Chap no. 5- An Introduction to Carbohydrates
Carbohydrates: the term refers to monomers called monosaccharides, small polymers called
oligosaccharides and large polymers called polysaccharides.
● The chemical formula of carbohydrates/sugars is ❑ , n refers to no. of carbon-
● These molecules consist of carbonyl group and several hydroxyl groups (-OH).
5.1 Sugars as monomers
● Sugars provide chemical energy in cells and act as building blocks for more complex
● Monosaccharides differ from each other in three ways:
○ position of carbonyl group
○ no. of carbon atoms
○ different arrangement of hydroxyl groups and alternative ring forms.
● The presence of carbonyl group along with multiple hydroxyl groups provides an array of
functional groups in sugars.
● Ribose- acts as building blocks for nucleotides, 5 carbons
● Pentose- the glucose that is coursing through our bloodstream
● Hexose- 6 carbon sugar used by body cells
● Each monosaccharide has a unique structure and function
Structure of monosaccharides:
● sugars normally form rings, not linear chains in aqueous solutions.
● carbon-1 in linear chain forms bond with oxygen and hydroxyl group.
● new hydroxyl group on C-1 either below or above plane of the ring.
5.2 Structure of Polysaccharides:
● Polysaccharides- polymers that form when monosaccharides are linked together.
● Disaccharides-simples polysaccharides consisting of two sugars
● Glycosidic linkages- simple sugars polymerize when a condensation reaction occurs
between two hydroxyl groups resulting in a covalent bond.
● the location of geometry of glycosidic linkages can vary widely among polysaccharides
due to the presence of different (-OH) groups.
Structure of Starch: energy storage in plants
● glucose monomers joined by glycosidic linkages
● the angle b/w C-1 &C-4 causes the coiling into helix
● a mixture of two polysaccharides:
● branching occurs (every 30 monomers)when glycosidic linkages form b/w C1 from one
strand and C6 on another
Structure of glycogen: energy storage in animals
● animals-store sugar/glycogen in liver, muscles.
● nearly identical to starch except many more branches (every 10 monomers)
● when exercising enzymes break glycogen into glucose
Structure of cellulose: structural function in plants
● Cellulose- a major component of plant cell wall, very strong
● polymer of glucose monomers linked by linkages
● adjacent monomers flipped: allows parallel strands to be hydrogen bonded and generates linear molecules
Structure of Chitin:
● Chitin-stiffens cell walls of fungi, important component of external skeletons of insects
● polymer of N-acetylglucosamine monomers