China
Africa
Explore chapters and articles related to this topic
Bacteria
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
DNA carries the genetic information to determine heritable properties of an organism (i.e., its phenotype). The DNA is initially transcribed into complementary polymers of ribonucleic acid (RNA) in the form called messenger RNA (mRNA). The mRNA subsequently serves as a template for synthesis of protein molecules; a process that is mediated by ribosomes. Ribosomes are microparticles composed of protein linked to another class of RNA called ribosomal RNA (rRNA). Ribosomes consist of smaller (30S) and larger (50S) subunits and tend to form aggregates or strands called polyribosomes.
Morphology of Mononuclear and Malignant Cells
Published in Richard C. Niemtzow, Transmembrane Potentials and Characteristics of Immune and Tumor Cell, 2020
In transmission EM preparations, the monocyte has an indented horseshoe-shaped nucleus with clumped chromatin predominant near the nuclear membrane. Usually there is one nucleolus present. The monocyte has a full complement of cytoplasmic organelles including a well-developed Golgi complex. Mitochondria are present as well as primary lysosomes and almost always secondary lysosomes — either phagosomes or autosomes — containing phagocytized material. Depending on the state of activity, various amounts of membrane- bound polyribosomes are present as rough-surfaced endoplasmic reticulum or RER. For synthesis of protein to be used outside the cell or nonmembrane-bound polyribosomes for the synthesis of proteins to be used inside the cell. Also, pseudopodia in varying numbers and microtubular elements can be seen.15
Interactions of Growth Factors, Hormones, and Oncogenes Controlling the Proliferation of Normal and Cancer Cells
Published in Velibor Krsmanović, James F. Whitfield, Malignant Cell Secretion, 2019
James F. Whitfield, Jon P. Durkin
Growth factor deprivation signals the immortalized cells of established lines to stop growing and cycling by affecting all aspects of RNA and protein metabolism (for a review see Reference 109). The cell reduces transcription and/or destabilizes the transcripts of cell cycle genes or proto-oncogenes, decreases synthesis and increases degradation of ribosomal RNA, and increases degradation and decreases the translocation to the nucleus of short-lived nonhistone proteins that regulate chromatin structure.109,216,291-295 However, the quiescent cells do continue to express the genes for, but do not produce, histones, and the DNA replication enzymes dCMP kinase, dihydrofolate reductase, DNA polymerase a, NDP kinase, thymidine kinase, and thymidylate synthase.296-299 Some cells even continue to maintain a pool of CDC2(Hs) protein which is the principal component of the MPFs that trigger mitotic prophase.300 On the other hand, they start expressing the genes for factors which keep them in the quiescent state.301-305 In general, only the mRNA needed for minimal housekeeping and the quiescence factors are translated, while the number of polyribosomes drops as the cell shunts a large fraction of its mRNA into a rapidly mobilizable nonpolysomal pool.109,295,306-308
Exploring the rationale for thermotherapy in COVID-19
Published in International Journal of Hyperthermia, 2021
Javier Mancilla-Galindo, Norma Galindo-Sevilla
Cells are adapted to perform their functions most efficiently at a specific temperature. For instance, testicles in mice and humans are exposed to lower temperatures than core body temperature (i.e., 34 °C vs 37 °C). After exposure of mice spermatids to 34 °C, 37 °C, and 40 °C for 1 h, protein synthesis decreased in approximately 25% at 37 °C and 50% at 40 °C when compared to 34 °C [24]. RNA templates called messenger RNA (mRNA) are normally used by cell ribosomes to assemble amino acids into proteins, ribosomes can group into polyribosomes to enhance protein synthesis. In the study by Nakamura and Hall, temperature-dependent reductions in polyribosomes were associated to decreased protein synthesis. HeLa cells exposed to 42 °C also had disaggregation of polyribosomes leading to lower protein synthesis [25].
Platelets as a surrogate disease model of neurodevelopmental disorders: Insights from Fragile X Syndrome
Published in Platelets, 2018
David Pellerin, Audrey Lortie, François Corbin
Although FMRP is transferred from megakaryocytes to platelets as part of mRNP complexes [30], the protein has been surprisingly shown to be completely dissociated from polyribosomes in circulating quiescent platelets [31]. This finding markedly contrasts with all previous reports showing a strong association of FMRP with polyribosomes in other cell types [33,34,134,137]. Similarly, the FMRP homologs FXR1 and FXR2, usually associated with the 60S ribosomal subunit [138], were also found to be dissociated from ribosomes in blood platelets [31]. These results are, however, consistent with the near-absent resting translation in quiescent platelets [136,139]. In fact, platelets are terminally differentiated cells with a unique and very specific physiological function whose proteome is almost completely acquired from megakaryocytes during thrombopoiesis. Accordingly, newly formed platelets exiting the bone marrow already carry the majority of proteins needed for initiation of aggregation and therefore do not require active translation while quiescent. On the other hand, platelet activation induces, through the PI3K/Akt/mTOR pathway, rapid and sustained translation of some proteins essential to the hemostatic process and cytoskeletal contraction [136,139]. It is yet unknown if FMRP binds to polyribosomes upon platelet activation and if the protein has any function at all in quiescent platelets given its unusual distribution. Its dissociation from polyribosomes is in complete disagreement with its elementary RNA-binding function as suggested by its structure [140,141]. Nonetheless, this subcellular localization does not exclude that FMRP somewhat plays a role in mRNA stabilization and metabolism within platelets. The study of blood platelets might therefore uncover unexpected functions of FMRP.
Mining for missed sORF-encoded peptides
Published in Expert Review of Proteomics, 2019
Xinqiang Yin, Yuanyuan Jing, Hanmei Xu
Polysome profiling is another technique that captures mRNA protected by polyribosomes and subsequently sequences the obtained RNA fractions. Polysomal fragments are separated following a classic sucrose gradient and fragments containing 2–6 ribosomes is profiled [87]. This method ensures that the ribosome-bound fragments (RBFs) detected arise from genuine translation events. But the polysome profiling strategy is not suitable for identifying sORF less than 30 codons for its low resolution.