- Most abundant biological compounds.
- Sugars and starches make up a large part of the human diet.
- Each year photosynthetic processes in plants convert water and carbon dioxide into one hundred billion tons of carbohydrates.
- Exoskeletons of insects are made of carbohydrates.
- All carbohydrates have several of the –OH (hydroxy) groups common to alcohols.
- They also have the C=O (carbonyl) group of aldehydes and ketones.
- They are known as one or more polyhydroxy aldehyde or ketone
- Three main functions:
- energy storage
- an energy source for cellular functions
- glucose
- structural elements in plants and animals
- cellulose & chitin
- Classified into three groups based on the number of sugar units they contain.
- Monosaccharides
- Disaccharides
- Polysaccharides
Monosaccharides
- These are simple sugars. One polyhydroxy aldhyde or ketone.
- Rarely occur in nature by themselves.
- Usually bonded to an protein, fat or other carbohydrate.
- Glucose is the most abundant sugar in nature.
- The human body maintains a reasonably constant level of 80 to 120 mg of glu- cose per 100 mL of blood.
- Glucose is also the fundamental building block of the most common long-chain carbohydrates.
- Glucose in an aqueous solution exists in an equilibrium between the ring form and the straight-chain form.
- Fructose also forms ring structures when it is in solution.
- Since the carbonyl group is not at the end of the carbon chain, it forms a five-member ring.
Disaccharides
- Contain two monosaccharide units.
- An oxygen bridge between the two monosaccharides holds the two units together.
- Three disaccharides play an important part in the human diet—maltose, lactose, and sucrose.
- Maltose (glucose - glucose)
- germinating grain & digestion of starches
- Lactose (glucose - galactose)
- milk
- Sucrose (glucose - fructose)
- table sugar, fruits, sugar cane, beets, nectar
Polysaccharides
- Many sugar units, up to several million units
- Can be built with several different monosaccharide units
- Glycogen: energy storage
- Cellulose: gives plants structure
- Starch: supply nearly 3/4ths of the worlds food energy
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