{"id":457,"date":"2024-04-02T18:15:31","date_gmt":"2024-04-02T18:15:31","guid":{"rendered":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/?post_type=chapter&p=457"},"modified":"2024-11-30T05:56:13","modified_gmt":"2024-11-30T05:56:13","slug":"1-6-b-chemical-constituents-of-cell-proteins","status":"publish","type":"chapter","link":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/chapter\/1-6-b-chemical-constituents-of-cell-proteins\/","title":{"raw":"1.6 b , Chemical constituents of cell -Proteins","rendered":"1.6 b , Chemical constituents of cell -Proteins"},"content":{"raw":"The next abundant constituent of cell is\u00a0 Proteins. They perform numerous functions vital to all organisms. <\/span>\r\n\r\nThese are made from amino acids <\/span>\r\n\r\nThey function as structural components of cells and subcellular entities.<\/span>\r\n\r\nThey act as sources of nutrients, as atom- and energy-storage reservoirs, and <\/span>\r\n\r\nThey are functional species such as hormones, enzymes, receptors, and transport molecules.<\/span>\r\n

Aminoacids<\/h1>\r\nThese are organic molecules .\r\n\r\nThey contain a\u00a0hydrogen atom, a\u00a0<\/span>carboxyl group<\/span>\u00a0(\u2013COOH), and an amino group (\u2013NH<\/span>2<\/sub>) and all of these are bonded to the same carbon atom, called\u00a0<\/span>\u03b1 carbon<\/span>. <\/span>\r\n\r\nThe fourth group bonded to the \u03b1 carbon varies among the different amino acids and is called a\u00a0<\/span>residue<\/span>\u00a0or a\u00a0<\/span>side chain<\/span>, represented in structural formulas by the letter\u00a0<\/span>R<\/em>. <\/span>\r\n\r\nWhen two or more amino acids combine, water molecule is removed and the two amino acids are connected by a covalent bond called the [pb_glossary id=\"489\"] Peptide bond, [\/pb_glossary] <\/strong>which is formed by the <\/span>reaction of the\u00a0<\/span>carboxylic acid<\/span> group of one amino acid molecule with the\u00a0<\/span>amine group<\/span> of another amino acid molecule. The resulting molecule is called a Peptide.<\/strong><\/span>\r\n\r\n\u00a0Prefixes are often used to specify these numbers of amino acids that join for example dipeptides<\/span>\u00a0(two amino acids),\u00a0<\/span>tripeptide<\/span>s (three amino acids) etc., <\/span>\r\n\r\nIn general <\/span>oligopeptide<\/span>s<\/strong>\u00a0are formed by joining up to approximately 20 amino acids, whereas\u00a0<\/span>polypeptide<\/span>s<\/strong>\u00a0are synthesized from up to approximately 50 amino acids.<\/span>\r\n\r\n\"Alanine\r\n

\"Proteins\"<\/a>\u00a0by\u00a0<\/span>OpenStax<\/a><\/a><\/a>\u00a0is licensed under\u00a0<\/span>CC BY 4.0<\/a><\/p>\r\nWhen the number of amino acids linked together becomes very large, or when multiple polypeptides are used as building subunits, the macromolecules that result are called\u00a0<\/strong><\/span>proteins<\/span>.<\/strong>\r\n

Protein Structure<\/h2>\r\nThe size (length) and specific amino acid sequence of a protein are major determinants of its shape, and the shape of a protein is critical to its function.<\/span>\r\n\r\nProtein structure is categorized in terms of four levels: primary, secondary, tertiary, and quaternary.<\/span>\r\n\r\n The\u00a0primary structure :<\/span><\/strong>\u00a0<\/strong>is simply the sequence of\u00a0<\/span>amino acid<\/span>s that make up the\u00a0<\/span>polypeptide chain<\/span>.\u00a0<\/span>\r\n\r\nThe interactions of the functional groups and R groups of the amino acids form hydrogen, ionic, and disulfide bonds, along with polar\/nonpolar interactions. These interactions lead to the formation of secondary, tertiary, and quaternary protein structures. <\/span>\r\n\r\nThese groups are composed primarily of carbon, hydrogen, oxygen, nitrogen, and sulfur, in the form of hydrocarbons, acids, amides, alcohols, and amines.<\/span>\r\n

The secondary structure : <\/strong>When the chain is sufficiently long, hydrogen bonding may occur between amine and carbonyl functional groups within the peptide backbone (excluding the\u00a0<\/span>R<\/em>\u00a0<\/span>side group),<\/p>\r\nThis results in localized folding of the polypeptide chain into helices and sheets.\r\n\r\nThese shapes constitute a protein\u2019s\u00a0<\/span>secondary structure<\/span>. The most common secondary structures are the \u03b1-helix and \u03b2-pleated sheet.\r\n\r\nIn the\u00a0\u03b1-helix<\/span>\u00a0structure,<\/strong> the helix is held by hydrogen bonds between the oxygen atom in a\u00a0<\/span>carbonyl group<\/span>\u00a0<\/span>of one amino acid and the hydrogen atom of the amino group that is just four amino acid units farther along the chain.\r\n\r\nIn the\u00a0<\/span>\u03b2-pleated sheet<\/span>,<\/strong> the pleats are formed by similar\u00a0<\/span>hydrogen bonds<\/span>\u00a0<\/span>between continuous sequences of carbonyl and\u00a0<\/span>amino groups<\/span>\u00a0<\/span>that are further separated on the backbone of the polypeptide chain\r\n

The tertiary structure : <\/span><\/strong>\u00a0This is the\u00a0 three-dimensional shape of a single polypeptide chain.<\/p>\r\nTertiary structure is determined by interactions between amino acid residues that are far apart in the chain.\r\n\r\nA variety of interactions give rise to protein tertiary structure, such as\u00a0<\/span>disulfide bridge<\/span>s, which are bonds between the sulfhydryl (\u2013SH) functional groups on amino acid side groups; hydrogen bonds; ionic bonds; and hydrophobic interactions between nonpolar side chains.\r\n\r\nAll of these interactions, weak and strong, combine to determine the final three-dimensional shape of the protein and its function\r\n\r\nAs the result polypeptide chain assumes a large-scale, three-dimensional shape is called\u00a0<\/span>protein folding<\/span>.\r\n\r\nFolded proteins that are fully functional in their normal biological role are said to possess a\u00a0<\/span>native structure<\/span>.\r\n\r\nWhen a protein loses its three-dimensional shape, it may no longer be functional. These\u00a0<\/span>unfolded proteins<\/span>\u00a0<\/span>are\u00a0<\/span>denatured<\/span>.\r\n\r\nDenaturation implies the loss of the\u00a0<\/span>secondary structure<\/span>\u00a0<\/span>and\u00a0<\/span>tertiary structure<\/span> and, the<\/span>\u00a0quaternary structure) without the loss of the primary structure.\r\n

The Quarternary structure\u00a0 :<\/strong> Some proteins are assemblies of several separate\u00a0<\/span>polypeptide<\/span>s, also known as\u00a0<\/span>protein subunit<\/span>s. The interactions that hold these subunits together constitute the\u00a0<\/span>quaternary structure<\/span>\u00a0<\/span>of the protein.<\/p>\r\nThe overall quaternary structure is stabilized by relatively weak interactions. Hemoglobin, for example, has a quaternary structure of four globular protein subunits: two \u03b1 and two \u03b2 polypeptides, each one containing an iron-based heme .\r\n

Another important class of proteins is the\u00a0<\/span>conjugated proteins<\/span>\u00a0<\/span>that have a nonprotein portion. If the conjugated protein has a carbohydrate attached, it is called a\u00a0<\/span>glycoprotein<\/span>. If it has a lipid attached, it is called a\u00a0<\/span>lipoprotein<\/span>.<\/p>\r\n\"The\r\n

\"Primary structure of protein\"<\/a>\u00a0by\u00a0<\/span>Openstax<\/a><\/a><\/a>\u00a0is licensed under\u00a0<\/span>CC BY 4.0<\/a><\/p>\r\n\"The\r\n

\"Secondary structure of protein\"<\/a>\u00a0by\u00a0<\/span>Openstax<\/a><\/a><\/a>\u00a0is licensed under\u00a0<\/span>CC BY 4.0<\/a><\/p>\r\n \r\n\r\n\"A\r\n

\"Tertiary structure of protein\"<\/a>\u00a0by\u00a0<\/span>Openstax<\/a><\/a><\/a>\u00a0is licensed under\u00a0<\/span>CC BY 4.0<\/a><\/p>\r\n \r\n\r\n \r\n\r\n\"A\r\n

\"Quaternary structure of protein\"<\/a>\u00a0by\u00a0<\/span>Openstax<\/a><\/a><\/a>\u00a0is licensed under\u00a0<\/span>CC BY 4.0<\/a><\/p>\r\n \r\n

Test your understanding about macromolecules of the cell\u00a0<\/span><\/h2>\r\n[h5p id=\"37\"]<\/span>\r\n\r\n ","rendered":"

The next abundant constituent of cell is\u00a0 Proteins. They perform numerous functions vital to all organisms. <\/span><\/p>\n

These are made from amino acids <\/span><\/p>\n

They function as structural components of cells and subcellular entities.<\/span><\/p>\n

They act as sources of nutrients, as atom- and energy-storage reservoirs, and <\/span><\/p>\n

They are functional species such as hormones, enzymes, receptors, and transport molecules.<\/span><\/p>\n

Aminoacids<\/h1>\n

These are organic molecules .<\/p>\n

They contain a\u00a0hydrogen atom, a\u00a0<\/span>carboxyl group<\/span>\u00a0(\u2013COOH), and an amino group (\u2013NH<\/span>2<\/sub>) and all of these are bonded to the same carbon atom, called\u00a0<\/span>\u03b1 carbon<\/span>. <\/span><\/p>\n

The fourth group bonded to the \u03b1 carbon varies among the different amino acids and is called a\u00a0<\/span>residue<\/span>\u00a0or a\u00a0<\/span>side chain<\/span>, represented in structural formulas by the letter\u00a0<\/span>R<\/em>. <\/span><\/p>\n

When two or more amino acids combine, water molecule is removed and the two amino acids are connected by a covalent bond called the Peptide bond, <\/a> <\/strong>which is formed by the <\/span>reaction of the\u00a0<\/span>carboxylic acid<\/span> group of one amino acid molecule with the\u00a0<\/span>amine group<\/span> of another amino acid molecule. The resulting molecule is called a Peptide.<\/strong><\/span><\/p>\n

\u00a0Prefixes are often used to specify these numbers of amino acids that join for example dipeptides<\/span>\u00a0(two amino acids),\u00a0<\/span>tripeptide<\/span>s (three amino acids) etc., <\/span><\/p>\n

In general <\/span>oligopeptide<\/span>s<\/strong>\u00a0are formed by joining up to approximately 20 amino acids, whereas\u00a0<\/span>polypeptide<\/span>s<\/strong>\u00a0are synthesized from up to approximately 50 amino acids.<\/span><\/p>\n

\"Alanine<\/p>\n

“Proteins”<\/a>\u00a0by\u00a0<\/span>OpenStax<\/a><\/a><\/a>\u00a0is licensed under\u00a0<\/span>CC BY 4.0<\/a><\/p>\n

When the number of amino acids linked together becomes very large, or when multiple polypeptides are used as building subunits, the macromolecules that result are called\u00a0<\/strong><\/span>proteins<\/span>.<\/strong><\/p>\n

Protein Structure<\/h2>\n

The size (length) and specific amino acid sequence of a protein are major determinants of its shape, and the shape of a protein is critical to its function.<\/span><\/p>\n

Protein structure is categorized in terms of four levels: primary, secondary, tertiary, and quaternary.<\/span><\/p>\n

The\u00a0primary structure :<\/span><\/strong>\u00a0<\/strong>is simply the sequence of\u00a0<\/span>amino acid<\/span>s that make up the\u00a0<\/span>polypeptide chain<\/span>.\u00a0<\/span><\/p>\n

The interactions of the functional groups and R groups of the amino acids form hydrogen, ionic, and disulfide bonds, along with polar\/nonpolar interactions. These interactions lead to the formation of secondary, tertiary, and quaternary protein structures. <\/span><\/p>\n

These groups are composed primarily of carbon, hydrogen, oxygen, nitrogen, and sulfur, in the form of hydrocarbons, acids, amides, alcohols, and amines.<\/span><\/p>\n

The secondary structure : <\/strong>When the chain is sufficiently long, hydrogen bonding may occur between amine and carbonyl functional groups within the peptide backbone (excluding the\u00a0<\/span>R<\/em>\u00a0<\/span>side group),<\/p>\n

This results in localized folding of the polypeptide chain into helices and sheets.<\/p>\n

These shapes constitute a protein\u2019s\u00a0<\/span>secondary structure<\/span>. The most common secondary structures are the \u03b1-helix and \u03b2-pleated sheet.<\/p>\n

In the\u00a0\u03b1-helix<\/span>\u00a0structure,<\/strong> the helix is held by hydrogen bonds between the oxygen atom in a\u00a0<\/span>carbonyl group<\/span>\u00a0<\/span>of one amino acid and the hydrogen atom of the amino group that is just four amino acid units farther along the chain.<\/p>\n

In the\u00a0<\/span>\u03b2-pleated sheet<\/span>,<\/strong> the pleats are formed by similar\u00a0<\/span>hydrogen bonds<\/span>\u00a0<\/span>between continuous sequences of carbonyl and\u00a0<\/span>amino groups<\/span>\u00a0<\/span>that are further separated on the backbone of the polypeptide chain<\/p>\n

The tertiary structure : <\/span><\/strong>\u00a0This is the\u00a0 three-dimensional shape of a single polypeptide chain.<\/p>\n

Tertiary structure is determined by interactions between amino acid residues that are far apart in the chain.<\/p>\n

A variety of interactions give rise to protein tertiary structure, such as\u00a0<\/span>disulfide bridge<\/span>s, which are bonds between the sulfhydryl (\u2013SH) functional groups on amino acid side groups; hydrogen bonds; ionic bonds; and hydrophobic interactions between nonpolar side chains.<\/p>\n

All of these interactions, weak and strong, combine to determine the final three-dimensional shape of the protein and its function<\/p>\n

As the result polypeptide chain assumes a large-scale, three-dimensional shape is called\u00a0<\/span>protein folding<\/span>.<\/p>\n

Folded proteins that are fully functional in their normal biological role are said to possess a\u00a0<\/span>native structure<\/span>.<\/p>\n

When a protein loses its three-dimensional shape, it may no longer be functional. These\u00a0<\/span>unfolded proteins<\/span>\u00a0<\/span>are\u00a0<\/span>denatured<\/span>.<\/p>\n

Denaturation implies the loss of the\u00a0<\/span>secondary structure<\/span>\u00a0<\/span>and\u00a0<\/span>tertiary structure<\/span> and, the<\/span>\u00a0quaternary structure) without the loss of the primary structure.<\/p>\n

The Quarternary structure\u00a0 :<\/strong> Some proteins are assemblies of several separate\u00a0<\/span>polypeptide<\/span>s, also known as\u00a0<\/span>protein subunit<\/span>s. The interactions that hold these subunits together constitute the\u00a0<\/span>quaternary structure<\/span>\u00a0<\/span>of the protein.<\/p>\n

The overall quaternary structure is stabilized by relatively weak interactions. Hemoglobin, for example, has a quaternary structure of four globular protein subunits: two \u03b1 and two \u03b2 polypeptides, each one containing an iron-based heme .<\/p>\n

Another important class of proteins is the\u00a0<\/span>conjugated proteins<\/span>\u00a0<\/span>that have a nonprotein portion. If the conjugated protein has a carbohydrate attached, it is called a\u00a0<\/span>glycoprotein<\/span>. If it has a lipid attached, it is called a\u00a0<\/span>lipoprotein<\/span>.<\/p>\n

\"The<\/p>\n

“Primary structure of protein”<\/a>\u00a0by\u00a0<\/span>Openstax<\/a><\/a><\/a>\u00a0is licensed under\u00a0<\/span>CC BY 4.0<\/a><\/p>\n

\"The<\/p>\n

“Secondary structure of protein”<\/a>\u00a0by\u00a0<\/span>Openstax<\/a><\/a><\/a>\u00a0is licensed under\u00a0<\/span>CC BY 4.0<\/a><\/p>\n

 <\/p>\n

\"A<\/p>\n

“Tertiary structure of protein”<\/a>\u00a0by\u00a0<\/span>Openstax<\/a><\/a><\/a>\u00a0is licensed under\u00a0<\/span>CC BY 4.0<\/a><\/p>\n

 <\/p>\n

 <\/p>\n

\"A<\/p>\n

“Quaternary structure of protein”<\/a>\u00a0by\u00a0<\/span>Openstax<\/a><\/a><\/a>\u00a0is licensed under\u00a0<\/span>CC BY 4.0<\/a><\/p>\n

 <\/p>\n

Test your understanding about macromolecules of the cell\u00a0<\/span><\/h2>\n

<\/p>\n

\n