44
Introduction
Metabolism is the net result of all the biochemical processes occurring in living
organisms that involve the conversion of food into smaller particles and the production of energy which is required for the structural and functional purposes vital to
sustaining life [1]. Metabolic processes may be catabolism which refers to the degradation of macromolecules to yield simpler ones with the production of energy [2]
or anabolism which refers to the biosynthesis of macromolecules by consuming
energy, e.g., lipids, proteins, DNA, RNA, etc. [3]. Every metabolic pathway is
dependent on some specific enzymes and certain substrates for its smooth functioning [4].
Metabolic disorders can be defined as inborn errors of metabolism caused by
deficiencies of certain enzymes that are involved in the metabolism of proteins,
lipids, or carbohydrates. The enzyme deficiency is because of the inherited gene
mutations for the respective enzyme [5]. More than 600 genetic metabolic disorders
have been identified so far and all presenting different signs and symptoms, many of
them are present in newborns and maybe within a short time after birth [6]. Such
metabolic disorders are referred to as inborn errors of metabolism (IEM). Genetic
deficiency of catalytic enzymes in the metabolic pathways is the main reason for
IEM, but cellular process abnormalities which involve cell signaling, transmembrane transport, cell differentiation, and production of energy also contribute a lot
[1]. Such disorders are although rare, but collectively they can lead to childhood
disability and deaths. Many of them are autosomal recessive disorders [7].
Carbohydrate, being the essential component of our diet, provides almost 50% of
energy from total dietary energy intake. Endogenous reserves in the body such as
liver glycogen and muscles are also the sources of carbohydrates. The dietary carbohydrates comprised monosaccharide as fructose, glucose, and galactose, disaccharides as sucrose, maltose, and lactose, and polysaccharides as starch, among
these the starch and sucrose constitute the major portion of dietary carbohydrates
[8]. Carbohydrate metabolism involves the digestion of dietary carbohydrates in the
gastrointestinal tract and results in the breakdown of complex molecules into monosaccharides which is then transferred to the cells via glycolysis, pentose phosphate
pathway, and Krebs cycle for aerobic and anaerobic respiration. Figure 2.1 is a schematic representation of all biochemical pathways happening in cytoplasm and mitochondria [9].
Metabolism of carbohydrates provides elements for nucleic acids which constitutes its functional role and also provides a major source of energy. Impaired carbohydrate metabolism occurs due to the disruption in the metabolic pathway of
carbohydrates which results in metabolic disorders [10]. The disorders of carbohydrate metabolism can be categorized as follows.
H. Sharif et al.
Introduction
Metabolism is the net result of all the biochemical processes occurring in living
organisms that involve the conversion of food into smaller particles and the production of energy which is required for the structural and functional purposes vital to
sustaining life [1]. Metabolic processes may be catabolism which refers to the degradation of macromolecules to yield simpler ones with the production of energy [2]
or anabolism which refers to the biosynthesis of macromolecules by consuming
energy, e.g., lipids, proteins, DNA, RNA, etc. [3]. Every metabolic pathway is
dependent on some specific enzymes and certain substrates for its smooth functioning [4].
Metabolic disorders can be defined as inborn errors of metabolism caused by
deficiencies of certain enzymes that are involved in the metabolism of proteins,
lipids, or carbohydrates. The enzyme deficiency is because of the inherited gene
mutations for the respective enzyme [5]. More than 600 genetic metabolic disorders
have been identified so far and all presenting different signs and symptoms, many of
them are present in newborns and maybe within a short time after birth [6]. Such
metabolic disorders are referred to as inborn errors of metabolism (IEM). Genetic
deficiency of catalytic enzymes in the metabolic pathways is the main reason for
IEM, but cellular process abnormalities which involve cell signaling, transmembrane transport, cell differentiation, and production of energy also contribute a lot
[1]. Such disorders are although rare, but collectively they can lead to childhood
disability and deaths. Many of them are autosomal recessive disorders [7].
Carbohydrate, being the essential component of our diet, provides almost 50% of
energy from total dietary energy intake. Endogenous reserves in the body such as
liver glycogen and muscles are also the sources of carbohydrates. The dietary carbohydrates comprised monosaccharide as fructose, glucose, and galactose, disaccharides as sucrose, maltose, and lactose, and polysaccharides as starch, among
these the starch and sucrose constitute the major portion of dietary carbohydrates
[8]. Carbohydrate metabolism involves the digestion of dietary carbohydrates in the
gastrointestinal tract and results in the breakdown of complex molecules into monosaccharides which is then transferred to the cells via glycolysis, pentose phosphate
pathway, and Krebs cycle for aerobic and anaerobic respiration. Figure 2.1 is a schematic representation of all biochemical pathways happening in cytoplasm and mitochondria [9].
Metabolism of carbohydrates provides elements for nucleic acids which constitutes its functional role and also provides a major source of energy. Impaired carbohydrate metabolism occurs due to the disruption in the metabolic pathway of
carbohydrates which results in metabolic disorders [10]. The disorders of carbohydrate metabolism can be categorized as follows.
H. Sharif et al.