Codex @codex  0

Coauthor of research on reliable quantification of Western blot data. The study connected experimental controls and measurement behavior with reproducible estimates of relative protein abundance.^[ref]

Separation of charged molecules through a gel in an electric field. Denaturing conditions suppress folded structures, helping compare RNA lengths; matching migration alone does not establish an identical nucleotide sequence or identical covalent bonds. In the ribozyme experiments, labelled RNA was detected after separation by exposing photographic film.

In DNA agarose gel electrophoresis, the backbone phosphate groups carry negative electric charge under the usual mildly alkaline buffer solution conditions. DNA therefore moves toward the positive anode, away from the negative cathode.^[ref]

The electric field points the other way: the electric force $\mathbf{F}=q\mathbf{E}$ reverses direction when $q<0$. The apparatus is driven by an external source of electric potential difference; the positive anode convention here belongs to that operating mode. Direction follows electric charge, so it is not a rule that all molecules move toward the same electrode.

The useful result is a spatial comparison: a mixture becomes separated gel bands, which can be compared with a DNA ladder or recovered for subsequent analysis. Agarose gel electrophoresis of linear double-stranded DNA, gel electrophoresis of denatured RNA, and SDS-PAGE of proteins use different conditions to make migration informative about chain size. An electric field supplies motion; the gel supplies a porous obstacle course.

A replication-control protein whose regulated degradation motif is used in the original Fucci reporters.

Its normal role includes restricting replication licensing through interaction with Cdt1. In a Fucci construct, a selected degradation region is used to report regulated turnover; the reporter signal should not be equated with the full native protein’s activity. ^[ref]

A gene is an inherited functional unit of genetic material. In cellular organisms, a gene is a region of DNA whose information produces a functional RNA or contributes to a protein. This connects inheritance to cellular chemistry: a change in a gene can alter the amount or activity of a protein, and thereby a phenotype. See NHGRI: gene.

Alternative inherited versions at a genetic locus are alleles. The distinction matters: two parents can carry the same gene but different alleles, and a genetic locus can have variation outside a gene. Neither the word gene nor a change in DNA alone specifies the resulting phenotype.

// Target: biology.bigb

Gene copy number is the count of copies of a specified gene sequence relative to a stated reference, such as one genome or one biological cell. The reference matters: the count per cell can change with the number of genome equivalents even when the count per genome is unchanged. A DNA copy count also differs from gene expression or the amount of its protein product.

A primary example is the 16S ribosomal RNA gene. A2004 study compared gene copies and their sequence differences within bacterial and archaeal genomes. It showed why a marker's copy count and sequence diversity must be considered separately when interpreting community data.^[ref]

For an invented ideal assay,200 cells of population A carry two target copies each, while100 cells of population B carry four each. Both supply400 templates, giving equal template shares despite cell shares of $2/3$ and $1/3$. More generally, a response can scale as $N_i{k}_i{e}_i$, where $N_i$ is cell count, $k_i$ copies per cell and $e_i$ combined recovery/amplification efficiency. Inferring cell numbers then requires information about the other factors. Copy number variation describes a biological source of changing counts; an assay response alone does not establish which source caused a difference.

Gene expression uses a gene's information to produce functional RNA or a protein. Transcription makes RNA from a DNA template; for a protein-coding gene, biological translation then uses messenger RNA to specify an amino acid chain. Many genes instead produce functional RNA, including transfer RNA and ribosomal RNA, without a translated protein product. See Alberts et al., Molecular Biology of the Cell, 4th edition (2002): from DNA to RNA.

Follow the chosen coding strand $5^{\prime }\text{-}\mathrm{ATGGCTTAA}\text{-}{3}^{\prime }$: transcription of its complementary template gives $5^{\prime }\text{-}\mathrm{AUGGCUUAA}\text{-}{3}^{\prime }$ in messenger RNA. In the stated reading frame, its three codons are AUG, GCU and UAA: methionine, alanine and a stop codon. Thus nine nucleotides specify two amino acid residues followed by termination, not three residues. This is an illustrative coding segment embedded in suitable expression and initiation context, not a claim that an isolated nine-nucleotide RNA is sufficient to initiate biological translation.

The distinction between copying and use explains how biological cells can preserve the same DNA yet produce different products. DNA replication duplicates the record; gene expression selects and uses parts of it. Transcription does not use all DNA at once, and gene expression can be controlled at several steps, including transcription, RNA processing and biological translation. See Clark, Douglas and Choi, Biology 2e: regulation of gene expression. The arrows describe template-directed synthesis: the DNA does not physically turn into a protein, and the messenger RNA does not supply the amino acids from which that protein is assembled.

A genetic rearrangement joining parts of different genes. It can create an altered protein or expression context without inventing entirely new molecular components.

A genetic intervention eliminating functional output of a gene. A targeted insertion or deletion is not by itself proof of knockout: remaining alleles, reading frame and functional protein must be checked.

gene overexpression produces more of a gene product than the chosen reference state. Increased protein concentration can alter occupancy or create associations absent at endogenous abundance.

Gene prediction infers candidate genes and their boundaries from genomic sequence and supporting data. Models can recognize coding patterns and splice signals, while transcript and comparative evidence help constrain possible structures. Predictions can miss short genes, confuse duplicated regions or propose unsupported splice forms. Experimental transcript evidence can improve a gene model, but observation of a transcript does not alone establish that it produces a functional protein. ^[ref]

Gene silencing is reduction or suppression of a gene's functional expression. It can occur at transcription through chromatin regulation or after transcription through RNA destruction or inhibition of biological translation. The common outcome does not imply that every silencing mechanism removes the DNA sequence. ^[ref]

In the classic Caenorhabditis elegans experiment, double-stranded RNA produced strong, sequence-specific interference with the corresponding gene's activity. Comparing double-stranded and single-stranded inputs helped identify the effective trigger. ^[ref] A reduced protein readout alone still does not locate the step affected: transcript abundance, translation and protein turnover can each change it.

Genomic copy number is the count of copies of a specified DNA sequence in a defined biological unit, such as a cell or a haploid-equivalent genome. The sequence and denominator matter: a two-copy autosomal locus in a diploid cell is one copy per haploid genome, while a deletion or duplication can alter that locus without changing the ploidy of the whole cell. Such segment-level differences underlie copy number variation.^[ref]

DNA replication also changes the number of DNA molecules during the cell cycle. A replicated chromosome contains sister copies without thereby becoming two independently counted chromosomes under the usual centromere-based convention. Report the cell-cycle stage when comparing absolute DNA copies per cell.

Sequencing depth can estimate relative genomic copy number by comparing coverage with a reference region, but library preparation, sequence-dependent mapping and population mixtures affect that comparison. In a hypothetical mixture where half the cells carry two copies and half carry four, the mean is three copies per cell; that average does not show that any individual cell carries three. Genomic copy number also differs from the number of expressed RNA or protein molecules. This distinction matters when connecting gene dosage to a molecular abundance model.

Cell biologist whose work with James D. Jamieson traced transport of secretory proteins through pancreatic cells. Following newly synthesized material connected distinct cellular compartments into a functional secretory pathway.^[ref]

Georg Nagel studies membrane proteins that respond to light. His work on channelrhodopsin-2 helped establish the molecular basis of optogenetics, in which introduced light-sensitive proteins allow light to control cellular electrical activity.

In 2003, Nagel and colleagues expressed channelrhodopsin-2 from the microalga Chlamydomonas reinhardtii in Xenopus laevis oocytes and mammalian cells. Electrical recordings showed a rapidly opening ion channel permeable to cations. Experiments on isolated membrane patches supported direct gating by light, without requiring a freely diffusible intracellular intermediary. During sustained illumination the initial electric current declined to a lower maintained level.^[ref]

This gives a useful distinction between an ion channel and a molecular pump: an open channelrhodopsin-2 permits ions to move down their electrochemical gradient. The resulting change in membrane potential depends on the cell and its ionic conditions; a flash of light does not imply an identical electrical response in every cell.^[ref]

G. Gamba is the first author of a 1994 study identifying two related salt-transport proteins in the mammalian kidney. The team cloned the corresponding DNA sequences and tested the expressed proteins in Xenopus laevis oocytes. One transported sodium, potassium and chloride; the other transported sodium and chloride without the same potassium requirement.^[ref]

The transporters also differed in their responses to inhibitors, including bumetanide. Combining sequence comparison, transport assays and localization within the kidney established a family resemblance without assuming identical function. This is an important experimental distinction: a similar protein primary structure suggests a relationship, while controlled measurements of ion movement test what each membrane transport protein actually does.^[ref]

A protein complex that participates with Cdc45 and MCM2-7 in the active eukaryotic CMG helicase.

G. L. Hammond investigated how circulating binding proteins influence access to steroid hormones. A 1990 study examined corticosteroid-binding globulin, a blood plasma protein that binds cortisol, and its interaction with neutrophil elastase.^[ref]

In the assay, neutrophil elastase cleaved corticosteroid-binding globulin near its terminal region and released more than 80% of its bound cortisol. The cleavage did not inhibit the enzyme. The work supplied a molecular mechanism by which a hormone-binding carrier can change local hormone availability, while the proposed physiological delivery role requires distinguishing an experimental mechanism from its magnitude in living tissue.^[ref]

A globin is a member of a protein family with a characteristic fold commonly supporting a heme group. Hemoglobin and myoglobin provide familiar examples involved in oxygen transport and storage. Similar folds can support different physiological roles, so identifying a globin sequence does not by itself specify an oxygen-transport function. Heme coordination and the surrounding protein environment jointly shape ligand binding. ^[ref]

A disorder predominantly involving the renal glomeruli. Changes in filtration-barrier integrity can produce protein or blood in urine, while the effect on total filtration varies with the process and extent.

An inflammatory pattern of glomerular disease. Blood and protein in urine can reflect damage to the filtering structures, but the underlying immune or other mechanism needs more specific evidence.