Your browser does not fully support modern features. Please upgrade for a smoother experience.
Subject:
All Disciplines Arts & Humanities Biology & Life Sciences Business & Economics Chemistry & Materials Science Computer Science & Mathematics Engineering Environmental & Earth Sciences Medicine & Pharmacology Physical Sciences Public Health & Healthcare Social Sciences
Sort by:
Most Viewed Latest Alphabetical (A-Z) Alphabetical (Z-A)
Filter:
All Topic Review Biography Peer Reviewed Entry Video Entry
Topic Review
Post-Transcriptional Regulation
Post-transcriptional regulation comprises the molecular processes that control the maturation, molecular fate, abundance, localization, and functional output of RNA molecules after their synthesis. In protein-coding gene expression, it encompasses RNA processing events—including 5′-end capping, splicing, editing, and 3′-end cleavage and polyadenylation—as well as nuclear export, subcellular localization, translational control, RNA surveillance, and degradation. These regulatory activities operate through cis-acting RNA sequence and structural elements, RNA chemical modifications, and trans-acting factors such as RNA-binding proteins, regulatory non-coding RNAs, RNA-processing enzymes, and ribonucleoprotein complexes [1][2][3]. By determining which RNA isoforms persist, where they accumulate, how long they remain available, and the extent to which they are translated, post-transcriptional regulation establishes RNA-specific and context-dependent patterns of gene expression [1][2].
  • 5
  • 23 Sep 2026
Topic Review
Glycoprotein
A glycoprotein is a protein molecule bearing one or more covalently attached carbohydrate chains, termed glycans. The protein component provides the polypeptide scaffold, while the glycan component consists of monosaccharide residues joined through specific glycosidic linkages and assembled at defined amino-acid sites or within particular protein regions. Protein glycosylation generates major classes of glycoproteins through N-linked glycans attached to asparagine residues, O-linked glycans attached to hydroxyl-containing amino acids such as serine or threonine, and additional linkage types including C-mannosylation and glycosylphosphatidylinositol-associated protein modification [1][2]. Glycan assembly is mediated by glycosyltransferases and glycosidases and occurs through compartmentalized biosynthetic pathways, especially in the endoplasmic reticulum and Golgi apparatus of eukaryotic cells [2][3]. A glycoprotein population may contain multiple glycoforms because glycan occupancy, monosaccharide composition, linkage, branching, and terminal modifications can vary among molecules bearing the same polypeptide sequence [1][4].
  • 5
  • 24 Sep 2026
Topic Review
Enzyme Activity
Enzyme activity is the measurable rate at which an enzyme catalyzes the conversion of substrate molecules into reaction products under specified experimental or cellular conditions. It represents the amount of chemical transformation occurring per unit time and depends on the concentration of catalytically competent enzyme, substrate availability, temperature, pH, ionic composition, cofactors, and the concentrations of products and regulatory molecules [1][2]. In kinetic analysis, activity is commonly quantified as an initial reaction velocity, determined while substrate depletion and product accumulation remain limited. For enzymes following a steady-state single-substrate mechanism, the relationship between initial velocity and substrate concentration is described by the Michaelis–Menten equation, whose parameters include the maximal velocity (V<sub>max</sub>) and the Michaelis constant (K<sub>M</sub>) [1][3]. Catalytic turnover is expressed by k<sub>cat</sub>, the number of substrate molecules converted per active site per unit time under saturating substrate conditions [2]. Enzyme activity also encompasses changes in catalytic rate produced by reversible inhibitors, irreversible inactivators, allosteric effectors, covalent modification, and substrate or product binding [2][4].
  • 5
  • 24 Sep 2026
Topic Review
RNA Transcription
RNA transcription is the template-directed enzymatic synthesis of an RNA molecule from a defined DNA sequence. It is catalyzed by RNA polymerase, which locally separates the DNA strands, reads the template strand in the 3′→5′ direction, and polymerizes complementary ribonucleoside triphosphates into an RNA chain in the 5′→3′ direction through phosphodiester-bond formation [1][2]. The resulting transcript has a nucleotide sequence complementary to the DNA template and corresponds, apart from uracil replacing thymine, to the coding-strand sequence. The process comprises ordered stages of promoter recognition and initiation, promoter escape, elongation of the nascent RNA, and termination with release of the RNA product and polymerase from the transcription unit [2][3]. Its molecular components include a DNA template containing regulatory and transcribed regions, RNA polymerase, ribonucleoside triphosphate substrates, divalent metal ions in the catalytic center, and accessory factors that direct polymerase recruitment, start-site selection, processivity, pausing, RNA processing, and termination [2][3][4]. In eukaryotes, RNA polymerases I, II, and III synthesize specialized RNA classes through associated transcription machineries, with RNA polymerase II producing precursor messenger RNAs and numerous regulatory non-coding RNAs [3][4].
  • 4
  • 23 Sep 2026
Topic Review
Transcription Elongation
Transcription elongation is the stage of RNA synthesis in which an RNA polymerase, assembled in a stable elongation complex with a DNA template and nascent RNA, moves along the template strand and sequentially incorporates ribonucleoside triphosphates into the 3′ end of the RNA molecule. Catalysis proceeds through template-directed base pairing, phosphodiester-bond formation at the polymerase active center, translocation of the enzyme–nucleic-acid complex, and displacement of the growing RNA transcript from the DNA–RNA hybrid [1][2]. The elongation complex maintains processive RNA synthesis while undergoing conformational changes and responding to sequence-encoded pause signals, DNA topology, chromatin or nucleoprotein structure, and associated elongation factors. In eukaryotic RNA polymerase II systems, phosphorylation of the C-terminal domain and recruitment of co-transcriptional RNA-processing and chromatin-associated factors form integral features of productive elongation [3].
  • 4
  • 24 Sep 2026
Topic Review
Transcription Termination
Transcription termination is the regulated completion of RNA synthesis at which an RNA polymerase ceases nucleotide addition, releases the nascent RNA transcript, and dissociates from the DNA template or transitions from the transcription unit through polymerase recycling pathways. It is executed by termination signals encoded in DNA and nascent RNA together with conformational changes in the transcription elongation complex and, in many systems, accessory proteins or RNA-processing complexes [1]. These molecular events destabilize the interactions among RNA polymerase, the RNA–DNA hybrid, the transcription bubble, and template DNA, thereby resolving the elongation complex at defined genomic positions [1][2]. In bacteria, termination includes intrinsic pathways directed by terminator RNA structures and uridine-rich RNA sequences, as well as pathways involving ATP-dependent RNA translocases such as Rho [2][3]. In eukaryotic RNA polymerase II transcription, cleavage of the nascent RNA at polyadenylation-associated sites and exonucleolytic degradation of the downstream RNA contribute to polymerase release [4].
  • 4
  • 24 Sep 2026
Topic Review
Cellular Engineering
Cellular engineering is the deliberate design, modification, preparation, and organization of living cells to generate controlled cellular behaviors and tissue-forming functions within tissue engineering and regenerative medicine. Its scope includes the selection and expansion of appropriate cell populations; modulation of cell phenotype, proliferation, survival, migration, differentiation, and secretory activity; and control of cell–cell and cell–extracellular-matrix interactions [1][2]. Cellular engineering integrates biochemical, genetic, and biophysical inputs, including soluble signaling factors, gene-delivery or genome-modification systems, biomaterial interfaces, mechanical stimuli, and spatial patterning, to establish defined cellular states and multicellular architectures [2][3][4]. In this context, cells constitute active biological components whose functions are specified through interactions with engineered microenvironments and with other cells during the formation, maintenance, or restoration of tissue-like organization [1][3].
  • 4
  • 24 Sep 2026
Topic Review
Protein Crystal Structures
Protein crystal structures are three-dimensional atomic models of proteins obtained by crystallographic analysis of protein crystals. A protein crystal contains a periodic array of ordered macromolecules, and X-ray diffraction from this array provides measured reflection intensities that are used to calculate electron-density maps. An atomic model is built and refined against these experimental data to specify the coordinates, occupancies, and atomic displacement parameters of the protein and any resolved ligands, cofactors, ions, solvent molecules, or ordered structural components [1][2]. The resulting structure defines the conformation and packing of the protein molecules within the crystallographic asymmetric unit and relates them through crystallographic symmetry to generate the unit cell and full crystal lattice [1][3]. Model interpretation incorporates experimental resolution, electron-density quality, stereochemical restraints, crystallographic residuals, and cross-validation statistics to quantify agreement between the atomic model and diffraction data [3][4].
  • 4
  • 28 Sep 2026
Topic Review
Fibrous Proteins
Fibrous proteins are structural proteins characterized by elongated polypeptide conformations, repetitive sequence organization, and assembly into ordered extracellular fibrils, fibers, microfibrils, or networks. In connective-tissue biology and the genetics of connective-tissue disorders, the term principally encompasses collagen proteins and the protein constituents of elastic fibers, including tropoelastin and fibrillin-containing microfibrils. Collagens contain glycine-rich repeating sequences that support triple-helical molecular organization and the formation of tissue-specific supramolecular matrices [1][2]. Their biosynthesis includes intracellular post-translational processing, secretion of procollagen, proteolytic maturation, fibril assembly, and covalent cross-link formation [2]. Elastic fibers contain a cross-linked elastin core formed from tropoelastin and a microfibrillar scaffold composed largely of fibrillin and associated extracellular proteins [3]. The genetic and biochemical scope of fibrous proteins includes the encoding genes, domain architecture, post-translational modifications, intermolecular interactions, and matrix assembly processes that determine connective-tissue structure [2][3][4].
  • 4
  • 24 Sep 2026
Topic Review
Hemoprotein
A hemoprotein is a protein whose molecular structure contains heme as an integral iron–porphyrin cofactor. Heme consists of a protoporphyrin IX macrocycle that coordinates a central iron ion; interactions between the iron, porphyrin, axial ligand residues, and surrounding amino acids establish the chemical and spectroscopic properties of the holoprotein [1][2]. The protein framework forms a heme-binding pocket that positions the cofactor, controls its coordination state and redox environment, and regulates access of small ligands or substrates [2]. Hemoproteins encompass globins, including hemoglobin, whose globin subunits each contain a heme group coordinated by a proximal histidine residue. In tetrameric hemoglobin, heme-containing subunits form an allosterically coupled assembly in which ligand binding is linked to conformational transitions and cooperative oxygen binding [3]. The term therefore covers the heme cofactor, its binding site, and the protein architecture that collectively specify heme-dependent molecular activity [1][2][3].
  • 4
  • 24 Sep 2026
Topic Review
Transcriptional Regulation
Transcriptional regulation is the set of molecular processes that determines the timing, cellular location, and rate at which defined genomic loci are transcribed into RNA. It operates through interactions among cis-regulatory DNA elements, including promoters, enhancers, silencers, and insulators; sequence-specific transcription factors; RNA polymerase and its general transcription machinery; cofactors; and the local chromatin environment [1][2]. Regulatory inputs influence the recruitment, assembly, activation, pausing, productive elongation, and termination behavior of RNA polymerase at individual transcription units. DNA accessibility, nucleosome positioning, histone modifications, DNA methylation, three-dimensional chromatin contacts, and regulatory non-coding RNAs contribute to the molecular state through which these inputs are integrated [2][3]. Within a gene regulatory network, transcriptional regulation comprises directed regulatory relationships in which transcriptional regulators modulate the transcriptional output of target genes, forming interconnected circuits that specify gene-expression programs [3].
  • 3
  • 24 Sep 2026
Topic Review
Enzyme Engineering
Enzyme engineering is the systematic alteration or design of an enzyme's molecular sequence, structure, or associated functional properties to generate enzyme variants with specified biochemical characteristics. It operates through controlled exploration of protein sequence and structural space using strategies including rational design, directed evolution, semi-rational design, computational protein design, and combinations of these approaches [1][2][3]. Rational strategies use structural, mechanistic, sequence, or computational information to identify molecular changes, whereas evolutionary methodologies generate genetic diversity followed by screening or selection of variants possessing specified phenotypes [1][2]. Semi-rational methods restrict diversification to residues or regions selected using prior structural or functional information [2]. The properties addressed within enzyme engineering can include catalytic activity, substrate specificity, selectivity, stability, cofactor dependence, reaction scope, expression, and other molecular characteristics of the enzyme. Iterative engineering commonly consists of sequence diversification or design, production of enzyme variants, functional characterization or selection, identification of advantageous sequence–function relationships, and subsequent rounds of molecular refinement [2][3]. 
  • 3
  • 27 Sep 2026
Topic Review
Enzyme Kinetics
Enzyme kinetics is the quantitative study of the rates and temporal behavior of enzyme-catalyzed reactions and of how those rates depend on concentrations of substrates, products, enzymes, inhibitors, activators, and relevant physicochemical conditions. It represents enzymatic reactions through kinetic schemes and rate equations describing the formation, interconversion, and decay of enzyme-associated molecular states. For a simple single-substrate reaction under appropriate steady-state conditions, kinetic behavior can be characterized by parameters including the maximum velocity (Vmax) the Michaelis constant (km) the catalytic constant (kcat) and the specificity parameter (kcat/ km) [1][2][3]. The field encompasses initial-rate and steady-state analysis, transient or pre-steady-state kinetics, inhibition kinetics, multi-substrate reaction kinetics, and analysis of complete reaction progress curves. These measurements and mathematical descriptions quantify catalytic turnover, substrate-dependent rate behavior, elementary or composite kinetic steps, enzyme saturation, and changes in reaction velocity arising from molecular interactions that affect the catalytic cycle [2][3]. 
  • 3
  • 27 Sep 2026
Topic Review
Genome Architecture
Genome architecture is the multiscale spatial organization of genomic DNA and chromatin within the cell nucleus, encompassing the physical arrangement, folding, and interaction patterns through which chromosomes occupy three-dimensional nuclear space. In eukaryotic cells, this organization comprises nested structural levels that include nucleosome-associated chromatin, chromatin loops, topologically associating domains, larger chromatin compartments, and chromosome territories [1][2][3]. Genome architecture is characterized by non-random contact frequencies among genomic regions and by dynamic transitions in chromatin configuration that occur while the underlying DNA sequence remains spatially organized within the nucleus [1][2]. Architectural organization is generated and maintained through the physical properties of chromatin together with molecular processes involving structural proteins such as cohesin and CTCF, chromatin-associated factors, transcriptional machinery, and epigenetic states [2][3][4]. The concept therefore covers the three-dimensional topology, hierarchical folding, spatial positioning, interaction domains, and dynamic conformational organization of the genome as a chromatin-based molecular system [3][4].
  • 3
  • 27 Sep 2026
Topic Review
Genome Mining
Genome mining is the systematic computational interrogation of genome sequence data to identify, annotate, and functionally infer genetically encoded biological features from characteristic sequence patterns and genomic organization. Within bioinformatics and molecular genomics, the process integrates sequence similarity searches, protein-domain recognition, motif analysis, gene-neighborhood information, comparative genomics, and specialized predictive algorithms to locate genes and coordinated genomic regions associated with defined molecular functions [1][2][3]. A major established form of genome mining identifies biosynthetic gene clusters, in which physically associated genes collectively encode enzymes, regulatory proteins, transport functions, and accessory components of a biosynthetic pathway [1][2]. Computational pipelines may classify these regions according to conserved biosynthetic domains, pathway architecture, similarity to characterized loci, and predicted enzymatic functions [1][3]. Genome mining therefore encompasses the extraction of biologically interpretable gene, pathway, and genomic-network information directly from assembled or annotated genome sequences through computational analysis and functional prediction [1][2][3].
  • 3
  • 28 Sep 2026
Topic Review
Diterpenoid
A diterpenoid is a member of a structurally diverse class of C20 terpenoid natural products whose carbon frameworks are biosynthetically derived predominantly from geranylgeranyl diphosphate (GGPP) and are associated with four isoprenyl units [1]. In plants, diterpenoid formation commonly begins with enzyme-catalyzed cyclization or rearrangement of GGPP by diterpene synthases, producing characteristic hydrocarbon or oxygenated scaffolds with acyclic, bicyclic, tricyclic, tetracyclic, or macrocyclic architectures [1][2][3]. These primary scaffolds undergo subsequent enzymatic elaboration involving reactions such as hydroxylation, oxidation, reduction, glycosylation, acylation, and other modifications that generate the molecular diversity of naturally occurring plant diterpenoids [2][3]. Their defining molecular scope therefore includes the twenty-carbon terpenoid framework, its biosynthetic derivation from isoprenoid precursors, scaffold formation through diterpene-synthase chemistry, and the resulting structural elaboration produced by downstream biosynthetic enzymes [1][2][3]. Within bioactive natural diterpenoid research, the term encompasses the molecular structures, biosynthetic pathways, and enzymatically generated chemical forms constituting this class of specialized plant metabolites [2][3].
  • 3
  • 28 Sep 2026
Topic Review
Intramolecular Dynamics
Intramolecular dynamics, within protein structure and dynamics, comprises the time-dependent internal motions and conformational transitions of atoms, residues, secondary-structure elements, loops, and domains within an individual protein molecule [1][2]. These motions arise from the protein's internal degrees of freedom and its conformational energy landscape, which permits the molecular structure to occupy an ensemble of interconverting conformational substates rather than a single invariant atomic configuration [1]. Intramolecular motions span a broad temporal range, including rapid bond and side-chain fluctuations, backbone rearrangements, loop movements, collective structural fluctuations, and slower transitions involving larger protein regions or domains [2][3]. Their molecular description includes the amplitudes of internal displacement, populations of conformational states, rates of exchange between states, correlations among atomic motions, and the energetic barriers separating accessible configurations. The concept therefore represents the dynamic component of protein molecular structure expressed through internal conformational fluctuations and transitions over time across multiple spatial and temporal scales [1][2][3].
  • 3
  • 27 Sep 2026
Topic Review
Enzyme Adaptation
Enzyme adaptation is the adjustment of enzyme molecular properties and enzymatic capacity that permits catalytic function to be maintained within the physicochemical conditions experienced by an organism. At the molecular level, adaptation can involve heritable changes in amino-acid sequence that modify protein conformational dynamics, structural stability, substrate binding, catalytic rate, and the dependence of these properties on environmental variables such as temperature, pressure, pH, or ionic conditions [1][2]. Such adaptation reflects selection on the relationship between enzyme structure and catalytic function, so that functionally relevant conformational states and kinetic properties occur within the environmental range in which the enzyme operates [2][3]. At the cellular and physiological level, enzyme adaptation can also encompass regulated changes in enzyme abundance or the expression of enzyme variants that alter total catalytic capacity under prevailing conditions. Its defining scope therefore includes adaptive modification of intrinsic enzyme properties—such as catalytic efficiency, ligand affinity, stability, and conformational flexibility—and regulated variation in the amount or molecular form of enzymatic activity available in cells [3][4]. These mechanisms collectively establish an enzyme system whose catalytic behavior is compatible with the organism's biochemical and physicochemical environment [2][4].
  • 2
  • 28 Sep 2026
Topic Review
Enzyme Binding Dynamics
Enzyme binding dynamics encompasses the time-dependent molecular processes through which an enzyme associates with, interacts with, conformationally responds to, and dissociates from a binding partner such as a substrate, inhibitor, cofactor, or regulatory ligand. Binding occurs within an ensemble of interconverting enzyme conformations, and transitions among these conformational substates can alter the accessibility, geometry, and physicochemical properties of binding sites [1][2]. The concept includes the kinetics of molecular association and dissociation, transient enzyme–ligand configurations, conformational exchange accompanying complex formation, and fluctuations within the bound complex. These processes span multiple temporal and spatial scales, from local atomic and side-chain fluctuations to larger loop or domain rearrangements [2][3]. Enzyme binding dynamics therefore describes binding as a molecular trajectory through conformational and interaction states whose populations and interconversion rates determine how ligand recognition and occupancy develop over time [1][3]. Within enzyme function and inhibition, its scope encompasses substrate, product, cofactor, activator, and inhibitor interactions insofar as their association, residence, conformational coupling, and release are properties of the enzyme–ligand binding process [2][4].
  • 2
  • 28 Sep 2026
Topic Review
Enzyme Modification
Enzyme modification is the alteration of an enzyme's molecular structure through covalent or other chemically defined changes that modify the structural or functional state of the enzyme. Within molecular enzymology, such modification encompasses changes to amino-acid side chains, protein termini, prosthetic or cofactor-associated groups, and other chemically accessible sites that can alter catalytic activity, substrate recognition, conformational behavior, stability, localization, molecular interactions, or susceptibility to inhibition and regulation [1][2]. Modification may arise through biologically controlled covalent processing, including phosphorylation, acetylation, glycosylation, ubiquitination, proteolytic processing, and related post-translational reactions, or through experimentally introduced chemical transformations such as residue-selective derivatization, conjugation, crosslinking, and incorporation of noncanonical chemical functionalities. A modification is characterized by the chemical identity of the structural change, its molecular site or sites, its stoichiometry and reversibility where applicable, and the resulting state of the enzyme molecule [1][2][3]. Functionally relevant enzyme modification consequently encompasses molecular changes capable of altering active-site properties, conformational equilibria, intermolecular interactions, or other structural determinants of enzymatic activity [2][3]. 
  • 2
  • 27 Sep 2026
  • Page
  • of
  • 135
Featured Entry Collections
>>

Featured Reprints

>>
Encyclopedia of Digital Society, Industry 5.0 and Smart City
Encyclopedia of Engineering
Encyclopedia of Social Sciences
Encyclopedia of Medieval Royal Iconography
Academic Video Service
Feedback