In vitro (Latin: within the glass) refers to the technique of performing a given experiment in a controlled environment outside of a living organism; for example in a test tube. In vitro fertilization is a well-known example of this. Many experiments in cellular biology are conducted outside of organisms or cells; because the test conditions may not correspond to the conditions inside of the organism, this may lead to results that do not correspond to the situation that arises in a living organism. Consequently, such experimental results are often annotated with in vitro, in contradistinction with in vivo .

In vitro research

This type of research aims at describing the effects of an experimental variable on a subset of an organism's constituent parts. It tends to focus on organs, tissues, cells, cellular components, proteins, and/or biomolecules. Overall, it is better suited for deducing the mechanisms of action (See in vivo for its description and respective merits). With fewer variables and perceptually amplified reactions to subtle causes, results are generally more discernible.

The massive adoption of low-cost in vitro molecular biology techniques has caused a shift away from in vivo research which is more idiosyncratic and expensive in comparison to its molecular counterpart. Currently, in vitro research is both vital and highly productive.

However, the controlled conditions present in the in vitro system differ significantly from those in vivo and may give misleading results therefore in vitro studies are usually followed by in vivo studies. Examples include:

• In biochemistry, non-physiological stoichiometric concentration may result in enzymatic active in a reverse direction, hence for historical reasons several enzyme in the Krebs cycle may appear to have incorrect nomeclature.
• DNA may adopt other configurations, such as A-DNA.
• Protein folding may differ as in a cell there is a high density of other protein and there are systems to aid in the folding, while in vitro the conditions are less clustered and not aided.

It should be pointed out that the term is historical, as currently most labware is disposable and made out of polypropylene (sterelizable by autoclaving such as microcentrifuge tubes) or clear polystyrene (such as sierotological pipettes) rather than glass in order to ease labwork, ensure sterility and minimize the possibility of cuts due to broken glass.

See also

• Animal testing
• Ex vivo
• In situ
• In utero
• In vivo
• In silico
• In vitro fertilization

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