}}$ due to reaction of the ammonium grouping. Addition of 0.v eq of base of operations to ane   mol of glycine hydrochloride raises the pH ii.34 ( $\mathrm{pK}{\prime }_1$ ), whereas addition of 1.five eq further increases the pH to 9.66 ( $\mathrm{pK}{\prime }_2$ ). At low pH values (e.g., 0.4), the molecules are predominantly cations with one positive accuse; at pH values of 5–seven, most molecules accept a internet charge of aught; at high pH values (e.g., eleven.7), all of the molecules are essentially anions with ane negative charge. The midpoint between the two pK′ values [i.e., at pH=(2.34+9.66)/2=6.0] is the pI. Thus, pI is the arithmetic mean of $\mathrm{pK}{\prime }_1$ and $\mathrm{pK}{\prime }_2$ values and the inflection point between the two segments of the titration contour.

The buffering capacities of weak acids and weak bases are maximal at their pK′ values. Thus, monoamino monocarboxylic acids showroom their greatest buffering capacities in the two pH ranges near their two pK′ values, namely, pH 2.3 and pH 9.vii (Figure iii.6). Neither these amino acids nor the α-amino or α-carboxyl groups of other amino acids (which take similar pK′ values) have pregnant buffering chapters in the neutral (physiological) pH range. The only amino acids with R-groups that have buffering capacity in the physiological pH range are histidine (imidazole; pK′=6.0) and cysteine (sulfhydryl; pK′=8.iii). The pK and pI values of selected amino acids are listed in Tabular array 3.2. The pK′ values for R-groups vary with the ionic surroundings.

Table iii.2. pK′ and pI Values of Selected Free Amino Acids at 25°C*

Amino Acid	$\mathbf{pK}{\prime }_{\mathrm{one}}$ (α-COOH)	$\mathbf{pK}{\prime }_2$	$\mathbf{pK}{\prime }_{\mathrm{iii}}$	pI
Alanine	two.34	$9.69(\mathrm{\beta }-{\mathrm{NH}}_3^{+})$		half-dozen.00
Aspartic acid	2.09	3.86 (γ-COOH)	$9.82(\alpha -{\mathrm{NH}}_{\mathrm{three}}^{+})$	$2.98\left(\frac{\mathrm{pK}{\prime }_1+\mathrm{pK}{\prime }_2}{\mathrm{ii}}\right)$
Glutamic acid	2.nineteen	4.25 (γ-COOH)	$9.67(\alpha -{\mathrm{NH}}_3^{+})$	$3.22\left(\frac{\mathrm{pK}{\prime }_1+\mathrm{pK}{\prime }_{\mathrm{ii}}}{2}\right)$
Arginine	2.17	$9.04(\alpha -{\mathrm{NH}}_3^{+})$	12.48 (Guanidinium)	$10.76\left(\frac{\mathrm{pK}{\prime }_2+\mathrm{pK}{\prime }_{\mathrm{three}}}{2}\right)$
Histidine	1.82	half dozen.00 (Imidazolium)	$9.17({\mathrm{NH}}_{\mathrm{three}}^{+})$	$7.59\left(\frac{\mathrm{pK}{\prime }_2+\mathrm{pK}{\prime }_3}{2}\right)$
Lysine	ii.eighteen	$8.95(\alpha -{\mathrm{NH}}_3^{+})$	$10.53(\epsilon -{\mathrm{NH}}_{\mathrm{iii}}^{+})$	$9.74\left(\frac{\mathrm{pK}{\prime }_2+\mathrm{pK}{\prime }_{\mathrm{iii}}}{\mathrm{two}}\right)$
Cysteine	1.71	eight.33 (SH)	$\mathrm{ten.78}(\alpha -{\mathrm{NH}}_3^{+})$	$5.02\left(\frac{\mathrm{pK}{\prime }_1+\mathrm{pK}{\prime }_{\mathrm{two}}}{2}\right)$
Tyrosine	2.20	$\mathrm{nine}.11(\alpha -{\mathrm{NH}}_3^{+})$	10.07 (Phenol OH)	$\mathrm{five.66}\left(\frac{\mathrm{pK}{\prime }_1+\mathrm{pK}{\prime }_2}{\mathrm{ii}}\right)$
Serine	2.21	$9.15(\alpha -{\mathrm{NH}}_3^{+})$	13.6 (Alcohol OH)	$5.68\left(\frac{\mathrm{pK}{\prime }_1+\mathrm{pK}{\prime }_2}{2}\right)$

*

The pK′ values for functional groups in proteins may vary significantly from the values for costless amino acids.

The pK′ values for functional groups in proteins may vary significantly from the values for gratuitous amino acids. The R-groups are ionized at physiological pH and have anionic and cationic groups, respectively.

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Amino Acids

Edward K. Neilan , Vivian E. Shih , in Encyclopedia of the Neurological Sciences, 2003

Structure of Amino Acids

The term amino acid usually refers to an α-aminocarboxylic acrid in which the α carbon atom next to a carboxylic acid moiety (-COOH) carries three other substituents: an amino grouping (-NH₂), a hydrogen cantlet (-H), and a variable side chain conventionally symbolized as "-R" (Fig. 1). These iv substituents are arranged around the α carbon in a tetrahedral mode. Two nonoverlapping arrangements are possible. By convention, these optically active, mirror-image stereoisomers are designated the l and d forms. Except in the case of glycine, in which R is a second hydrogen atom, the four substituents are different, making the α carbon atom a centre of chirality.

Effigy one. The construction of amino acids. Most are optically active and exist equally mirror-epitome l- or d-isomers.

Simply the l -isomers of amino acids are commonly found in proteins. The biosynthetic pathways that produce amino acids are stereospecific, and most generate only 50-isomers. Therefore, l-isomers are present at much college concentrations in homo tissues and actual fluids. d-Amino acids, although less common than l-amino acids, practise take some important roles in nature. For example, they have long been known to exist components of the prison cell walls of certain bacteria. Recently, d-aspartate and d-serine accept been institute to exist in significant concentrations in mammalian brains. In fact, evidence suggests that d-serine acts as a genuine neurotransmitter.

When dissolved in aqueous solutions at neutral pH, the carboxylic acid groups of amino acids are deprotonated, while their amino groups are protonated (Fig. two). This makes each amino acrid molecule a dipolar ion or zwitterion (from the German language zwitter, meaning mongrel).

Figure 2. Amino acids in solution are dipolar ions.

Twenty amino acids are commonly plant in proteins (Fig. 3). Most of these have neutral side bondage. Notwithstanding, the carboxylic acrid groups in the side chains of aspartate and glutamate are deprotonated and negatively charged at physiological pH, whereas the side chains of arginine and lysine are protonated and positively charged. The imidazole ring in histidine'due south side chain has a pM of vi.0 and may either exist positively charged or neutral in physiological solutions, depending on the verbal pH and on local interactions with surrounding atoms.

Figure 3. The 20 amino acids commonly found in proteins. Those which are charged, hydrophilic, or hydrophobic are indicated, as are the standard iii-letter and single-letter abbreviations.

The sizes, shapes, and chemic properties of the amino acid side chains in a poly peptide determine that poly peptide'south unique three-dimensional folding blueprint and its specific functions. One major determinant of protein folding is the hydrophobicity of the amino acid side bondage. Asparagine, glutamine, and the five charged amino acids are hydrophilic. Patterns of protein folding that exit these amino acids exposed to water are thermodynamically favored. 5 amino acids—phenylalanine, methionine, isoleucine, leucine, and valine—are hydrophobic. They are generally either cached within protein interiors or exposed to lipids along the transmembrane segments of integral membrane proteins. The eight remaining amino acids take intermediate affinities for h2o and may hands occupy a variety of positions within proteins.

The properties of a few amino acids have especially important consequences for protein folding and function. For example, proline is unique among the amino acids because it is a secondary amine rather than a master amine. The nitrogen atom of proline is part of a five-membered ring construction. This prevents rotation betwixt the nitrogen cantlet and the adjacent α carbon atom. Therefore, the occurrence of proline in a polypeptide chain tends to cause a "curve" in its three-dimensional course. Cysteine is too unique amid amino acids. The sulfhydral group (-SH) of one cysteine may form a disulfide bond (-South–Southward-) with another cysteine, thus creating a covalent bond between two different proteins or betwixt ii unlike points forth same polypeptide. These disulfide bonds are often essential to the proper folding and function of the proteins that comprise them. Finally, the "catalytic" atoms crucial to enzymatic activity are oft provided past the side chains of specific amino acids.

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Amino Acids

N.Five. BHAGAVAN , in Medical Biochemistry (Fourth Edition), 2002

Unusual Amino Acids

Several L-amino acids have physiological functions as free amino acids rather than equally constituents of proteins. Examples are as follows:

1

β-Alanine is part of the vitamin pantothenic acid.

2

Homocysteine, homoserine, ornithine, and citrulline are intermediates in the biosynthesis of certain other amino acids.

3

Taurine, which has an amino group in the β-carbon and a sulfonic acrid group instead of COOH, is present in the CNS and equally a component of certain bile acids participates in digestion and absorption of lipids in the gastrointestinal tract.

iv

y-Aminobutyric acid is an inhibitory neurotransmitter.

5

Hypoglycin A is present in unripe akee fruit and produces astringent hypoglycemia when ingested.

6

Some D-amino acids are found in polypeptide antibiotics, such as gramicidins and bacitracins, and in bacterial prison cell wall peptides.

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Amino Acids

L.B. Willis , ... A.J. Sinskey , in Encyclopedia of Genetics, 2001

Sources and Uses of Amino Acids

Plants and many bacteria synthesize all 20 of the amino acids listed in Effigy 2. Amino acids are synthesized from a variety of primary metabolites in living cells. Yet, vertebrates, including humans, are merely able to manufacture a subset of these amino acids. Hence they must obtain the remainder of their amino acids from their diet. Amino acids that must be obtained in this manner are known equally essential amino acids (Figure 2). Since proteins are equanimous of amino acids, diets that are rich in protein are more probable to incorporate sufficient amounts of each of the essential amino acids to forestall whatsoever deficiencies.

In animal feeds, all the same, where the bulk of the protein present may come from a single source such as grain, imbalances in the individual essential amino acids tin occur. For case, corn (maize) provides the majority of protein in feed for livestock. Notwithstanding the protein found in normal field corn is unduly low in lysine. To compensate, farmers routinely add lysine to creature feed to improve its nutritional value.

Amino acids are produced commercially from a variety of sources and for a diverseness of uses. For case, lysine, tryptophan, and threonine to be used as feed supplements are produced past fermentation. In these processes, genetically altered bacteria that produce more than of an amino acid than they need for their own growth excrete the excess amino acid into their growth medium. In one case the desired amino acid accumulates to a sufficient level, the bacteria tin be removed and the amino acid purified for employ straight or every bit an ingredient in feed formulations. Glutamic acid, which is often used as the flavor-enhancer monosodium glutamate (MSG), is similarly produced past microbial fermentation. Other amino acids are produced commercially by chemically hydrolyzing proteins. Thus cysteine, which is especially abundant in the protein keratin, is produced from hair.

In addition to industrial applications in animal feed, man diet, and flavor enhancers, amino acids are also important components of cosmetics and medications. Amino acids or their chemic analogs can be used as precursors for synthesis of pharmaceutical agents. Synthetic polymers of amino acids are used to encapsulate drugs so equally to assistance in their absorption or to command their release into the bloodstream. Current research into amino acids promises to yield new polymers that can be used as textile fibers, novel antibiotics to combat infectious diseases, and nutritionally enhanced plants to feed a hungry world.

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Organic Nitrogen

Northward.O.G. Jørgensen , in Encyclopedia of Inland Waters, 2009

Dissolved Free and Combined Amino Acids

Amino acids are the most studied DON compounds in freshwater. The amino acrid pool consists of truly dissolved free amino acids (DFAA), and amino acids bound in peptides, proteins, or adsorbed to inorganic and organic affair, named dissolved combined amino acids (DCAA). Concentrations of DFAA and DCAA in lakes and streams reverberate a balance between input and uptake. Concentrations of DCAA are usually college than concentrations of DFAA, as DCAA must first be degraded by enzymes to costless amino acids (DFAA) before being used past microorganisms. This means that microbial production of enzymes often volition limit the utilization of DCAA.

Concentrations of amino acids in lakes and rivers volition typically reflect the trophic status of the surroundings. The lowest concentrations (0.01–0.two   μM N for DFAA and 0.3–2.5   μM N for DCAA) occur in oligotrophic waters, while higher concentrations (upward to 1.8   μM DFAA-N and five.0   μM DCAA-N) unremarkably are constitute in eutrophic lakes and rivers. Highest concentrations within the shown ranges are found during seasons with a high biological production, while significantly lower amounts of both DFAA and DCAA occur during winter.

The highest concentrations of DFAA accept been measured in extreme lakes such as the hypersaline Antarctic Organic Lake (upward to 290   μM DFAA-N in the anoxic hypolimnion) and the alkaline soda lake Mono Lake (up to 3   μM DFAA-N). Organic Lake receives large amounts of nitrogen and phosphorus from penguins and these nutrients sustain dumbo populations of the algae Dunaliella in the lake. Mono Lake is a hypersaline, alkaline, and phosphorus-rich lake in the Sierra Nevada Mountains, California, with specialized algal populations.

Similar DFAA, some of the highest concentrations of DCAA are found in extreme lakes (up to 13   μM North in Mono Lake; no data on DCAA in Organic Lake are available), simply in humic lakes even college amounts of DCAA have been measured. In humic, Finnish lakes, the content of DCAA can vary from 5 to 25   μM N. A portion of the humic-jump amino acids is bachelor to microorganisms, but nearly of the amino acids in humic affair are resistant to bacterial deposition.

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Amino Acids: Chemistry and Classification

Guoyao Wu , in Reference Module in Nutrient Science, 2021

Abstract

Amino acids (AAs) contain both amino and acrid groups. The chemical configuration of AAs is by and large defined in reference to l- and d-glyceraldehyde. All proteinogenic (protein-creating) AAs except glycine tin can have both fifty- and d-isomers. L-AAs plus glycine are the almost abundant isomers and account for >99.9% of total AAs in humans, only some D-AAs have important physiological functions. Different AAs take different chemical properties (e.g., solubility, stability, melting points, reactions, gustation, and electrical charges). AAs tin can be classified as neutral, basic, and acidic AAs, or as aliphatic, sulfur-containing, hydroxylated, amidated, carboxylated, phosphorylated, guanidino, aromatic, imidazole, seleno, and secondary AAs.

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Amino Acids and Energy Metabolism

Kohsuke Hayamizu , in Sustained Energy for Enhanced Human Functions and Action, 2017

Glucogenic Amino Acids and Ketogenic Amino Acids

Amino acids that form pyruvic acid or any of the intermediates of the TCA cycle by catabolism are chosen glucogenic amino acids. These amino acids serve equally substrates for gluconeogenesis and therefore are used to synthesize glucose in the liver and kidneys. In dissimilarity, amino acids that course acetoacetic acid or its precursors (acetyl CoA or acetoacetyl CoA) are chosen ketogenic amino acids. Ketogenic amino acids are used to synthesize ketone bodies and fatty acids. Amongst constituent amino acids, simply leucine and lysine are exclusively ketogenic. The carbon skeletons of these amino acids are non substrates of gluconeogenesis and thus exercise not produce glucose ( Table 21.2).

Tabular array 21.2. Classification of Amino Acids by Catabolism

	Glycogenic Amino Acids	Glycogenic and Ketogenic Amino Acids	Ketogenic Amino Acids
Essential amino acids	Hys	Ile	Leu
	Met	Phe	Lys
	Thr	Trp
	Val
Nonessential amino acids	Ala	Tyr
	Arg
	Asn
	Asp
	Cys
	Glu
	Gln
	Gly
	Pro
	Ser

Threonine is sometimes classified equally both a glucogenic and ketogenic amino acid. Arginine tin exist synthesized in the urea cycle, and thus it is a nonessential amino acid in adults. However children require more arginine than is synthesized in the body; therefore it is an essential amino acid in children.

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