Biochemicals

Carbohydrates are our body’s primary fuel source, and their metabolism is a vital process. It’s all about how we break down, build, and store these sugars to keep our energy levels stable

Key Metabolic Pathways:

• Core Concept: Carbohydrates are the body’s primary energy source, with glucose being the central player. Their metabolism is a carefully orchestrated series of pathways ensuring a constant energy supply and building blocks for other molecules

  • Glycolysis: The breakdown of glucose into pyruvate, yielding ATP and NADH. Occurs in the cytoplasm. The fate of pyruvate depends on oxygen availability (aerobic vs. anaerobic)
  • Gluconeogenesis: The synthesis of glucose from non-carbohydrate precursors (lactate, glycerol, amino acids). Primarily occurs in the liver during fasting. It helps to maintain blood glucose levels
  • Glycogenesis: The conversion of glucose to glycogen for storage, primarily in the liver and muscles. A way to store excess glucose
  • Glycogenolysis: The breakdown of glycogen to release glucose when needed
  • Pentose Phosphate Pathway (PPP): Produces NADPH (for reductive biosynthesis and antioxidant defense) and ribose-5-phosphate (for nucleotide synthesis)

• Regulation: These pathways are tightly regulated by hormones (insulin, glucagon, epinephrine, cortisol) and allosteric effectors (ATP, AMP, etc.) to maintain glucose homeostasis

Normal and Abnormal States

• Core Concept: Disruptions in carbohydrate metabolism lead to a range of diseases, most notably diabetes mellitus

  • Normal State: Normoglycemia

    • Fasting glucose: 70-99 mg/dL (3.9-5.5 mmol/L)
    • Postprandial glucose: <140 mg/dL (7.8 mmol/L)
    • Maintained by hormonal balance and efficient metabolic pathways

  • Abnormal States:

    • Hyperglycemia: Elevated blood glucose
      • Causes: Diabetes mellitus (Type 1, Type 2, gestational), other endocrine disorders, medications, stress
      • Complications: Acute (DKA, HHS) and chronic (retinopathy, nephropathy, neuropathy, cardiovascular disease)
    • Hypoglycemia: Low blood glucose
      • Causes: Excess insulin, liver disease, kidney disease, hormone deficiencies, alcohol consumption
      • Complications: Neurological symptoms, seizures, coma, brain damage
    • Insulin Resistance: Cells don’t respond properly to insulin
      • Consequences: Hyperinsulinemia, prediabetes, type 2 diabetes, metabolic syndrome
    • Genetic Disorders:
      • Glycogen Storage Diseases (GSDs): Enzyme deficiencies in glycogen metabolism
      • Galactosemia: Impaired galactose metabolism
      • Hereditary Fructose Intolerance: Impaired fructose metabolism
      • Pentosuria: Excess excretion of pentoses in the urine

Physical and Chemical Properties

• Core Concept: The structure of carbohydrates dictates their physical properties (solubility, taste) and chemical reactivity (oxidation, hydrolysis)

  • Monosaccharides:
    • Crystalline solids, water-soluble, sweet
    • Cyclization (anomers), oxidation (reducing sugars), esterification, glycoside formation
    • Examples: Glucose, fructose, galactose, ribose
  • Disaccharides:
    • Crystalline solids, water-soluble, sweet
    • Hydrolyzed by enzymes or acid
    • Can be reducing (lactose, maltose) or non-reducing (sucrose)
  • Polysaccharides:
    • Amorphous or fibrous, mostly insoluble, generally tasteless
    • Hydrolyzed by enzymes or acid
    • Vary in structure (linear vs. branched) and composition (homo- vs. heteropolysaccharides)
    • Examples: Starch, glycogen, cellulose