Biotechnology Terms Starting With F
Biotechnology Glossary: F
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FACS
/ FAKS / · Acronym from Fluorescence-Activated Cell Sorting, coined in early 1970s
FACS, short for fluorescence-activated cell sorting, is a specialized flow cytometry technique that physically separates individual cells from a heterogeneous mixture based on fluorescent labeling and light-scattering properties.
FACS isolates specific cell populations at rates exceeding 50,000 cells per second with purities above 95 percent. Laser excitation detects fluorescently labeled antibodies bound to cell-surface markers, and the instrument then applies electrostatic charges to deflect target cells into collection tubes. Modern instruments can simultaneously analyze up to 18 fluorescent parameters, enabling highly refined population isolation.
The technique advanced immunology in the 1980s by allowing precise analysis of T cell and B cell populations based on CD marker expression, work that depended on the ability to collect living, sorted cells for downstream experiments.
The first commercial FACS instrument, developed by Becton Dickinson and released in 1974, cost the equivalent of over $500,000 in today's currency, limiting access to major research institutions. Some current systems sort single cells directly into individual wells of 384-well plates for clonal expansion or single-cell sequencing.
FACS and flow cytometry describe the same procedure. Flow cytometry measures fluorescence and scatter signals from cells passing through a laser but does not physically separate them; FACS adds an electrostatic deflection step that collects defined populations into separate tubes.
Researchers at Stanford University used FACS to isolate hematopoietic stem cells from human bone marrow based on CD34-positive and CD38-negative surface markers, achieving purities greater than 98 percent. True stem cells represented fewer than 0.1 percent of total bone marrow cells in those preparations, demonstrating how FACS recovers rare populations that bulk methods cannot reach.
Flow Cytometry
/ floh sy-TOM-eh-tree / · Old English flowan; Greek kytos, cell; metron, measure
Flow cytometry is a technique that measures physical and chemical properties of individual cells as they pass single-file through a laser beam, enabling rapid, multiparameter analysis of thousands of cells per second.
Cells are labeled with fluorescent antibodies or dyes targeting surface markers, intracellular proteins, or DNA content, and each cell’s fluorescence intensity is recorded simultaneously across multiple parameters. Fluorescence-activated cell sorting extends the technique by adding an electrostatic deflection step that physically isolates specific populations based on their fluorescence profile. Modern clinical instruments routinely distinguish more than 10 cell populations in a single blood sample, making flow cytometry indispensable for immunology, cancer diagnosis, and quality control of cell-based biopharmaceuticals.
The first practical flow cytometer was built by Mack Fulwyler in 1965 at Los Alamos National Laboratory, using ink-jet printer technology adapted to sort cells by volume.
Researchers at the Karolinska Institute used flow cytometry to show that regulatory T cells expressing the FOXP3 transcription factor constitute roughly 5 to 10 percent of circulating CD4-positive T cells in healthy adults, a proportion that drops measurably in patients with certain autoimmune diseases.
Flow cytometry examines cells the way a microscope examines a tissue slide. Flow cytometry analyzes cells suspended individually in a fluid stream, measuring one cell at a time as it passes a laser, rather than imaging cells arranged on a fixed surface.
Clinicians use flow cytometry to count CD4-positive T cells in blood samples from people living with HIV. A count below 200 cells per microliter of blood meets one diagnostic criterion for AIDS, so the measurement directly guides treatment decisions.
Functional Annotation
/ FUNK-shun-ul an-oh-TAY-shun / · Latin functio, performance; annotare, to mark
Functional annotation is the process of assigning biological meaning, including predicted function, pathway membership, and phenotypic effects, to genes and other genomic features identified by sequencing.
Annotation combines computational prediction, using homology to characterized genes and conserved domain identification, with experimental validation through mutant phenotyping, proteomics, and transcriptomics. Gene Ontology terms provide a standardized vocabulary for describing molecular function, biological process, and cellular component attributes of gene products, allowing databases across species to use consistent labels. Despite decades of effort, roughly 20 percent of genes in the well-studied budding yeast Saccharomyces cerevisiae still lack reliable functional annotation, and the proportion is far higher in less-studied organisms.
Automated pipelines such as those used by the NCBI RefSeq project annotate millions of sequences, but each computational assignment carries a confidence score that reflects the strength of the underlying evidence.
When the genome of the bacterium Mycoplasma genitalium was fully sequenced in 1995, researchers found that approximately 170 of its 525 protein-coding genes had no assignable function based on sequence similarity alone, a gap that took years of targeted experiments to begin closing.
Protein Domains →A computer-generated gene annotation is a confirmed biological fact. Most annotations are computational predictions based on sequence similarity, and similar sequences can sometimes carry out different functions, so experimental confirmation remains necessary before a predicted role is accepted.
After sequencing the genome of a newly isolated soil bacterium, annotation software may label a gene as a beta-lactamase based on greater than 80 percent amino acid identity to a characterized enzyme. Researchers then test whether the gene confers resistance to ampicillin in a susceptible host strain to confirm the predicted function.
Are Enzymes Proteins? →Fusion Protein
/ FYOO-zhun PROH-teen / · From Latin fusio, a pouring or melting, plus protein from French protéine
Fusion Protein is a protein engineered by joining two or more genes that originally coded for separate proteins, producing a single polypeptide with combined functional properties.
Fusion proteins combine functional domains from different proteins to create novel therapeutic agents or research tools. The pharmaceutical industry has produced more than 30 FDA-approved fusion protein drugs, including etanercept for rheumatoid arthritis, which fuses a TNF receptor to an antibody Fc fragment and carries a plasma half-life of approximately 102 hours compared to just 4 hours for the natural receptor. Common laboratory fusion tags include glutathione S-transferase, maltose-binding protein, and green fluorescent protein, which aid in purification or visualization of target proteins.
Production typically involves cloning genes in-frame within expression vectors, directing host cells such as E. coli or CHO cells to synthesize the combined polypeptide.
Some bacteria naturally produce bifunctional fusion proteins as a metabolic strategy. In Neurospora crassa, the arom protein is a single polypeptide that carries five consecutive enzymatic activities of the shikimate pathway, a natural fusion that channels intermediates directly between active sites without releasing them into the cytoplasm.
Fusion proteins are genetically modified organisms. Fusion proteins are purified molecules produced inside GMO host cells; the protein itself is not a living organism and cannot reproduce or spread in the environment.
Scientists at Genentech engineered etanercept by joining the coding sequence for the p75 TNF receptor to the Fc region of human IgG1. The resulting fusion protein binds two TNF molecules simultaneously, and its 102-hour half-life in circulation is roughly 25 times longer than that of the unmodified receptor.