Carbohydrates Summary

Biological Molecules: Carbohydrates

Structure and Functions of Carbohydrates (CHO's)

  • Monosaccharides
  • Disaccharides
  • Polysaccharides
  • Key CHO’s in the human diet
  • Digestion of CHO’s

Biological Organic Molecules

  • Carbohydrates
  • Lipids
  • Proteins
  • Nucleic acids

Introduction to Carbohydrates

  • Carbohydrates are the most abundant of the organic compounds.
  • Source of most carbohydrates is plants.
  • Photosynthesis produces glucose which can be converted into other carbon compounds in the plant.
  • Glucose: C6H{12}O_6

Types of Carbohydrates

  • Monosaccharides: Simple sugars (e.g., glucose)
  • Disaccharides: 2 simple sugars paired up (e.g., sucrose)
  • Polysaccharides: Complex sugars (e.g., starch)
  • Monosaccharides do NOT require digestion prior to absorption from the gut.

Monosaccharides

  • One-unit sugars (simple sugars)
  • Building blocks of more complex sugars and starches
  • Pentose sugars (5 carbons): ribose, deoxyribose
  • Hexose sugars (6 carbons): glucose, fructose, galactose

Disaccharides: Two-Unit Sugars

  • Sucrose: glucose + fructose
  • Lactose: glucose + galactose
  • Maltose: glucose + glucose
  • Disaccharides must be digested by enzymes, forming monosaccharides, before they can be absorbed.

Polysaccharides: Many Units of Glucose

  • Starch: Energy storage carbohydrate in plants; chains vary in length (100’s to 100,000’s of glucose units).
  • Glycogen: Made by animals to store glucose; stored in muscle and liver.
  • Cellulose: Fibre made by plants for structural support; humans can't digest it; necessary as roughage/fibre in the digestive tract.

Digestion of Starch

  • Starch is the only polysaccharide digested by humans.
  • Digestion of starch produces glucose for the body’s cells.
  • Step 1: starch + amylase \rightarrow maltose
  • Step 2: maltose + maltase \rightarrow glucose

Glucose Oxidation in Cells (Aerobic Cell Respiration)

  • C6H{12}O6 + 6 O2 \rightarrow 6 CO2 + 6 H2O + energy released
  • Cell respiration is the biochemical pathway animals, plants and most bacteria use to convert food molecules to energy for cellular work.
  • Reactions that release energy are EXOTHERMIC.
  • The process is aerobic because it requires oxygen.
  • Cell respiration is the opposite process to photosynthesis.
  • Cellular energy is often referred to as ATP