550
are the perfect nutrients to meet the body’s nutritional needs. Digestible carbohydrates in bulk are present in various foods, while indigestible carbohydrates provide
a good amount of fiber with health benefits. Plant synthesizes carbohydrate (glucose) from carbon dioxide and water, by harnessing the solar energy. These glucose
molecules are then utilized to make other larger ‘slow–releasing’ carbohydrates and
smaller ‘fast–releasing’ carbohydrates (Gibney et al. 2009; Mahan and Raymond
2016; Titchenal et al. 2018). The simpler fast–releasing carbohydrates like monosaccharides and disaccharides stimulate the sweetness taste sensation, which is the
most sensitive of all taste sensations. Some carbohydrates are much sweeter than the
others. For example, fructose tops in the sweetness value.
25.2.1.3 Proteins and Amino Acids
Proteins are macromolecules composed of chains of subunits known as amino acids.
Food sources of proteins include meats, dairy products, seafood, and a variety of
different plant–based foods, most notably soy. Proteins provide structure to bones,
muscles and skin, and play a role in conducting most of the chemical reactions that
take place in the body (Mahan and Raymond 2016; Titchenal et al. 2018; Ribarova
2018). In each amino acid, amino group and a carboxylic acid group are attached to
the structurally different cyclic/acyclic/alkyl/aryl moiety. Although structure of the
twenty amino acids is unique, there are some chemical likenesses among them and
are therefore, classified as non–polar, polar, acidic, basic, and neutral.
There are 20 different L–amino acids, and all are required to make different proteins present in the body. Eleven of these (viz. alanine, arginine, asparagine, aspartic
acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine) are called
nonessential amino acids as the body can synthesize them. The remaining nine (viz.
histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine) are called essential amino acids as these cannot be synthesized in the
body and must be obtained from the diet. The nutritional value of a protein depends
on the type and quantity of amino acids contained in them. Thus, a protein structure
is organized into four different structural levels such as primary, secondary, tertiary,
and quaternary.
The first level is the one–dimensional sequence of amino acids that is held
together by peptide bonds. They can be branched, coiled, fibrous, or globular, but
their conformation is much more random and is not organized by their sequence of
monomers. The second level of protein structure is dependent on the chemical interactions between amino acids, which cause the protein to fold into a specific shape,
such as a helix (coiled spring shape) or sheet. The third level of protein structure is
three–dimensional. As the different side chains of amino acids chemically interact,
they either repel or attract each other, resulting in the folded structure. Thus, the
specific sequence of amino acids in a protein directs the protein to fold into a specific, organized shape. The fourth level of structure is achieved when protein
K. Sharma et al.
are the perfect nutrients to meet the body’s nutritional needs. Digestible carbohydrates in bulk are present in various foods, while indigestible carbohydrates provide
a good amount of fiber with health benefits. Plant synthesizes carbohydrate (glucose) from carbon dioxide and water, by harnessing the solar energy. These glucose
molecules are then utilized to make other larger ‘slow–releasing’ carbohydrates and
smaller ‘fast–releasing’ carbohydrates (Gibney et al. 2009; Mahan and Raymond
2016; Titchenal et al. 2018). The simpler fast–releasing carbohydrates like monosaccharides and disaccharides stimulate the sweetness taste sensation, which is the
most sensitive of all taste sensations. Some carbohydrates are much sweeter than the
others. For example, fructose tops in the sweetness value.
25.2.1.3 Proteins and Amino Acids
Proteins are macromolecules composed of chains of subunits known as amino acids.
Food sources of proteins include meats, dairy products, seafood, and a variety of
different plant–based foods, most notably soy. Proteins provide structure to bones,
muscles and skin, and play a role in conducting most of the chemical reactions that
take place in the body (Mahan and Raymond 2016; Titchenal et al. 2018; Ribarova
2018). In each amino acid, amino group and a carboxylic acid group are attached to
the structurally different cyclic/acyclic/alkyl/aryl moiety. Although structure of the
twenty amino acids is unique, there are some chemical likenesses among them and
are therefore, classified as non–polar, polar, acidic, basic, and neutral.
There are 20 different L–amino acids, and all are required to make different proteins present in the body. Eleven of these (viz. alanine, arginine, asparagine, aspartic
acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine) are called
nonessential amino acids as the body can synthesize them. The remaining nine (viz.
histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine) are called essential amino acids as these cannot be synthesized in the
body and must be obtained from the diet. The nutritional value of a protein depends
on the type and quantity of amino acids contained in them. Thus, a protein structure
is organized into four different structural levels such as primary, secondary, tertiary,
and quaternary.
The first level is the one–dimensional sequence of amino acids that is held
together by peptide bonds. They can be branched, coiled, fibrous, or globular, but
their conformation is much more random and is not organized by their sequence of
monomers. The second level of protein structure is dependent on the chemical interactions between amino acids, which cause the protein to fold into a specific shape,
such as a helix (coiled spring shape) or sheet. The third level of protein structure is
three–dimensional. As the different side chains of amino acids chemically interact,
they either repel or attract each other, resulting in the folded structure. Thus, the
specific sequence of amino acids in a protein directs the protein to fold into a specific, organized shape. The fourth level of structure is achieved when protein
K. Sharma et al.