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Chemical Composition of Biomass
Published in Jean-Luc Wertz, Philippe Mengal, Serge Perez, Biomass in the Bioeconomy, 2023
Jean-Luc Wertz, Philippe Mengal, Serge Perez
Their principal structural elements are polypeptide chains, although they may be combined with fats as lipoproteins and with polysaccharides as glycoproteins. Proteins have complex structures based on their amino acid composition (primary structure), three-dimensional substructures including helices and beta sheets (secondary structure), the way subunits are linked together to form a polypeptide chain (tertiary structure), and how the different polypeptide chains may be packed together to form the overall structure of the protein (quaternary structure). Molecular weights vary from thousands to millions Dalton. The molecules may consist of one single chain, or two or more chains joined together. Globular proteins consist of chains tightly intertwined to form a nearly spherical shape. In some more complex proteins, these spherical units may themselves be joined together by non-covalent forces into larger structures of the fairly precise form (Figure 5.16).
Petroleum Geochemical Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
Proteins are of two types; one is fibrous and the other is globular. Fibrous proteins support and connect the tissues, muscles, skin and hair of the body. Fibrous proteins are comparatively stable and non-reactive. Globular proteins maintain and regulate the biological functions in living organisms. Another class of proteins contains a non-protein group as well in their molecular structure. The non-protein groups can be either carbohydrate (glucose) or lipid or nucleic acid or a metal ion. Accordingly proteins are named as carbohydrate-protein, lipo-protein, nucleo-protein and metallic-protein. Non-protein groups impart additional biological functions in the protein. Some proteins also act as catalysts. Such a protein is known as a catalytic enzyme. It catalyzes certain biological metabolism processes. Enzymes are more active and flexible than proteins.
Proteins in Solution and at Interfaces
Published in E. D. Goddard, K. P. Ananthapadmanabhan, Interactions of Surfactants with Polymers and Proteins, 2018
Proteins are the complex unbranched polymers that play a crucial role in the structure and function of biological cells and organisms. The individual L-α-amino acids are linked together head-to-tail by peptide bonds to form linear chains containing up to several hundred monomer units (residues). Protein molecular weights are typically in the range from 104 to 105 Da. Structures vary enormously depending on the sequence of amino acid residues, but they may be roughly classified into three main types: fibrous, globular, and disordered. Fibrous proteins are composed of polypeptide chains arranged to lie along a common linear axis. The functionality of fibrous proteins (collagen, keratin, etc.) is largely associated with their structural and mechanical properties in tissues such as bone, muscle, skin, and hair. In a globular protein, one or more polypeptide chains are folded compactly and uniquely together to form a three-dimensional structure with a roughly spherical shape and a complicated surface topology. Most globular proteins function as enzymes (trypsin, catalase, etc.), but some have other biological functions — as hormones (insulin), in transfer processes (hemoglobin), as a food supply (ovalbumin), and so on. Most fibrous and globular proteins become more disordered on heating. A few proteins have so little ordered structure in the native state that it is convenient to call them disordered. Notable examples are the milk proteins αs1-casein and β-casein.
Volumetric and viscometric properties of amino acids in aqueous solutions of various drugs at different temperatures: A review
Published in Molecular Physics, 2022
Ruby Rani, Shikha Rajput, Keshav Sharma, Vikrant Baboria
Globular proteins form a class of macromolecules which have well defined physicochemical properties and functions in biological systems. They have a marginally stable native structure that results from a fine balance among various non-covalent forces: ionic and dipolar interactions, hydrogen bonding, hydrophobic forces, etc [1,2]. The process of denaturation of a globular protein in aqueous solutions involves a change from the native state, in which the protein adopts its characteristic folded conformation, to the denaturated state where the protein is predominantly in an extended form [3,4]. Upon unfolding, the interactions between protein groups within the core are disrupted and replaced with the interactions of these groups with the solvent, thus leading to change in protein solvation. The study of these protein solvent interactions is difficult because of the complexity of the interactions in such a large molecule. However, one useful approach, which can be helpful in understanding these interactions, is to study simple compounds such as amino acids, which model some specific aspects of the protein structure. The interactions between solvent and various constituent groups of proteins such as amino acid side chain and the peptide backbone group play a central role in the structure, the conformation and the function of proteins in aqueous solutions [5,6].