Elementary plant Biochemistry and Biotechnology (2+1)

Introduction

• Carbohydrates are major sources of energy for living organisms.
• The chief source of carbohydrate in human food is starch, which is the storage form of glucose in plants.
• Plants may store relatively large amounts of starch within their own cells in time of abundant supply, to be used later by the plant itself when there is a demand for energy production.
• Glycogen is the glucose storage polysaccharide of animals.
• It accounts for upto 10% of the mass of the liver and one percent of the mass of the muscle.
  
• Glycogen is larger and highly branched than amylopectin. By the action of several enzymes, such as α -amylase, α-amylase, amylo α(1→6) glucosidase and α(1→4) glucosidase, starch and glycogen from dietary intake are degraded finally to glucose.Carbohydrate is utilized by cells mainly in the form of glucose.
  
• The three principal monosaccharides resulting from the digestive processes are glucose, fructose and galactose. Both fructose and galactose are readily converted to glucose by the liver.
• Pentose sugars such as xylose, arabinose and ribose may be present in the diet, but their fate after absorption is obscure.
• Since glucose is the compound formed from starch and glycogen, the carbohydrate metabolism commences with this monosaccharide