Amino Acids Peptides and Proteins
Amino acids are the building blocks of proteins, consisting of a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a side chain. Peptides are short chains of amino acids linked by peptide bonds, while proteins are larger, complex molecules made up of one or more polypeptide chains. These molecules play crucial roles in the structure and function of living organisms.
8 Key excerpts on "Amino Acids Peptides and Proteins"
eBook - ePub- Guoyao Wu(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
...4 Chemistry of Protein and Amino Acids The word “protein” originated from the Greek word “proteios,” meaning prime or primary (Meister 1965). A protein is a large polymer of amino acids (AAs) linked via the peptide bond (–CO–NH–). Different proteins have different chemical properties (e.g., AA sequences, molecular weights, ionic charges, three-dimensional (3D) structures, hydrophobicity, and function). The general structure of an AA is shown in Figure 4.1. There may be one or more polypeptide chains in a protein, which contains its constituents (nitrogen, carbon, oxygen, hydrogen, and sulfur atoms). A protein may be covalently bonded to other atoms and molecules (e.g., phosphates) and non-covalently attached with minerals (e.g., calcium, iron, copper, zinc, magnesium, and manganese), certain vitamins (e.g., vitamin B 6, vitamin B 12, and lipid-soluble vitamins), and/or lipids. Protein is the major nitrogenous macronutrient in foods and the fundamental component of animal tissues (Wu 2016). It has structural, signaling, and physiological functions in animals (Table 4.1). Figure 4.1 Fisher projections for configurations of AAs relative to l - and d -glyceraldehydes. The general structure of an AA in the non-ionized form is shown...
eBook - ePubBiochemistry
An Organic Chemistry Approach
- Michael B. Smith(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...12 Peptides and Proteins Polymeric chains of amino acids are peptides, and proteins are poly(peptides). Proteins are essential to living systems and the critically important proteins called enzymes catalyze processes that are essential to life. This chapter will discuss peptides, their characteristics and how they are formed. In addition, the structure and function of proteins will be discussed. 12.1 Reactions and Synthesis of α-Amino Acids Amino acids undergo several important reactions that are dominated by the amine group and/or the carboxyl group. The fact that the amine and the carboxyl react with each other complicates things, because one functional group will influence the reactivity of the other. The conversion of a simple carboxylic acid to an ester is quite easy, either by reaction of the carboxylic acid with an alcohol under acidic conditions, or by first converting the acid to an acid chloride and subsequent reaction with an alcohol. However, amines also react with acid chlorides or with esters to yield the corresponding amide. In other words, trying to form an ester in the presence of an amine may be a problem. To target one functional group in an amino acid, the other must be taken into account and usually blocked (protected) with a functional group that can be removed after the planned reaction. The carboxylic acid group of an amino acid can be converted to an ester by reaction with an alcohol in the presence of aqueous acid. Using the zwitterion form of alanine as an example, treatment with acid generates the protonated form, (1 S)-carboxyethanaminium. Subsequent reaction of aqueous ethanol and an acid catalyst converts the COOH unit to the corresponding ester of alanine. The amine unit exists as its ammonium salt in the aqueous acid medium. The amine unit of an amino acid can be functionalized...
eBook - ePub- S. P. Bhutani(Author)
- 2019(Publication Date)
- CRC Press(Publisher)
...Even in plants, where carbohydrates are more abundant as structural materials, proteins are present in those parts that are responsible for growth and reproduction. The fundamental structure of proteins is simple. Proteins are biopolymers of α-amino acids. They consist of long chains of α-amino acids bonded to each other by amide bonds also known as peptide linkages between the carboyxlic group of one amino acid with the amino group of another. Thus, proteins are high molecular weight polypeptides. Their molecular weight may range from 5000–100,000 units. A single protein molecule contains hundreds or even thousands of amino acid units. About twenty different amino acids are the building blocks of proteins. The number of different combinations, that is the number of different protein molecules that are possible, is almost infinite. 2.2 AMINO ACIDS – THE BUILDING BLOCKS OF PROTEINS We have seen above that α-amino acids are the building blocks of proteins. Hydrolysis of proteins with an acid or base yields a mixture of different amino acids. Naturally occurring proteins on hydrolysis may yield twenty-two different amino acids. These amino acids have an important structural feature in common. All are α-amino acids; i.e., the amino group is bonded to the α-carbon atom next to the carboxyl group. The simplest amino acid is glycine. All others can be derived from glycine. where the R group is different for different amino acids. With the exception of glycine, all naturally occurring amino acids have the L -configuration at the α-carbon. 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...
eBook - ePub- Raymond S. Ochs(Author)
- 2021(Publication Date)
- CRC Press(Publisher)
...The lack of rotation about the C–N bond restricts the possible three-dimensional arrangements of peptide-bonded structures. Once peptide bonds are formed, the component amine and carboxyl groups no longer have acid–base characteristics. Only the amine group at one end of the molecule and the carboxyl group at the other end are dissociable, along with the side chains (the R groups attached to the alpha carbons). Therefore, the ends of the chain are distinct: there is one amino end (the N-terminus) and a carboxyl end (the C-terminus). The polymer itself has distinctive properties, which vary with the length of the chain and the composition of the R-groups. 5.6 Peptides and Proteins Short chains of amino acids, roughly up to 25 amino acids, are called peptides ; longer chains are called proteins. The cutoff between these is somewhat arbitrary, but there is a functional difference. Peptides have flexibility in their structure, due to rotations about single bonds, a feature they share with other relatively small molecules. However, proteins have a more fixed behavior in solution as a result of intramolecular interactions. Three-dimensional structures are characteristic of other polymers, such as polysaccharides. Large molecules that occur in biological systems are called macromolecules. Two examples of peptides are both hormones that regulate blood pressure; these are diagrammed in Figure 5.15. Angiotensin II is a linear peptide, whereas vasopressin is cyclic, resulting from a bridge formed between the sulfhydryl groups of two cysteines. While the latter is thereby more constrained in its structure, both have no fixed structure in solution and change their conformation upon binding to their hormone receptors. Many peptides are formed by proteolysis extracellularly, such as in the stomach and intestine (Box 5.2). FIGURE 5.15 Angiotensin II and vasopressin. Box 5.2 Protein Digestion Proteins are converted to amino acids in a two-step process in humans...
eBook - ePubCosmetic Dermatology
Products and Procedures
- Zoe Diana Draelos, Zoe Diana Draelos(Authors)
- 2021(Publication Date)
- Wiley-Blackwell(Publisher)
...In the five years since the previous edition of this book, a number of new such peptides have been studied, developed and used for cosmetic applications and both skin and hair care benefits. In the second part, concrete examples of peptides and some proteins, in particular for the “anti‐aging” sector, are discussed before concluding with the further outlook for the future of this ingredient category. Definitions It is important to understand the differences between amino acids, peptides, and proteins. Amino acids Amino acids are the building blocks of which peptides and proteins are made. They are small molecules, with a molecular weight of 100–200 Dalton, characterized by the fact that both an amino group (NH 2) and a carboxylic acid group (COOH) are attached to the central carbon atom (α‐carbon). This carbon atom with four valencies carries furthermore one hydrogen (except for the cyclic proline) and a side chain R that varies from amino acid to amino acid, side chains by which the different amino acids are distinguished (Figure 38.1). Given this narrow definition, we can imagine a theoretically unlimited number of alpha‐amino acids by simply varying the structure of the side chains, but only 20 (e.g. alanine, proline, tyrosine, histidine, phenylalanine, lysine, glutamine …) are incorporated into peptides and proteins via the genetic code. With few exceptions, these amino acids in isolation have no specific intrinsic biological activity. Within cells, they exist in a pool from which they can be called upon to make peptides and proteins or, sometimes, biogenic amines, such as serotonin or dopamine. In the upper layers of the skin, they are part of the natural moisturizing factor (NMF) where they participate in the water holding capacity of the skin contributing to both osmolytic and hygroscopic properties...
eBook - ePub- David P. Clark(Author)
- 2009(Publication Date)
- Academic Cell(Publisher)
...All have a central carbon atom, the alpha carbon, surrounded by a hydrogen atom, an amino group (NH 2), a carboxyl group (COOH), and a variable side chain, the R-group (Fig. 3.24). Amino acids are joined together by peptide bonds (Fig. 3.25). The first amino acid in the chain retains its free amino group and this end is often called the amino - or N-terminus of the polypeptide chain. The last amino acid to be added is left with a free carboxyl group and this end is often called the carboxy - or C-terminus. Figure 3.24 General Features of Amino Acids Almost all amino acids found in proteins have the features shown in common. In glycine, the simplest amino acid, the R group is a single hydrogen atom. In proline, the R group consists of a ring structure that bonds to the nitrogen atom shown. This therefore only has a single attached hydrogen and becomes an imino group (—NH—). Figure 3.25 Formation of a Polypeptide Chain A polypeptide chain is formed as amino and carboxyl groups on two neighboring amino acids combine and eliminate water. The linkage formed is known as a peptide bond. No matter how many amino acids are added, the growing chain always has an N- or amino terminus, and a C- or carboxy terminus. alpha carbon The central carbon atom of an amino acid, to which the amino, carboxyl and R groups are attached enzyme A protein or RNA molecule that catalyses a chemical reaction peptide bond Type of chemical linkage holding amino acids together in a protein molecule polypeptide chain Polymeric chain of amino acids R-group Chemical group forming side chain of amino acid Some proteins consist of a single polypeptide chain; others contain more than one. To function properly, many proteins need extra components, called cofactors or prosthetic groups, which are not made of amino acids...
eBook - ePubWheat
Chemistry and Utilization
- Hugh Cornell, Albert W. Hoveling(Authors)
- 2020(Publication Date)
- CRC Press(Publisher)
...CHAPTER 7 Amino Acids, Peptides, and Proteins 7.0 INTRODUCTION T HE proteins form a particularly diverse group of compounds, ranging from structural proteins to key molecules such as enzymes and hormones. The proteins in wheat are also diverse in nature and include a group of enzymes as seen in Section 1.7. Proteins are found in animals and plants where they constitute a large percentage of the dry weight of cells. They form an important part of the diet and are very valuable in this respect, as they provide essential amino acids, numbering about nine. The daily requirements of most of these amino acids are about 10–14 mg/day/kg of body weight for adults, with tryptophan and threonine being 3.5 and 7 mg/day/kg, respectively, according to the FOA/WHO (1973). The requirements of total protein intake are given as 570 mg/day/kg for men and 520 mg/day/kg for women. Infants require larger quantities of essential amino acids and proteins on a per kg body-weight basis. A good guide is an intake of about 8% of the total calorie intake as protein. Higher figures than this may be detrimental to health, especially if fatty meat is a significant contributor. Proteins in the body are continuously degraded to amino acids (catabolism) and must therefore be synthesized in corresponding amounts (anabolism). These processes are quite rapid in the liver and the small intestine, whereas they are slow in the muscles and connective tissues. Nitrogen is released in the urine, mainly as urea. 7.1 AMINO ACIDS Altogether, over 20 amino acids are present in naturally occurring proteins. These are mostly of the α-amino structure and are usually of the L -configuration. In Fischer projection they are written as shown: The Fischer projection of an α-amino acid (L -configuration) shows its relationship to L -glyceraldehyde...
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...
