 The ATP concentration inside the cell is typically 1 – 10 mM . ATP can be produced by redox reactions using simple and complex sugars ( carbohydrates ) or lipids as an energy source . For complex fuels to be synthesized into ATP , they first need to be broken down into smaller , more simple molecules . Carbohydrates are hydrolysed into simple sugars , such as glucose and fructose . Fats ( triglycerides ) are metabolised to give fatty acids and glycerol . 
