Read through the following passage and then decide which words should be placed in the gaps.  
a  Enzymes are globular proteins which act as biological catalysts. They are able to temporarily bind with substrate molecules due to an region know as the active site. Because enzymes are proteins their activity can be affected by pH and temperature. The catalytic ability of enzymes depends on their three dimensional shape, this is more commonly refered to as the enzymes tertiary structure. During an enzyme catalysed reaction a transition occurs during which the reactants are referred to as the enzyme substrate complex.