Biotechnology Terms Starting With O
Biotechnology Glossary: O
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Off-Target Effect
/ AWF-TAR-get eh-FEKT / · From Old English of, away from, and Old French targette, small shield, combined with Latin effectus, accomplishment or result.
Off-Target Effect off-target effect is an unintended genetic change or molecular interaction that occurs at a location in the genome other than where a gene-editing tool like CRISPR was supposed to make its cut.
Off-target effects represent a major challenge in CRISPR-Cas9 gene editing because the guide RNA can tolerate 1 to 5 mismatches and still direct cutting at similar genomic sequences. Studies using whole-genome sequencing have detected off-target mutations occurring at frequencies ranging from undetectable to over 50% depending on the guide RNA design and Cas9 variant used. High-fidelity Cas9 variants like SpCas9-HF1 and eSpCas9 reduce off-target activity by 10 to 100-fold compared to wild-type Cas9.
In drug development, off-target binding of small molecules to unintended proteins causes many adverse side effects and limits therapeutic indices. Computational tools like Cutting Frequency Determination and GUIDE-seq help predict and detect off-target sites before clinical application.
The most common off-target sites for CRISPR typically differ by only 1 to 3 nucleotides from the intended target and are located in gene-poor regions of the genome. Some guide RNAs have shown zero detectable off-target effects even in sensitive whole-genome screens, while others create dozens of unintended edits.
Off-target effects only occur in gene editing technologies like CRISPR. They are equally problematic in RNA interference, where short interfering RNAs can silence unintended transcripts, and in antisense oligonucleotide therapies, where partial complementarity to non-target sequences causes unintended knockdown.
In 2018, researchers at the Francis Crick Institute discovered that CRISPR editing in human embryos produced large deletions and complex rearrangements at off-target sites up to several kilobases away from the intended cut site. Base editors and prime editors have emerged as alternatives that show dramatically reduced off-target effects in therapeutic applications targeting sickle cell disease.
Oligonucleotide Synthesis
/ ol-ih-goh-nyoo-KLEE-oh-tyd SIN-theh-sis / · Greek oligos, few; Latin nucleus; Greek synthesis, putting together
Oligonucleotide synthesis is the chemical process of assembling short, single-stranded DNA or RNA molecules of defined sequence using automated phosphoramidite chemistry on a solid support.
Synthesis cycles add one nucleotide at a time in a defined order, achieving near-quantitative coupling efficiency at each step; a 20-mer oligonucleotide typically takes under an hour to synthesize. Oligonucleotides serve as PCR primers, hybridization probes, CRISPR guide RNAs, antisense therapeutics, and building blocks for synthetic genes. Array-based oligonucleotide synthesis now enables the parallel production of thousands of distinct sequences in a single run.
Oligonucleotide synthesis builds short DNA or RNA strands with a chosen sequence. These custom molecules are basic tools for PCR, probes, sequencing, and gene editing.
Building Blocks of Nucleic Acids →All DNA used in labs must be copied from living cells. Short DNA pieces can be chemically synthesized from nucleotide building blocks.
A lab can order synthetic primers for a PCR test. The primer sequences are designed to match the DNA region being amplified.
Organ on a Chip
/ OR-gan on a CHIP / · Latin organum; Middle English on; microchip
Organ on a Chip organ on a chip is a microfluidic cell culture device lined with living human cells that replicates the microarchitecture and physiological functions of a human organ for drug testing and disease modeling.
These devices use tiny channels molded in transparent polymer to create compartmentalized chambers where cells experience fluid flow, mechanical stretch, and cell-cell interactions that mimic in vivo conditions far better than flat cell culture. Organ chip platforms for lung, gut, kidney, liver, heart, and brain have been developed and validated against in vivo drug responses. Linked multi-organ chips create a body-on-a-chip system that can model pharmacokinetics and organ cross-talk across multiple tissues.
An organ on a chip uses living cells in tiny channels to mimic selected features of an organ. It can include fluid flow, stretching, or tissue barriers.
An organ on a chip is a complete miniature organ. It models certain functions, not every structure and behavior of the real organ.
A lung-on-a-chip can culture airway and blood-vessel cells on opposite sides of a flexible membrane. Researchers use it to study inflammation, infection, or drug effects.
Respiratory System Fun Facts →Overexpression
/ OH-vur-ek-SPRESH-un / · From Old English ofer, meaning excessive or beyond, and Latin expressio, pressing out or manifestation.
Overexpression is the production of a gene product at levels significantly higher than normal through genetic manipulation or abnormal cellular conditions.
Overexpression is achieved by introducing multiple gene copies, using strong promoters, or removing regulatory elements that normally limit expression. Researchers routinely use expression vectors containing the T7, CMV, or EF1? promoters to drive high-level protein production in bacterial, mammalian, or yeast expression systems.
In biotechnology applications, overexpression can increase yields of therapeutic proteins like insulin by 1000-fold compared to native expression levels. The technique allows scientists to study protein function, produce industrial enzymes, and manufacture biopharmaceuticals at commercial scales. However, excessive overexpression can trigger cellular stress responses, protein misfolding, or metabolic burden that reduces cell viability and product quality.
Some cancer cells naturally overexpress the HER2 protein by up to 100 times normal levels, which led to the development of Herceptin, a targeted therapy that specifically binds this overexpressed protein. Chinese hamster ovary cells, the workhorses of biopharmaceutical production, can be engineered to overexpress recombinant proteins to levels exceeding 5 grams per liter of culture.
More gene expression always produces more functional protein. Extreme overexpression frequently causes misfolding, aggregation into inclusion bodies, or toxicity to the host cell, which is why optimizing promoter strength and codon usage is essential for productive recombinant protein production.
Escherichia coli bacteria are routinely engineered to overexpress human insulin using the lac operon promoter system, producing up to 30% of total cellular protein as recombinant insulin. Pharmaceutical companies like Genentech use overexpression systems in large-scale bioreactors to manufacture therapeutic antibodies that would naturally exist at only trace amounts in the human body.