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Separation and Purification in Biotechnology
Published in Shintaro Furusaki, John Garside, L.S. Fan, The Expanding World of Chemical Engineering, 2019
Proteins and polypeptides are the most important of the various biochemical products. A scheme for the synthesis of proteins in vivo is shown in Figure 14.2. A gene encoding a protein in DNA is transcribed to mRNA by RNA polymerase. Then, according to the information about the amino acid sequence (the primary structure) written in mRNA the protein is synthesized. The characteristics of the amino acid sequence determine partial conformations such as a-helices and (sheets (the secondary structure) and a specific steric structure of the protein (the tertiary structure). Sometimes several subunits aggregate to form an oligomeric protein (the quaternary structure). The specific biological activity of the protein depends on the steric structure. Since tens or even hundreds of the twenty kinds of amino acids make peptide bonds to construct protein molecules, an enormous variety of proteins with different characteristics can exist.
Reactivity and Bio Samples Probed by Tip-Enhanced Raman Spectroscopy
Published in Marc Lamy de la Chapelle, Nordin Felidj, Plasmonics in Chemistry and Biology, 2019
Zhenglong Zhang, Robert Meyer, Volker Deckert
Considering proteins, it is noteworthy to mention their structures, because they can give access about mechanisms contributing to several cellular processes. As mentioned above, a long polypeptide chain forms a protein. Its primary structure describes simply the amino acid sequences. The secondary structure gives access to the composition and the spatial arrangement of the protein. A distinction is made in α-helix, β-sheet, β-turn, and β-helix. The first two- and most common structures, revealing a distance of only a few Ångströms between the amino acids in β-sheet and α-helix conformation, subsequently involving a starting point for TERS and its métier to differentiate the chemical composition onto this small scale. Furthermore, the tertiary structure describes the general shape of a single protein molecule, as the quaternary structure is formed by several proteins that have to merge in order to stay functional.
Biocatalysis: An introduction
Published in Grunwald Peter, Biocatalysis and Nanotechnology, 2017
The next structural level of proteins is characterized by secondary structure elements, mainly the a-helix and the b-sheet. Their formation occurs spontaneously through the interaction between neighbored amino acid residues. These non-covalent interactions are stabilized by hydrogen bonds (binding energy ~40 kJ/mol) and fold into domains to yield a characteristic 3D or tertiary structure, maintained by forces acting between charged and/or hydrophobic amino acid residues, and dipole-dipole interactions. Different domains within a protein may be linked by oligopeptide loops. Another aspect contributing significantly to the stability of the protein molecule is the hydrophobic effect; it results from the fact that folding in an aqueous surrounding leads to a more or less water-free hydrophobic core whereas polar and charged amino acid residues are preferentially located on the protein surface. Finally, a variety of enzymes form a quaternary structure through the non-covalent interaction of subunits. The correct folding of proteins is assisted by ATP-dependent folding catalysts known as chaperones. They play, e.g., an important role in the endoplasmic reticulum and its associated degradation machinery in connection with the synthesis of glycoproteins (e.g., Ninagawa et al., 2014; Lederkremer, 2007).
Lead induces DNA damage and alteration of ALAD and antioxidant genes mRNA expression in construction site workers
Published in Archives of Environmental & Occupational Health, 2019
Zertashia Akram, Sadaf Riaz, Mahmood Akhtar Kayani, Sarwat Jahan, Malik Waqar Ahmad, Muhammad Abaid Ullah, Hizbullah Wazir, Ishrat Mahjabeen
Additionally, lead inhibits three enzymes in the heme biosynthesis pathway: delta-aminolevulinic acid dehydratase (ALAD), coporphyrinogen oxidase, and ferrochelatase. But its effects on ALAD are the most profound.14 Exposure to lead may also result in significant adverse health effects to hepatic and renal systems.15–17 Lead strongly inhibits ALAD enzyme stoichiometrically, changes the enzyme's quaternary structure, and initiated the lead-induced toxicity in brain, renal region, and in reproductive organs.18,19 Many earlier studies have reported the association of ALAD polymorphisms with lead-induced toxicity in different body organs, such as hepatic region, renal region, brain region, and different reproductive organs.20–22 To date, no study is available for expression variations of ALAD gene in lead-exposed individuals in Pakistani population.