g-radiation and X-rays (ionizing radiation) are particularly hazardous because they cause double-strand breaks in the DNA, which are difficult to repair. If left unrepaired, double-strand breaks can be lethal to a cell.

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#Unit 13. Methods in Biology

The polymerization of acrylamide is an example of free-radical catalysis and is initiated by the addition of ammonium persulfate and the base N,N,N′,N′-tetramethylenediamine ( TEMED

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#Unit 13. Methods in Biology

TEMED catalyzes the decomposition of the persulfate ion to give a free radical (i.e., a molecule with an unpaired electron):

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#Unit 13. Methods in Biology

Photopolymerization is an alternative method that can be used to polymerize acrylamide gels. Ammonium persulfate and TEMED are replaced by riboflavin and when the gel is poured it is placed in front of a bright light for 2–3 h.

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#Unit 13. Methods in Biology

Photodecomposition of riboflavin generates a free radical that initiates polymerization.

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#Unit 13. Methods in Biology

Acrylamide gels can be made with a content of between 3% and 30% acrylamide Low concentration are used to where free movement of the proteins is required without any noticeable frictional effect such as flat-bed isoelectric focusing or the stacking gel system of an SDS–polyacrylamide gel.

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#Unit 13. Methods in Biology

Low-percentage acrylamide gels are also used to separate DNA. Gels of between 10 and 20% acrylamide are used in techniques such as SDS–gel electrophoresis, where the smaller pore size now introduces a sieving effect that contributes to the separation of proteins according to their size.