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Proteins and proteomics
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2018
Translation proceeds in four phases—activation, initiation, elongation, and termination—and all describe the growth of the amino acid chain or polypeptide, which is the product of translation. Amino acids are brought to ribosomes and assembled into proteins. In activation, the correct amino acid is covalently bonded to the correct tRNA. While this is not technically a step in translation, it is required for translation to proceed. The amino acid is joined by its carboxyl group to the 3′ OH of the tRNA by an ester bond. When the tRNA has an amino acid linked to it, it is termed “charged.” Initiation involves the small subunit of the ribosome binding to the 5′ end of mRNA with the help of initiation factors (IFs). Termination of the polypeptide happens when the A site of the ribosome faces a stop codon (UAA, UAG, or UGA). When this happens, no tRNA can recognize it, but a releasing factor can recognize nonsense codons and causes the release of the polypeptide chain. The 5′ end of the mRNA gives rise to the protein’s N-terminus, and the direction of translation can, therefore, be stated as N → C. A number of antibiotics act by inhibiting translation. Some of these are anisomycin, cycloheximide, chloramphenicol, tetracycline, streptomycin, erythromycin, and puromycin. Prokaryotic ribosomes have a different structure from that of eukaryotic ribosomes, and thus antibiotics can specifically target bacterial infections without any detriment to a eukaryotic host’s cells. The mRNA carries genetic information encoded as a ribonucleotide sequence from the chromosomes to the ribosomes. The ribonucleotides are “read” by translational machinery in a sequence of nucleotide triplets called codons. Each of those triplets codes for a specific amino acid. The ribosome and tRNA molecules translate this code to a specific sequence of amino acids. The ribosome is a multisubunit structure containing rRNA and proteins. It is the “factory” where amino acids are assembled into proteins. tRNAs are small noncoding RNA chains (74–93 nucleotides) that transport amino acids to the ribosome. tRNAs have a site for amino acid attachment called an anticodon. The anticodon is an RNA triplet complementary to the mRNA triplet that codes for their cargo amino acid.
Proteins and Proteomics
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2020
Translation proceeds in four phases: activation, initiation, elongation, and termination, and all describe the growth of the amino acid chain or polypeptide that is the product of translation. Amino acids are brought to ribosomes and assembled into proteins. In activation, the correct amino acid is covalently bonded to the correct tRNA. Although this is not technically a step in translation, it is required for translation to proceed. The amino acid is joined by its carboxyl group to the 3′ OH of the tRNA via an ester bond. When the tRNA has an amino acid linked to it, it is considered “charged.” Initiation involves the small subunit of the ribosome binding to the 5′ end of mRNA with the help of initiation factors (IFs). Termination of the polypeptide happens when the A site of the ribosome faces a stop codon (UAA, UAG, or UGA). When this happens no tRNA can recognize it, but a releasing factor can recognize nonsense codons and causes the release of the polypeptide chain. The 5′ end of the mRNA gives rise to the protein’s N-terminus, and the direction of translation can therefore be stated as N → C. A number of antibiotics act by inhibiting translation. Some of these are anisomycin, cycloheximide, chloramphenicol, tetracycline, streptomycin, erythromycin, and puromycin. Prokaryotic ribosomes have a different structure from that of eukaryotic ribosomes, and thus antibiotics can specifically target bacterial infections without any detriment to a eukaryotic host’s cells. The mRNA carries genetic information encoded as a ribonucleotide sequence from the chromosomes to the ribosomes. The ribonucleotides are “read” by translational machinery in a sequence of nucleotide triplets called codons. Each of these triplets codes for a specific amino acid. The ribosome and tRNA molecules translate this code to a specific sequence of amino acids. The ribosome is a multisubunit structure containing rRNA and proteins. It is the “factory” where amino acids are assembled into proteins. tRNAs are small noncoding RNA chains (74–93 nucleotides) that transport amino acids to the ribosome. tRNAs have a site for amino acid attachment called an anticodon. The anticodon is a tRNA triplet complementary to the mRNA triplet that codes for their cargo amino acid.
Benefits of β-hydroxy-β-methylbutyrate supplementation in trained and untrained individuals
Published in Research in Sports Medicine, 2019
Yftach Gepner, Alyssa N. Varanoske, David Boffey, Jay R. Hoffman
The mechanism responsible for HMB’s role as an ergogenic aid appears to be related to its effect on stimulating muscle protein synthesis and attenuating muscle protein degradation. HMB has been demonstrated to enhance muscle protein synthesis by increasing phosphorylation of mammalian target of rapamycin (mTOR) and its downstream targets; ribosomal protein S6 kinase (S6K) and eukaryotic initiation factor-4 binding protein-1 (4EBP1) (Aversa et al., 2011; Eley et al., 2007). Others though have also suggested that HMB may have direct action on the proliferation and differentiation of myoblasts through stimulating satellite cell activation in skeletal muscle (Kornasio et al., 2009). HMB is also thought to attenuate protein degradation by inhibiting the ubiquitin-proteasome–mediated proteolytic pathway leading to muscle degradation through several mechanisms (Smith, Mukerji, & Tisdale, 2005). HMB has been reported to regulate Forkhead box O (FoxO) proteins that are responsible for protein degradation and apoptosis (Kimura et al., 2014; Park et al., 2013). In addition, HMB has been shown to attenuate the mechanisms inhibiting the elongation phase of translation during protein metabolism (Eley, Russell, & Tisdale, 2008a), attenuate proteolysis inducing factor (Eley et al., 2007) and inhibit caspase activity (Eley, Russell, & Tisdale, 2008b).
Carnosine in health and disease
Published in European Journal of Sport Science, 2019
Guilherme Giannini Artioli, Craig Sale, Rebecca Louise Jones
Ageing is a multifactorial process, resulting from several persistent deleterious effects that negatively alter cellular and organism homeostasis. McFarland and Holliday (1994, 1999) suggested that carnosine could act as an anti-ageing agent, with improvements to the Hayflick limit (the maximum number of times cells can divide), and the apparent rejuvenation of senescent cells. Numerous possible anti-ageing outcomes of carnosine have been proposed, including effects on reactive species (Kohen, Yamamoto, Cundy, & Ames, 1988), inhibitory effects on glycolysis in tumour cells (Iovine et al., 2012), stimulatory effects on mitochondrial activity (Renner, Asperger, et al., 2010), reduced toxic metabolite and methylglyoxal formation (Hipkiss, Michaelis, & Syrris, 1995), reduction of translation initiation factor phosphorylation, slowing translation, thus reducing error-protein generation (Son, Satsu, Kiso, Totsuka, & Shimizu, 2008), and slowed telomere shortening (Shao, Li, & Tan, 2004). Although these findings are promising, current evidence is mostly limited to in vitro and cultured cell models, with little being known about the physiological relevance of these properties. It also remains unclear exactly how carnosine can affect cellular lifespan and the onset of age-related changes in tissue function.
Neurotoxicity and physiological stress in brain of zebrafish chronically exposed to tributyltin
Published in Journal of Toxicology and Environmental Health, Part A, 2021
The endoplasmic reticulum (ER) is the intracellular organelle responsible for various aspects of the quality control of biologically active proteins, such as synthesis, folding, posttranslational modification, and delivery (Zhao et al. 2014). It has been well documented that there are three known molecular sensors on the endoplasmic reticulum, namely ire1, atf6 and perk, which sense and transmit UPR signals (Cheng, Chen, and Chen 2017; Jia et al. 2019). When ER is under physiological stress, the related pathways might be activated including the protein kinase RNA-activated-like ER kinase (PERK)–eukaryotic translation initiation factor 2 alpha (eIF2α) pathway, the inositol requiring enzyme 1 (IRE1)–X-box binding protein 1 (XBP1) pathway. In agreement with Komoike and Matsuoka (2013) the expression levels of atf6, perk, ire1 and xbp1s were all up-regulated in our study, which indicated that exposure of zebrafish to TBT induced a ERS response via activation of both the PERK–eIF2α and IRE1–XBP1 pathways. Further, the up-regulation of transcription levels of apoptosis-related genes, bax, caspase-3, caspase-8 and caspase-9, suggested that the ERS-mediated apoptotic pathways are involved in the process of TBT-induced brain injury. The Nrf2 pathway plays a key function in regulating cellular oxidative stress (Tong et al. 2006). When cells are stimulated by external stimuli, Nrf2 is activated and then enters the nucleus to activate downstream antioxidant genes, including quinone dehydrogenase 1 (NQO1), glutamic acid cysteine ligase modified subunit (GCLM) and GCLC, leading to stress response in the body (Jin et al. 2017). In our study, TBT resulted in significantly increased mRNA levels of nrf2, nqo1 and gclc, which is consistent with the oxidation reaction noted through elevated MDA levels.