Carbohydrates and Diabetes

Diabetes Complications

• High glucose levels in the blood can cause health problems over time if not managed properly
• Coma can result from both acidosis (due to ketone bodies production) and increased osmolality of extracellular fluid (mainly due to hyperglycemia and diuresis)

Carbohydrates

• Carbohydrates are the most abundant organic molecules in nature
• They have various functions, including providing dietary calories, acting as a storage form of energy, and serving as cell membrane components
• The empiric formula for simpler carbohydrates is (CH2O)n, hence the name "hydrate of carbon"
• Glucose is the most important carbohydrate

Classification of Carbohydrates

• Carbohydrates are classified as monosaccharides, disaccharides, oligosaccharides, or polysaccharides
• Monosaccharides cannot be hydrolyzed into simpler carbohydrates and are classified as trioses, tetroses, pentoses, hexoses, or heptoses
• Disaccharides are condensation products of two monosaccharide units (e.g. lactose, maltose, sucrose)
• Oligosaccharides are condensation products of three to ten monosaccharides (most are not digested by human enzymes)
• Polysaccharides are condensation products of more than ten monosaccharide units

Isomers and Epimers

• D and L isomerism: the orientation of the —H and —OH groups around the carbon atom adjacent to the terminal alcohol carbon determines whether the sugar belongs to the D or L series
• Most naturally occurring monosaccharides are D sugars, and the enzymes responsible for their metabolism are specific for this configuration
• Epimers: small differences in the structure of sugar molecules (e.g. glucose, mannose, and galactose)

Ring Structures of Monosaccharides

• Pyranose and furanose ring structures: similar to the ring structures of either pyran (six-membered ring) or furan (five-membered ring)
• Glucose in solution is mostly in the pyranose form (>99%)

Aldose-Ketose Isomerism

• Fructose and glucose have the same molecular formula (C6H12O6) but differ in the arrangement of atoms
• Glucose has an aldehyde group (at the end of the chain), while fructose has a ketone group (within the chain)
• This structural difference gives them distinct chemical and biological properties

Disaccharides

• α and β Maltose: two distinct forms of maltose, a disaccharide composed of two glucose molecules
• α Maltose: glycosidic bond between the two glucose molecules is formed with the alpha configuration
• β Maltose: glycosidic bond between the two glucose molecules is formed with the beta configuration
• Alpha maltose is the more common form found in nature and is the primary form produced during starch digestion

Polysaccharides

• Starch and glycogen are storage forms of glucose in plants and animals, respectively
• Amylose: a linear polymer of glucose units joined by alpha-1,4-glycosidic bonds
• Amylopectin: a branched polymer with both alpha-1,4 and alpha-1,6 glycosidic bonds

Glycoproteins

• Glycoproteins (also known as mucoproteins) are proteins containing branched or unbranched oligosaccharide chains including fucose
• They occur in cell membranes and many proteins are glycosylated
• Sialic acids (N- or O-acyl derivatives of neuraminic acid) are constituents of both glycoproteins and gangliosides