1 Introduction

Glucose is the fundamental fuel for cells of most living organisms. It is produced by plants and some prokaryotes through photosynthesis, wherein solar energy is absorbed, used to generate reducing equivalents (‘light reactions’) and then fix carbon dioxide as glucose (‘dark reactions’). Excess glucose is stored as polymeric forms, starch in plants and glycogen in animals. To utilize glucose as the source of energy, living organisms (from bacteria to humans) evolved glucose specific metabolic enzymes. Through processes, namely, aerobic respiration, anaerobic respiration or fermentation, cells use glucose to generate energy for production of other sugars, proteins, lipids, vitamins and nucleic acids that orchestrate the genesis, structure and function of all living systems. Proteins and lipids are also used by organisms not capable of photosynthesis to produce glucose through a process called gluconeogenesis. Under anaerobic and dark conditions, deep-sea bacteria developed chemosynthesis as alternative to photosynthesis. They use molecules such as carbon dioxide or methane as carbon source and inorganic molecules such as hydrogen gas, or hydrogen sulfide as a source of reducing equivalents to produce glucose. Commercially, glucose is manufactured through enzymatic hydrolysis of starch derived from crops.