Carbohydrate Chemistry Overview

Carbohydrate Chemistry

• Carbohydrates are organic compounds made of C, H, and O.
• They generally have the formula (CH₂O)n, where the least number of n is 3.
• Carbohydrates are polyhydroxy-ketones or polyhydroxy-aldehydes.

Importance of Carbohydrates

• Main energy source
• Structural components in cell membranes
• Lubrication of joints and tendons (Proteoglycans)

Importance of CHO

• Pentose sugars are part of nucleotides, forming nucleic acids (DNA, RNA), coenzymes (NAD, FAD), regulatory molecules (cAMP, cGMP), and high-energy compounds (ATP, GTP).

Classification of Carbohydrates

• Classified according to the number of sugar units yielded on hydrolysis:
  • Monosaccharides: The simplest form, cannot be hydrolyzed further.
  • Oligosaccharides: Yields 2-10 monosaccharide units on hydrolysis.
  • Polysaccharides: Yields more than 10 monosaccharide units on hydrolysis.

Classification of Monosaccharides

• Classified by number of carbon atoms and active groups:
  • Trioses (3C): Aldo triose (e.g., glyceraldehyde), Keto triose (e.g., dihydroxyacetone)
  • Tetroses (4C): Aldo tetrose (e.g., erythrose), Keto tetrose (e.g., erythrulose)
  • Pentoses (5C): Aldo pentose (e.g., ribose), Keto pentose (e.g., ribulose)
  • Hexoses (6C): Aldo hexose (e.g., glucose, galactose), Keto hexose (e.g., fructose)
• Specific examples of monosaccharides:
  • Glucose: Essential energy source, blood sugar
  • Fructose: Sweetest, naturally in honey and fruits
  • Galactose: Rarely occurs as a single sugar

Oligosaccharides (Disaccharides)

• Type of carbohydrates formed of 2-10 monosaccharide units linked by glycosidic bonds.
• Examples:
  • Maltose: Malt sugar, formed of 2 glucose units
  • Sucrose: Cane sugar, formed of one glucose and one fructose unit
  • Lactose: Milk sugar, formed of one glucose and one galactose unit

Polysaccharides

• Classified as homogenous or heterogeneous.

• Homogenous Polysaccharides:

  • Starch: Major storage carbohydrate in plants, formed of amylose (long straight chains) and amylopectin (branched chains). Provides 80% of dietary calories globally.
  • Glycogen: Major storage carbohydrate in animals, mainly stored in liver and skeletal muscles. Highly branched structure for rapid glucose release (e.g., during exercise).
  • Cellulose: Major plant cell wall component; composed of long linear chains of glucose; non-digestible, increases stool bulk, prevents constipation.
  • Dextrin

• Heterogeneous Polysaccharides:

  • Glycolipids
  • Glycoproteins

Digestion and Absorption of Carbohydrates

• Digestion breaks down large molecules into their simplest form (monosaccharides).
• Mouth: Salivary amylase hydrolyzes starch into dextrins and maltose.
• Stomach: Amylase action stops due to low pH.
• Small Intestine: Pancreatic amylase converts starch and glycogen to disaccharides and monosaccharides. Disaccharidases (sucrase, lactase, maltase) further break down disaccharides to monosaccharides (glucose, fructose, and galactose).
• Absorption: Monosaccharides are absorbed into the bloodstream via glucose transporters (SGLT and GLUT).
• Large Intestine: Fibers attract water, soften stools, and ferment.
• Products of digestion: glucose, fructose, and galactose

Glucose in the Body

• Body stores glucose as glycogen in liver and muscle cells.
• Glucose is used for energy if glycogen is available.
• If glycogen stores are depleted, the body produces glucose from other sources.
• Blood glucose levels in healthy individuals after an overnight fast range from 70-100 mg/dL.

Regulation of Blood Glucose

• Insulin: Secreted by beta cells of the pancreas, moves glucose into cells, lowers blood sugar.
• Glucagon: Secreted by alpha cells of the pancreas, brings glucose out of storage, raises blood sugar.
• Epinephrine: Acts quickly to bring glucose out of storage during times of stress.

Abnormal Blood Glucose

• Hyperglycemia: High blood glucose, often associated with type 1 and type 2 diabetes.
• Type 1 Diabetes: Insulin deficiency; Less common
• Type 2 Diabetes: Insulin resistance; More common.
• Prediabetes: Higher-than-normal but not diagnostic of diabetes fasting blood glucose level from 100 to 125 mg/dL

Lactose Intolerance

• Inability to digest lactose (milk sugar)
• Symptoms include bloating, abdominal discomfort, and diarrhea.
• Causes: Lactase deficiency (natural decrease or damage to intestinal cells).

Lactose Intolerance Management

• Dietary changes: lactose-free diet initially, gradually increasing milk products, spreading dairy intake, using fermented dairy products (e.g., yogurt, acidophilus milk), using Lactase enzymes.

Recommended Intake of CHO

• RDA for carbohydrates is 130 g per day, or 45-65% of energy intake.

Artificial Sweetners

• Saccharin: Primarily for soft drinks and tabletop use.
• Aspartame: General purpose sweetener.

Explore the essence of carbohydrates, their chemical composition, and their vital roles in biological systems. This quiz covers their classification into monosaccharides, oligosaccharides, and polysaccharides, as well as their importance as energy sources and structural components. Test your understanding of carbohydrate chemistry concepts.