carbohydrates

• Carbohydrates


  Often referred to as saccharides (monosaccharides, disaccharides, oligosaccharides, polysaccharides)

  
• Carbohydrates


  • The major food source and energy supply for the body, stored primarily as liver and muscle glycogen
  • The name literally means carbon, hydrogen, and oxygen
  • General formula: Cx(H2O)y
  • All contain C=O (double bond) and -OH functional groups

  
• Classification of carbohydrates


  Based on: size of base carbon chain, location of carbonyl functional group, number of sugar units, stoichiometry of the compound

  
• Classification based on number of carbons

  • Trioses (3 carbons)
  • Tetroses (4 carbons)
  • Pentoses (5 carbons)
  • Hexoses (6 carbons)
  • Heptose (7 carbons)
  • Haptose (8 carbons)
  • Nonose (9 carbons)
• Aldose


  Carbohydrate with terminal carbonyl group

  
• Ketose


  Carbohydrate with ketone group in the middle

  
• Types of saccharides


  • Monosaccharides
  • Disaccharides
  • Oligosaccharides
  • Polysaccharides
• Monosaccharide


  Only have one sugar unit, simplest carbohydrates, cannot be further hydrolyzed
• Glycosides


  Monosaccharides linked by glycosidic linkage to form larger structures

  
• Disaccharides


  • Sucrose (glucose + fructose)
  • Maltose (2 glucose)
  • Lactose (glucose + galactose)

  
• Oligosaccharides


  1. 10 sugar units
• Polysaccharides


  • Homopolysaccharides (made of one monosaccharide)
  • Heteropolysaccharides (made of two or more monosaccharides)
• Homopolysaccharides


  • Starch (glucose)
  • Glycogen
• Heteropolysaccharides


  • Glycosaminoglycans

  
• Glucose


  Mostly tested to measure in laboratory, referred to as dextrose, used to assess total carbohydrate use by the body

  
• Fructose


  Referred to as fruit sugar, formed from glucose and breakdown of sucrose, intermediate in monosaccharide utilization
• Galactose


  Must be converted to glucose before it can be used by the body, less significant from a metabolic point of view
• Fischer projection


  Carbohydrate representation with open and cyclic forms
• Haworth projection


  Better representative of carbohydrate structure
• The only 2 types of carbohydrates which contribute to human nutrition are glucose and sucrose
• Glucose metabolism

  1. Glycolysis

  2. Krebs cycle

  3. Pentose phosphate pathway

  
• Glycolysis


  Breakdown or conversion of glucose to produce energy

  
• Gluconeogenesis


  Formation of glucose from non-carbohydrate sources

  
• Glycogenesis


  Creation and storage of glucose as glycogen
• Glycogenolysis


  Breakdown of glycogen to produce glucose

  
• Pancreas


  • Contains alpha, beta, and delta cells
  • Functions as both an endocrine and exocrine organ
  • Controls carbohydrate metabolism
• Insulin


  Considered the only hypoglycemic agent, responsible for entry of glucose into cells, synthesized by beta cells of pancreas, promotes glycogenesis and glycolysis, inhibits glycogenolysis
• Glucagon

  Considered the hyperglycemic agent, released during stress and fasting, synthesized by alpha cells of pancreas, promotes glycogenolysis and gluconeogenesis
• Other hormones that increase glucose concentration

  • Cortisol and corticosteroids (glucocorticoids)
  • Catecholamines
  • Growth hormone
  • Thyroid hormones
• Glycogenesis and glycolysis


  • Promoted by
• Lipogenesis


  • Promoted by
• Glycogenolysis


  • Inhibited by
• Glycolysis


  Breakdown of glucose into molecules

  
• Lipogenesis


  Conversion of glucose to glycogen, having formation of fatty acids

  
• Glycogenolysis


  Glycogen breakdown into glucose
• Glucagon


  • Considered as hyperglycemic agent
  • Released during stress and fasting state
  • Primary hormone responsible for increasing glucose levels
  • Synthesized by the alpha cells of the islets of Langerhans in the pancreas
  • Promotes glycogenolysis
  • Promotes gluconeogenesis
• Hormones that tend to increase glucose concentration

  • Cortisol and corticosteroids (glucocorticoids)
  • Catecholamines
  • Growth hormone
  • Thyroid hormones
  • Adrenocorticotropic hormone (ACTH)
  • Somatostatin
• Gluconeogenesis


  Cortisol, Thyroid hormones, ACTH
• Glycolysis


  Growth Hormone (GH) and Insulin
• Glycogenolysis


  • Glycogen to Glucose
  • Glucagon, Catecholamines, Growth Hormone (GH), Thyroid Hormones, ACTH