Function of carbohydrates
- building blocks for larger molecules
- energy storage — starch (plant) and glycogen (animal)
- structural — cellulose cell wall (plant) and chitin (insects, crabs, shrimps)
The bond between monomers of carbohydrates is known as glycosidic bond.
Monosaccharides
- monomers of carbohydrates
- eg. glucose, fructose, galactose
- all monosaccharides are reducing sugars
Disaccharides
- made up of two monosaccharides
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- made up of many monosaccharides
- polymer of glucose molecules
- has two components; amylose and amylopectin
- both fit together to form a complex 3-dimensional structure which is insoluble in water
- amylose helices are entangled in the branches of amylopectin molecules
- each amylose chain is coiled into a helix, with six glucose residues for every complete turn of the helix — compact shape making it a complex structure for storage
- amylopectin have many branches
What is glycogen?
- animal equivalent of starch
- found in liver and skeletal muscles of vertebrate animals
Starch and glycogen (energy stores)
- their molecules have many side branches where glucose molecules can be removed from their tips (by enzymes)
- their insolubility stops them interfering with osmosis
- their compactness provides an efficient way to store lots of glucose for future cellular respiration
Cellulose (long, unbranched chain)
- most abundant organic molecule on Earth
- major component of cell wall in plants
- made from long, straight unbranched chains of glucose
- chains cross-linked by H-bonds which holds them tightly together (excludes water)
- chemically very inert and insoluble
- many molecules form strong fibrils
- only some bacteria, fungi and a very small number of animals can secrete cellulase enzymes
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