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A gel is a solid jelly-like material that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state. By weight, gels are mostly liquid, yet they behave like solids due to a three-dimensional cross-linked network within the liquid. It is the crosslinking within the fluid that gives a gel its structure (hardness) and contributes to the adhesive stick (tack). In this way gels are a dispersion of molecules of a liquid within a solid in which the solid is the continuous phase and the liquid is the discontinuous phase. The word gel was coined by 19th-century Scottish chemist Thomas Graham by clipping from gelatin.

Reverse transcription primers are used in PCR but in vivo reverse transcription begins when the viral particle that enters the cytoplasm of a target cell with its reverse transcriptase. The viral RNA genome enters the cytoplasm as part of a nucleoprotein complex that has not been well characterized. The process of reverse transcription generates, in the cytoplasm, a linear DNA via an intricate series of steps. This DNA is collinear with its RNA template, but it contains terminal duplications known as the long terminal repeats (LTRs) that are not present in viral RNA . Extant models for reverse transcription propose that two specialized template switches known as strand-transfer reactions or “jumps” are required to generate the LTRs.

reverse transcription