PEBC - Evaluating Examination

Quick important tips about Carbohydrates (Biochemistry)

Updated: 19/4/2017

So related to biochemistry we will review carbohydrates  for the EE, we will share the most important tips and notes related to the PEBC pharmacits evaluating exam!

Quick notes:

  • Carbohydrates are the main sources of energy in the body.
  • The liver has the major responsibility for maintaining blood glucose levels.
  • The brain oxidizes glucose to CO2 and H2O, whereas red blood cells oxidize glucose to pyruvate and lactate.
  • The digestion of carbohydrates occurs briefly in mouth and largely in the intestine.
  • Carbohydrates digestion begins in the mouth to a significant extent. During the process of mastication, salivary α-amylase (ptyalin) acts on starch randomly and cleaves α- 1,4-glycosidic bonds.
  • The enzyme salivary amylase is inactivated by high acidity (low pH) in the stomach. Therefore, the ongoing degradation of starch is stopped in stomach.
  • Non digestible carbohydrates : The fibers are chemically complex carbohydrates which include cellulose, hemicellulose, pectins, lignin and gums. ( Usually used as laxatives).

Classification:

  1. Monosaccharides : Glucose and Fructos.
  2. Disaccharides : two monosaccharides are combined together with elimination of a water molecule example: Sucrose, lactose, and maltose.
  3. Oligosaccharides : from two to ten monomers.
  4. Polysaccharides : More than 10 monomers as in cellulose and starch.

Metabolism of Carbohydrates:

Just to know what is the metabolism and the difference between anabolism and catabolism you can refer to this article : Metabolism ( Anabolism ↔ Catabolism )

So, metabolic pathway constitutes a series of enzymatic reactions to produce specific products.

Metabolism is divided into:

    • Anabolism : The biosynthetic reactions related to the formation of complex molecules from simple precursors or substrates.
    • Catabolism : The degradative processes related to the breakdown of complex molecules to simpler ones, with release of energy.

How do Carbohydrates metabolized ?

There are many pathways for Carbohydrates metabolism but we will go through the most important ones:

  1. Glycolysis (Embden-Meyerhof pathway) : The oxidation of glucose to pyruvate and lactate.
  2. Citric acid cycle (Krebs cycle or tricarboxylic acid cycle) : The oxidation of acetyl CoA to CO2. Krebs cycle is the final common oxidative pathway for carbohydrates, fats or amino acids, through acetyl CoA.
  3. Gluconeogenesis : The synthesis of glucose from non carbohydrate source & it is regulated by glucagon (e.g. amino acids, glycerol etc.).
  4. Glycogenesis : The formation of glycogen from glucose.
  5. Glycogenolysis : The breakdown of glycogen to glucose.
  6. Hexose monophosphate shunt (pentose phosphate pathway or direct oxidative pathway) : This pathway is an alternative to glycolysis and TCA cycle for the oxidation of glucose (directly to carbon dioxide and water).

Source : https://www.diapedia.org/5105287812/rev/16

Krebs cycle or tricarboxylic acid cycle:

  • The citric acid cycle (Krebs cycle or tricarboxylic acid—TCA cycle) is the most important metabolic pathway for the energy supply to the body.
  • Citric acid cycle essentially involves the oxidation of acetyl CoA to CO2 and H2O.
  • Krebs cycle is the most important central pathway connecting almost all the individual metabolic pathways.
  • The enzymes of TCA cycle are located in mitochondrial matrix, in close proximity to the electron transport chain. This enables the synthesis of ATP by oxidative phosphorylation without any hindrance.
  • The cycle operates only under aerobic conditions.

Source : https://biology.stackexchange.com/questions/23571/why-is-the-krebs-cycle-considered-a-part-of-aerobic-metabolism-if-molecular-oxyg

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