Chemistry
Amino Acids and Nutrition
Amino acids are the building blocks of proteins and play a crucial role in various physiological processes. They are obtained through the diet and are essential for the body's growth, repair, and maintenance. Different amino acids have specific functions and are classified as essential or non-essential based on whether the body can produce them or not.
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12 Key excerpts on "Amino Acids and Nutrition"
- Rifat Latifi, Stanley J. Dudrick(Authors)
- 2003(Publication Date)
- CRC Press(Publisher)
C hapter З Biochemistry of Amino Acids: Clinical Implications Rifat Latifi , Khawaja Aizimuddin Introduction Ajnino acids, as organic compounds, containing both an amino group and a carboxylic acid group, are the monomeric and basic constituents of all proteins. Amino acids occurring in protein are known as alpha-amino acids and have one or two empirical formulae RCH (NH+)COOH' or R-CH-(NH3)COO Beta-amino acids and gamma-amino acids also occur in nature but are not components of pro teins, and their significance is not known. This chapter reviews the basic biochemis try and physiology of amino acids and their functions as fundamental units of proteins. Their increasingly recognized and valued role in the metabolic and nutritional man agement of critically ill patients will be discussed through out this volume. Structure of Amino Acid and Proteins A protein molecule consists of amino acids held together by peptide bonds, which form a long polypeptide chain. The exact sequence of amino acids in the chain, referred to as the primary structure of the protein, is determined genetically and defines how the chain is folded into more complex conformations or shapes. A polypeptide, which is folded into a helical or pleated sheet configuration, is referred to as a secondary structure. If the sequence of amino acids is then folded into a three-dimensional configuration, a tertiary structure is created. Some pro teins have a higher level of molecular architecture known as the quaternary struc ture, in which several chains aggregate and function as a unit. The amino acid sequence and protein structure determine the nature and function of protein molecules upon which virtually every process of life depends. The folding of polypeptide chains into alpha helix and beta pleated sheets has clinical implications. The alpha helix is a rod-like structure and contains a tightly coiled polypeptide main chain.
No longer available |Learn more- Judith Brown(Author)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
8 Amino Acids The building blocks of protein are amino acids, which share the characteristic of contain-ing nitrogen. Illustration 15.4 shows an example of the basic structure of an amino acid and its nitrogen component. Twenty common amino acids (Table 15.2) form proteins, and every protein in the body is composed of unique combinations of amino acids. Nine of the 20 common amino acids are considered essential , and 11 are nonessential . The essential amino acids are called essential because the body cannot produce them or produce enough of them, so they must be provided in the diet. Healthy individuals can produce the nonessential amino acids, so we don’t require a dietary source of them. Despite the labels, all 20 amino acids are required to build and maintain protein tissues. Proteins in foods contain both essential and nonessential amino acids. Amino Acids and Protein Structure The assembly of amino acids into proteins is directed by DNA , the genetic material within each cell. Some proteins are made of only a few amino acids, while other proteins contain over 25,000. The arrangement of amino acids determines whether a protein functions as an enzyme or a hormone, or it becomes a component of red blood cells, muscle, or some other substance. Human genes are able to produce around two million proteins from the raw material provided by amino acids, and each protein performs a specific function in the body. 9 Proteins vary in size and complexity based on their role in cellular processes. They are classified by their properties as having primary, secondary, tertiary, or quaternary structures (Illustration 15.5). Proteins with primary structure consist of a linear arrangement of linked amino acids, whereas proteins with secondary structures have folded chains of amino acids. Some hormones and chemical messengers that initiate cellular processes have these structures. Tertiary structures represent the three-dimensional structure of more complex and larger proteins.
eBook - PDF- BIOTOL, B C Currell, R C E Dam-Mieras(Authors)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
15 Amino acids 2.1 Introduction and roles 16 2.2 Amino acids 17 2.3 Ionisation of amino acids 24 2.4 Identification and reactions of amino acids 37 Summary and objectives 38 16 Chapter 2 Amino acids 2.1 Introduction and roles metabolism technology importance of proteins diversity of roles of proteins Although this chapter is primarily about amino acids, we shall begin by considering proteins. The reason is that proteins are polymers constructed from amino acids. Thus by establishing the importance of proteins we can more readily appreciate why amino acids should be studied. Of all the types of compounds found in cells, proteins (from the Greek, proteios = 'first') are arguably the most important. Whilst it is true that deoxyribonucleic acid (DNA) holds the genetic information for the cell, without proteins nothing else in the cell (including DNA) would be made. In this and the next two chapters, we are going to explore proteins and nucleic acids, in order to establish some fundamental properties of these molecules. We will see how the structure of proteins is responsible for their shapes and properties: these in turn determine their uses or functions. Thus understanding the structure of biological molecules is vital for a thorough understanding of what they can do. By studying the functional properties of proteins and the roles they perform in cells, as well as by obtaining insights into how cells carry out and regulate chemical processes ('metabolism'), we may also identify how we could use proteins. This will introduce you to the idea of using cells or parts of cells to accomplish processes and show you how technology is now applicable to biology. Proteins are present in large quantities in cells. They typically constitute about 50% of the dry mass of cells. Their importance is in part a result of the enormous variety of structures (and hence properties) which is possible through the manner of their construction.
eBook - PDFHandbook of Food Analysis
Volume 1: Physical Characterization and Nutrient Analysis
- Leo M.L. Nollet(Author)
- 2004(Publication Date)
- CRC Press(Publisher)
5 Amino Acids M. Concepcio ´n Aristoy and Fidel Toldra ´ Instituto de Agroquı´mica y Tecnologı´a de Alimentos (CSIC), Valencia, Spain I. INTRODUCTION Proteins have many functions in the organism and constitute key compounds for survival of animals and humans. Proteins are naturally constituted by 20 amino acids, which act as basic components of the polymeric structure. Once proteins are ingested, amino acids are released by enzymatic digestion and absorbed into the body. So, protein quality strongly depends on its amino acid content and digestibility (1). Amino acids participate in many biochemical pathways for growth, maintenance, and metabolic activity of cells and organs and their requirements vary, depending on the stage of life (2). However, the quality of proteins may be affected by processing and storage (3,4). Thus, knowledge of the amino acid profile and the limiting amino acids in a protein is very important not only to check the quality of that protein, but also to improve the nutritional quality by supplementation with the required amino acids. Essential amino acids (listed in Table 1 ) cannot be synthesized in adult humans and must be supplied in the diet. Histidine is also essential for infants. The rest of natural amino acids are considered as nonessential (see Table 2 ) because they are efficiently synthesized in the body. There is a third group of amino acids, usually not present in proteins but with significant roles in foods (see Table 3 ). The molecular mass and structure of all these amino acids are compiled in Tables 1 , 2 , and 3 . All amino acids, except proline, contain one primary amino group (-NH 2 ) in the position in relation to the carboxy group (-COOH). Each amino acid has a characteristic side chain (R group), which has a strong influence on its physicochemical properties.
eBook - PDFVisualizing Nutrition
Everyday Choices
- Mary B. Grosvenor, Lori A. Smolin(Authors)
- 2017(Publication Date)
- Wiley(Publisher)
Amino Acid Structure Each amino acid consists of a central carbon atom that is bound to a hydrogen atom; an amino group, which contains nitrogen; an acid group; and a side chain (Figure 6.2). The nitrogen in amino acids distinguishes protein from carbohydrate and fat; all three contain carbon, hydrogen, and oxygen, but only pro- tein contains nitrogen. The side chains of amino acids vary in size and structure; they give different amino acids their unique properties. Nine of the amino acids needed by the adult human body must be consumed in the diet because they cannot be made in the body (see Figure 6.2). If the diet is deficient in one or more of these essential amino acids (also called indispensable amino acids), the body cannot make new proteins without breaking down existing proteins to provide the needed amino acids. The other 11 amino acids that are commonly found in protein are nonessential, or dispensable, amino acids because they can be made in the body. Under certain conditions, some of the nonessential amino acids cannot be synthesized in sufficient amounts to meet the body’s needs. These are therefore referred to as conditionally essential amino acids. For example, the amino acid tyrosine can be made in the body from the essen- tial amino acid phenylalanine. In individuals who have the inherited disease phenylketonuria (PKU), phenylalanine cannot be converted into tyrosine, so tyrosine is an essential amino acid for these individuals (see What a Scientist Sees: Phenylketonuria). essential , or indispensable, amino acid An amino acid that cannot be synthesized by the body in sufficient amounts to meet its needs and therefore must be included in the diet. FIGURE 6.2 Amino acids All “amino” “acids” have a similar structure that includes an amino group and an acid group, giving them their name, but each has a different side chain. Of the 20 amino acids in proteins, 9 are considered dietary essentials because they cannot be made in the body.
eBook - PDF- Mary B. Grosvenor, Diana Bedoya(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
amino acids The building blocks of proteins. Each con- tains an amino group, an acid group, and a unique side chain. 1. Which is higher in protein, an egg or a 250-g serving of rice? 2. What nutrients are plentiful in meat and milk? In grains and legumes? Animal versus plant proteins • Figure 6.1 Ask Yourself Why might a diet high in animal protein increase the risk of heart disease? Dietary protein Aspartame Phenylalanine Tyrosine Phenylketonuria Normal metabolism Phenylketones Toxic to the brain Reaction blocked Urbano Delvalle/Time Life Pictures/Getty Images Phenylketonurics: Contains phenylalanine 167 The Structure of Amino Acids and Proteins LEARNING OBJECTIVES hat do the proteins in a lamb chop, a kidney bean, and your thigh muscle have in common? They are all constructed of amino acids linked together to form one or more folded, chain- like strands. Twenty amino acids are commonly found in proteins. Each kind of protein contains a different number, combination, and sequence of these amino acids. These dif- ferences give specific proteins their unique functions in liv- ing organisms and their unique characteristics in foods. Amino Acid Structure Each amino acid consists of a carbon atom that is bound to a hydrogen atom; an amino group, which contains nitro- gen; an acid group; and a side chain (Figure 6.3a). The nitrogen in amino acids distinguishes protein from carbo- hydrates and lipids; all three contain carbon, hydrogen, and oxygen, but only protein contains nitrogen. This qual- ity also makes it inefficient for the body to use protein for W 1. Describe the general structure of an amino acid and of a protein. 2. Distinguish between essential and nonessential amino acids. 3. Discuss how the order of amino acids in a poly- peptide chain affects protein structure. 4. Explain how a protein’s structure is related to its function. energy, as the body first needs to eliminate the nitrogen- containing group before the protein can be metabolized.
No longer available |Learn more- Sharon Rady Rolfes, Kathryn Pinna, Ellie Whitney(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
172 Chapter 6 6-1 The Chemist’s View of Proteins LEARN IT Recognize the chemical structures of amino acids and proteins. Chemically, proteins contain nitrogen (N) atoms in addition to the same atoms as carbohydrates and lipids—carbon (C), hydrogen (H), and oxygen (O). These nitrogen atoms give the name amino (nitrogen containing) to the amino acids that make the links in the chains of proteins. Amino Acids All amino acids have the same basic structure—a central carbon (C) atom with a hydrogen atom (H), an amino group (NH 2 ), and an acid group (COOH) attached to it. Remember, however, that carbon atoms must have four bonds, so a fourth attachment is necessary. This fourth site distinguishes each amino acid from the others. Attached to the central carbon at the fourth bond is a distinct atom, or group of atoms, known as the side group or side chain (see Figure 6-1). Unique Side Groups The side groups on the central carbon vary from one amino acid to the next, making proteins more complex than either carbohydrates or lip-ids. A polysaccharide (starch, for example) may be several thousand units long, but each unit is a glucose molecule just like all the others. A protein, on the other hand, is made up of about 20 different amino acids, each with a different side group. Table 6-1 lists the amino acids most common in proteins.* The simplest amino acid, glycine, has a hydrogen atom as its side group. A slightly more complex amino acid, alanine, has an extra carbon with three hydrogen atoms. Other amino acids have more complex side groups (see Figure 6-2 for examples). Thus, although all amino acids share a common structure, they differ in size, shape, electrical charge, and other characteristics because of differences in these side groups. Nonessential Amino Acids More than half of the amino acids are nonessential, meaning that the body can synthesize them for itself. Proteins in foods usually deliver these amino acids, but it is not essential that they do so.
eBook - PDFVisualizing Nutrition
Everyday Choices
- Mary B. Grosvenor, Lori A. Smolin(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
contain carbon, hydrogen, and oxygen, but only protein contains nitrogen. The side chains of amino acids vary in size and struc- ture; they give different amino acids their unique properties. Nine of the amino acids needed by the adult human body must be consumed in the diet because they cannot be made in the body (see Figure 6.2). If the diet is deficient in one or more of these essential amino acids (also called indispensable amino acids), the body cannot make new proteins without breaking down existing proteins to provide the needed amino acids. The other 11 amino acids that are commonly found in protein are nonessential, or dispensable, amino acids because they can be made in the body. Under certain conditions, some of the nonessential amino acids cannot be synthesized in sufficient amounts to meet the body’s needs. These are therefore referred to as conditionally essential amino acids. For example, the amino acid tyro- sine can be made in the body from the essential amino acid phenylalanine. In individuals who have the inherited disease phenylketonuria (PKU), phenylalanine cannot be con- verted into tyrosine, so tyrosine is an essential amino acid for these individuals (see What a Scientist Sees: Phenylketonuria and Diet Soda). Protein Structure To form proteins, amino acids are linked together by pep- tide bonds, which join the acid group of one amino acid to the amino group of another amino acid (Figure 6.3). Many amino acids bonded together constitute a polypeptide. A protein is made up of one or more polypeptide chains that are folded into three-dimensional shapes. The order and chemical properties of the amino acids in a polypeptide determine its final shape because the folding of the chain occurs in response to forces that attract or repel amino acids from one another or from water.
eBook - PDF- Robert E.C. Wildman, Denis M. Medeiros(Authors)
- 2014(Publication Date)
- CRC Press(Publisher)
6 Protein The name protein is derived from the Greek term proteos, which means primary or to take place first. Protein was first discovered in the early 19th century, at which time scien tists described it as a nitrogen-containing part of food essential to life. While the elemental composition of the other energy nutrients is limited to carbon, oxygen, and hydrogen, pro tein also contains nitrogen (N) as well as sulfur (S). About one half of the dry weight of a typical human cell is attributed to protein. Some of the most significant roles for proteins are as structural components, contractile filaments, antibodies for immune responses, transporters, neurotransmitters, hormones, and enzymes. Amino Acids Proteins are composed of amino acids, many of which also have significant biological func tions or are used to make other important molecules such as neurotransmitters and hor mones. While approximately 140 types of amino acids are known to exist in nature, a much lower number of amino acids are commonly found as constituents of proteins. Only 20 amino acid are genetically coded, via mRNA. Human proteins also contain modifications of a few of these amino acids (i.e., hydroxylated amino acids); however, the modification takes place after the protein is initially synthesized. Said another way, they are posttrans- lational modifications of amino acids. Table 6.1 presents the amino acids found in human proteins along with other amino acids found in the human body that are not part of proteins. A common characteristic of amino acids found in proteins is that they have an asymmet ric or alpha (a) carbon, which has attached to it an amino group, a carboxyl group, and a hydrogen atom. The fourth entity attached to the asymmetric carbon is unique from one amino acid to the next (Figure 6.1). This feature has been called the R group or side group. Glycine is the most simple of these amino acids, as its side group is merely a hydro gen atom.
- Michael EJ Lean(Author)
- 2006(Publication Date)
- CRC Press(Publisher)
Those amino acids marked with the letter ‘E’ in Table 10.1 are known as essential (or indispensable) amino acids, meaning either that they cannot be made by the body or that they cannot be made fast enough to meet the body’s needs. Such amino acids must always be supplied by the diet. Eight amino acids are essential for adults and a further two – arginine and histidine – are essential for infants. During illness, the capacity for amino acid synthesis may be reduced so that other amino acids become ‘essential’. For example, glycine may be required from the diet during ‘conditioned essentiality’ as a result of illness, especially in infancy. Properties of amino acids Amino acids are white crystalline substances that are soluble to some extent in water but which are mostly insoluble in organic solvents. The amino group, as its name suggests, is related to ammonia and like ammonia it has basic characteristics, while the carboxyl group is acidic. The combination of an amino group and a carboxyl group in the same mol-ecule results in it being able to act as an acid or a base; such a substance is said to be amphoteric. The formulae in Table 10.1 show the arrange-ment of covalent bonds in amino acids but they CH 3 COOH CH 2 NH 2 COOH CHRNH 2 COOH Acetic acid Glycine General formula H H 2 N C C H OH O H H 2 N C C R OH O H H C C H OH O 134 Amino acids and proteins do not show the ionic character which amino acids display in solution. In solution amino acids may be more correctly represented as follows: This formula shows the ionic character of an amino acid and that it contains both a positive and a negative group. Amino acids are weak electrolytes and they ionize according to the pH of the system. We can represent this ionization as: NH 3 CH R COO NH 3 NH 3 NH 2 CH R R R CH CH COOH COO COO Positive ion Negative ion Zwitterion acid alkali H H Table 10.1 Structure of amino acids, H 2 NCHRCOOH.
eBook - PDFNutrition
Science and Applications
- Lori A. Smolin, Mary B. Grosvenor(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
206 CHAPTER 6 Proteins and Amino Acids (Figure 6.2). Different side chains give specific prop- erties to individual amino acids. Of the 20 amino acids commonly found in pro- tein, 9 cannot be made by the adult human body. These amino acids, called essential or indispens- able amino acids, must be consumed in the diet (see Figure 6.2). If the diet is deficient in one or more of these amino acids, new proteins containing them cannot be made without breaking down other body proteins to provide them. The 11 nonessential or dispensable amino acids can be made by the human body and are not required in the diet. When the diet does not provide enough of the nonessen- tial amino acids, most can be made by the pro- cess of transamination, in which an amino group from one amino acid is transferred to a carbon- containing molecule to form a different amino acid (Figure 6.3). Some amino acids are conditionally essential; that is, they are essential only under cer- tain conditions. For example, the conditionally essential amino acid tyrosine can be made in the body from the essential amino acid phenylalanine. If phenylalanine is in short supply, tyrosine cannot be made and becomes essential in the diet. Likewise, the amino acid cyste- ine is essential only when the essential amino acid methionine is in short supply or cannot be converted to cysteine. Other amino acids may be essential at certain times of life, such as premature infancy, or due to certain conditions, such as metabolic abnormalities or phys- ical stress. Protein Structure To form proteins, amino acids are linked together by peptide bonds, which are the linkages that form between the acid group of one amino acid and the nitrogen atom of the next amino acid (Figure 6.4). When two amino acids are linked with a peptide bond, the molecule formed is called a dipeptide; when three amino acids are linked, they form a tripeptide. Many amino acids bonded together constitute a polypeptide.
eBook - PDF- Sharma, Dipiti(Authors)
- 2021(Publication Date)
- Daya Publishing House(Publisher)
Acid is a byproduct of several chemical reactions that occur in the body. Normal cell functioning, such as enzyme activity, can occur only when the pH remains within a small range. Excess acid can disrupt normal body functioning and in severe cases result in coma or death. Proteins buffer this acid until it can be removed from the body by the kidneys or lungs. 5. Forming Hormones, Enzymes, and Neurotransmitters Hormones act as messengers inthe body and aid in regulatory functions, such as controlling the metabolic rate and theamount of glucose taken up from the bloodstream. Amino acids are required for the synthesis of most hormones in the body. Some hormones,such as the thyroid hormones, are made from only 1 amino acid, whereas others,such as insulin, are composed of many amino acids. Cells contain thousands of enzymes that facilitate chemical reactions fundamental to metabolism. Amino acids also are required for thesynthesis of enzymes. Many neurotransmitters (released by nerve endings), dopamine and norepinephrine (synthesized from the amino acid tyrosine), and serotonin This ebook is exclusively for this university only. Cannot be resold/distributed. (synthesized from the amino acid tryptophan). 6. Contributing to Immune Function Antibodies are proteins and are key component of the immune system. Antibodies can bind toforeign proteins (called antigens) that attack the body and can avert their attack ontarget cells. In a normal, healthy individual, antibodies are very efficient in combatingthese antigens to prevent infection and disease. However, without sufficient dietary protein,the immune system lacks the substance needed to build this defense. Thus, immuneincompetence (called anergy) develops and reduces the body’s ability to fight infection.
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