Carbohydrates: Classification and Chemical Groups

• Carbohydrates is an essential molecule in the body, consisting of C, H, and O atoms.
• Carbohydrates are also called saccharides and include sugars, starch, and cellulose.
• Carbohydrates are divided into chemical groups based on increasing molecular weight (MW).

Carbohydrate Chemical Groups

• Monosaccharides consist of 1 unit, with names ending in "...ose".
• Disaccharides consist of 2 units, with names ending in "...ose".
• Polysaccharides consist of more than 2 units.

Classification of Carbohydrates

• Monosaccharides - Glucose, Fructose, Galactose
• Disaccharides - Maltose, Sucrose, Lactose
• Polysaccharides - Starch, Glycogen, Cellulose

Monosaccharides

• They are the simplest carbohydrates and cannot be broken down into smaller carbohydrates.
• The general chemical formula is (C•H₂O)n.
• Monosaccharides with three carbon atoms are called triose.
• Monosaccharides with four carbon atoms are called tetrose.
• Monosaccharides with five carbon atoms are called pentose.
• Functions as fuel molecules and building blocks for nucleic acids.
• Common examples include glucose and fructose.
• Link together to form polysaccharides.

Monosaccharides in Nature

• They are a major source of fuel for cellular metabolism.
• Glucose is the most important monosaccharide in nature.
• In plants, the equivalent to glycogen is stratch.
• In animals, glucose is stored in a space-efficient form called polysaccharide (glycogen, in humans and animals).
• Glycogen is stored in the liver and muscle cells.
• Fructose is found in fruit sugar, plants, and humans.
• Fructose is metabolized in the liver and absorbed directly into the intestines during digestion.

Disaccharides

• Formed when two monosaccharides join together, such as sucrose and lactose.
• They are composed of two monosaccharide units bound together by a covalent (glycosidic link) formed from a dehydration reaction (loss of H2O).
• There is a loss of a hydrogen atom from one monosaccharide and a hydroxyl group from the other when formed.
• Disaccharides have the chemical formula C12H22O11.

Disaccharides - Sucrose

• It is the most abundant disaccharide.
• Found in plants.
• Sucrose is composed of D-glucose and D-fructose.
• The bond between them is a glycosidic bond.

Disaccharides - Lactose

• It is composed of D-galactose and D-glucose.
• Sourced from Mammalian milk.
• Maltose is also another disaccharide.

Polysaccharides

• Polymeric long chains of monosaccharide units linked by glycosidic bonds.
• Can undergo hydrolysis to yield constituent monosaccharides.
• Can be linear or highly branched.
• They function in storage, such as starch and glycogen.
• They function in cellulose and chitin structure

Functions of Carbohydrates

• Polysaccharides store energy, such as starch and glycogen.
• Polysaccharides act as structural components in cells, such as cellulose in plants.
• Ribose, a 5-carbon monosaccharide, is important in genetic molecules (RNA and DNA).
• Saccharides are important for the immune system, fertilization, preventing disease, blood clotting, and foetal development.

Polysaccharides - Plants

• Starch is a polymer of glucose used as a storage molecule in plants.

Polysaccharides - Animals

• Glycogen is a more densely branched form of animal starch.
• Glycogen's properties allow it to be metabolized more quickly.
• Essential in the active lives of moving animals.

Classification of Carbohydrates

• Carbohydrates are classified as simple or complex.
• Simple carbohydrates (fructose) can raise blood glucose rapidly.
• Complex carbohydrates (starches) can raise blood sugar slowly.
• The Speed of digestion is determined by what else is consumed with the carbohydrate, how the food is prepared, inter-individual differences in metabolism, and the chemistry of the carbohydrate.

Carbohydrates and Nutrition

• Yield 3.87 calories of energy per gram of food, compared to fat at 9 calories per gram.
• Major metabolic pathways of monosaccharide catabolism are glycolysis and the citric acid cycle.
• In glycolysis, polysaccharides are cleaved into smaller monosaccharides by enzymes (glycoside hydrolase).
• Processed foods are associated with high levels of carbohydrates (sugars ie, biscuits).
• Unrefined foods have lower amounts of carbs and are associated with natural occurring foods ( i.e. vegetables).
• Dietary fiber (indigestible carbohydrates not changed), is not a source of energy.
• Dietary fiber functions to maintain a healthy digestive system.
• Inadequate fiber leads to significant increases in mortality, like bowel cancer.

Nutrition - Sugar

• Increased intake of sugar is associated with heart disease, type 2 diabetes, and some types of cancer.
• Natural sugars are not linked to health risks and also support fiber intake, vitamins, and minerals.
• Added sugars are the ones to limit.
• Reduced sugar intake is associated with improvements to weight and blood glucose levels.
• Food manufacturers and food labeling should support more informed choices for consumers.
• The recommended daily allowance (RDA) for adults is 30g of added sugar per day.

Glycolysis

• A metabolic pathway converts glucose (C6H12O6) into pyruvate (three carbon) (CH3COCOO− + H+).
• The energy released forms high-energy compounds: ATP and NADH.
• Glycolysis is a method that cells use to produce energy.
• It is carried out by 10 enzyme-based catalyzed reactions.
• Most monosaccharides (fructose and galactose) can be converted to one intermediate molecules.
• The intermediate molecules are used to form fatty acids.
• Fatty acids join to form fat.

Glycolysis location

• Occurs in most organisms in the cytosol (cytoplasm) of the cell.
• It is an oxygen-independent metabolic pathway.
• Does not use molecular oxygen which makes it an anaerobic process.
• Glycolysis is one of the most ancient metabolic pathways found in nature.
• The pathway is separated into two phases:
• The energy required phase, so called investment phase which consumes ATP.
• The energy releasing phase, in which ATP is produced.

Summary of Carbohdrates

• Different types (Classification) : Monosaccharides, disaccharides and polysaccharides.
• Roles and examples of each classification of carbohydrates.
• Simple vs complex carbohydrates
• Recommended daily allowance
• Benefits of a low sugar diet?
• Digestion of carbohydrates
• Process of Glycolysis

Explore the world of carbohydrates, essential molecules composed of C, H, and O atoms. Learn about their classification into monosaccharides, disaccharides, and polysaccharides based on molecular weight. Examples of each class are also provided.