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