Introduction to Carbohydrates

Study Notes

Carbohydrates are compounds containing carbon, hydrogen, and oxygen
The general formula for a carbohydrate is Cx(H₂O)y
They contain C=O and -OH functional groups
In plants, carbohydrates are produced via photosynthesis
The photosynthesis reaction is: 6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂
Cellular respiration equation is: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + energy
In humans, carbohydrates provide energy and carbon atoms for protein, lipids, and nucleic acid synthesis

Monosaccharides are simple sugars, not hydrolyzable into smaller units. Trioses, tetroses, pentoses, and hexoses are based on the number of carbon atoms
Disaccharides are made of two monosaccharides linked by a glycosidic bond
Oligosaccharides are chains of 2 to 10 sugar units
Polysaccharides are formed by the linkage of many monosaccharides
Carbohydrates are classified based on size of carbon chain, location of the CO functional group, number of sugar units, and stereochemistry of the compound

Carbohydrates provide energy to brain, erythrocytes, and retinal cells
Carbohydrates are stored primarily as liver and muscle glycogen
Carbohydrates provide carbon atoms for the synthesis of proteins, lipids, and nucleic acids
Carbohydrates are an important part of many food sources (sugars, flour, vegetable fiber)
They are important in the synthesis of nucleic acids, free nucleotides, and coenzymes
They are also important in hormones, receptors, and enzymes

Central carbons of carbohydrates are asymmetric (chiral), having four different groups attached
Stereoisomers are molecules with the same bonds but different spatial arrangements and properties
For each asymmetric carbon, there are 2ⁿ possible isomers. Example, there are two forms of glyceraldehyde

Glucose, fructose, and galactose are common monosaccharides
These sugars cannot be hydrolyzed into a simpler form
They contain 3-6 carbon atoms
Different configurations result in different stereoisomers. (D- or L- forms)
Absolute configuration of chiral Carbon furthest away from carbonyl group, determines whether D- or L-form of sugar

Based on the number of sugar units in the chain
Homopolysaccharides yield only one type of monosaccharide on hydrolysis (e.g., starch, glycogen, cellulose)
Heteropolysaccharides yield several types on hydrolysis
Amylose and amylopectin are starch and glycogen are branched carbohydrates
Cellulose is a linear structural polysaccharide

Dextran is a large polymer of glucose units with various linkages
Glycogen stores carbohydrates in animals (particularly in muscles and liver) - Structure is similar to amylopectin but more branched
Cellulose forms the skeleton of plant cells and does not occur in animals
Fibers are non-energy source in foods. Includes cellulose, hemicellulose, pectins, gums, lignins, cutins and tannins