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Showing 1681–1709 of 1709 reference entries

Measurement · PhysicsRadiant flux, intensity, irradiance, exitance and radiance

Optical power, directional power and surface densities are different quantities.

DefinitionMeasurement · PhysicsPhotometric weighting, lumen, candela, lux and luminance

Photometry weights radiation with a specified standard visual response.

DefinitionMeasurementWriting SI quantities and unit symbols

Symbol form, spacing and parentheses preserve the meaning of reported quantities.

DefinitionMeasurementGram prefixes and the kilogram exception

Mass prefixes attach to gram even though kilogram is the SI base unit.

DefinitionMeasurementRounding a result with its uncertainty

Report useful digits without treating extra digits as proof of accuracy.

MethodMeasurement · Physics · ChemistryCommon non-SI units and exact SI conversions

Common non-SI unit names require their correct SI scale factors.

DefinitionPhysics · ChemistryGas pressure as molecular momentum transfer

Molecular collisions link macroscopic pressure to random translational motion.

ModelChemistry · PhysicsOrdinary aggregate states and bulk behavior

Solid, liquid and gas describe bulk behavior rather than chemical identity.

ModelChemistryInferring empirical and molecular formulas from composition

Element mass ratios become atom ratios through molar masses, with uncertainty and sample identity retained.

MethodChemistryLewis structures and valence-electron accounting

A Lewis diagram accounts for bonding and nonbonding valence electrons in a specified connectivity.

MethodChemistryElectron-domain geometry and molecular shape

VSEPR distinguishes the arrangement of electron regions from the positions of atoms.

ModelChemistryElectronegativity, bond polarity and molecular polarity

Polar bonds can cancel in a molecule; molecular geometry matters.

ModelChemistrySolutions, solutes, solvents and solvation

Dissolution disperses specified molecular or ionic species in a solvent.

DefinitionChemistrySolubility, saturation and supersaturation

A saturation limit is an equilibrium property under specified conditions, not a synonym for concentration.

DefinitionChemistryFiltration separates retained solids from a fluid

Ordinary filtration separates undissolved particles; dissolved species can remain in the filtrate.

MethodChemistryDistillation and vapor–liquid composition

Distillation uses vapor–liquid partitioning and condensation, with a limit at an azeotrope.

MethodBiologyGene, allele, genotype and phenotype

Genomic sequence variants and observable traits describe different levels of biological information.

DefinitionBiology · ChemistryEnzyme substrates, active sites and induced fit

Substrate recognition and catalysis depend on a dynamic molecular environment.

ModelBiology · ChemistryMonomers, polymers and hydrolysis

Covalent subunit linkage and water-assisted cleavage explain biological polymer structure.

DefinitionBiology · ChemistrySugars, glycosidic linkages and polysaccharides

Sugar connectivity distinguishes energy-storage and structural polysaccharides.

DefinitionBiology · ChemistryFatty acids, storage lipids and membrane lipids

Lipids include several architectures rather than one repeating-monomer polymer class.

DefinitionBiology · ChemistryAmino-acid residues and peptide linkages

The peptide backbone and variable side chains are different parts of protein structure.

DefinitionBiology · ChemistryNucleotides and DNA/RNA backbone polarity

Bases carry sequence information on a chemically directional sugar–phosphate backbone.

DefinitionBiologyCell membrane, cell wall, cytosol and compartments

A cell's boundary, fluid interior and specialized structures have different roles.

DefinitionEarth & cosmos · MeasurementEarthquake location, source magnitude and local intensity

A source location or magnitude does not describe the shaking experienced at every site.

DefinitionEarth & cosmosAtmospheric composition and thermal layers

Composition and temperature structure describe different features of Earth's atmosphere.

ModelEarth & cosmosDrainage basins, outlets and water divides

Surface drainage boundaries depend on the chosen outlet and need not bound groundwater flow.

DefinitionEarth & cosmosThe celestial sphere and the observer's sky

A sky direction is an angular observation, not an object's three-dimensional distance.

ModelEarth & cosmos · MeasurementRight ascension, declination and reference epochs

Celestial angular coordinates require a declared reference system and date conventions.

Definition
DefinitionSource checked

Nucleotides and DNA/RNA backbone polarity

BiologyChemistry

Bases carry sequence information on a chemically directional sugar–phosphate backbone.

Key knowledge

A nucleotide contains a base, a pentose sugar and one or more phosphate groups. DNA uses deoxyribose, with hydrogen at sugar carbon 2′; RNA uses ribose, with a 2′ hydroxyl. Their usual bases are A, G and C with T in DNA and U in RNA. In ordinary DNA/RNA chains, 3′–5′ phosphodiester linkages connect sugars through phosphate, giving backbone directionality. The two strands of the usual DNA double helix are antiparallel; RNA can also fold by internal base pairing.

Conditions and scope

  • Canonical backbone and common bases; modified bases and other nucleic-acid chemistries also exist.
  • Sugar–phosphate covalent linkage and base-pair hydrogen bonding are different interactions; RNA is not required to remain an unstructured single strand.
Sources · 2

References

Sources retain their recorded scope. A source link alone does not establish verification of every statement.

  1. Biology 2e (2018), §3.5 Nucleic acidsMary Ann Clark, Matthew Douglas and Jung Choi · OpenStax/Rice UniversityTextbook chapteropenstax.orgRead source
  2. Biology XII: Molecular Basis of InheritanceNCERTTextbook chapter · PDFncert.gov.inRead source

Evidence and review

Nucleotide components, ribose/deoxyribose distinction and chemical directionality of the common DNA/RNA backbones.

2026-10-10 · Independent Mathematics and Information editor (AI editorial/source review; not the Chemistry/Biology/Earth author). The specified introductory inventory has no unresolved demonstrated material gap after the changes and body-based reuse. Existing advanced references retain their historical scoped approvals. English-only reference prose and explicit Lithuanian-translation-pending status are preserved.

Foundational review

2026-10-10 · Independent AI editorial inspection of this new compact reference entry, its equations, applicability, sources and knowledge connections.

Sources from other places

Agreement within this scope

Base/sugar/phosphate composition, 3′–5′ links and antiparallel DNA.

DNA and RNA differ in sugar chemistry and usual pyrimidine bases.

  • NCERT

    • Biology XII: Molecular Basis of Inheritance
      IndiaEnglish

      §5.1.1, printed pp80–82: DNA/RNA backbone and base pairing; §5.4, printed pp88–90: semiconservative replication; §5.5.2–5.5.3, printed pp92–95: transcription and RNA products; §5.7, printed pp98–100: translation and activated amino acids

Related reference entries

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Scientific relationships · 2 / 2

The relationship type describes the connection. Its linked statements, sources and conditions define the scope.

  1. Related to
    Relationship sources · 1

    Linked statements

    • A nucleotide contains a base, a pentose sugar and one or more phosphate groups. DNA uses deoxyribose, with hydrogen at sugar carbon 2′; RNA uses ribose, with a 2′ hydroxyl. Their usual bases are A, G and C with T in DNA and U in RNA. In ordinary DNA/RNA chains, 3′–5′ phosphodiester linkages connect sugars through phosphate, giving backbone directionality. The two strands of the usual DNA double helix are antiparallel; RNA can also fold by internal base pairing.

    DNA base sequence is carried on a directional covalent sugar–phosphate backbone distinct from interstrand pairing.

  2. Related to
    Relationship sources · 1

    Linked statements

    • A nucleotide contains a base, a pentose sugar and one or more phosphate groups. DNA uses deoxyribose, with hydrogen at sugar carbon 2′; RNA uses ribose, with a 2′ hydroxyl. Their usual bases are A, G and C with T in DNA and U in RNA. In ordinary DNA/RNA chains, 3′–5′ phosphodiester linkages connect sugars through phosphate, giving backbone directionality. The two strands of the usual DNA double helix are antiparallel; RNA can also fold by internal base pairing.

    Backbone polarity defines the 3′ end extended during ordinary DNA synthesis.

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