Re: What do EDTA and EGTA do, what are their differences, and their uses.

EDTA:

is an abbreviation of Ethylenediaminetetraacetic acid, which is also known as edetate, versene, or sequestrene. EDTA is, as you point out, a chelator, meaning that it binds to and makes unavailable metal ions in a solution. EDTA specifically chelates divalent cations (ions with a +2 charge), such as magnesium, manganese, zinc, and calcium (Mg⁺², Mn⁺², Zn⁺², and Ca⁺², respectively). Since these ions are essential for many enzymes to function, EDTA can be used to halt cellular activity, thus acting as a preservative. However, the cellular activities of one particular divalent cation, Ca⁺², go far beyond simply acting as a cofactor, and the relatively low affinity for Ca⁺², compared to Mg⁺² or Mn⁺², make EDTA a poor candidate for studying the effects and requirements of Ca⁺² on cells. So, researchers use:
EGTA:

or Ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-t etraacetic acid, which preferentially binds Ca⁺² with a significantly greater affinity than the other divalent cations, when they need to study Ca⁺². Thus, molecular geneticists studying DNA use a lot of EDTA - most DNA-cutting enzymes require Mg⁺² to function - while molecular physiologists studying nerves, muscles, or cell signaling use EGTA, which affects Ca⁺² currents without influencing other enzyme activities.