MONOSACCHARIDES – which formula? Molecular formula – C 6 H 12 O 6 or C 3 H 6 O 3 or C 5 H 10 O 5 Structural formula –
C 6 H 12 O 6 C 3 H 6 O 3 C 5 H 10 O 5 You decide! Triose or Pentose or Hexose
Pentose and hexose sugars exist in two forms: Straight chain forms Ring forms
Hydrogen Carbon Oxygen C6C6 H 12 O6O6
GLUCOSE comes in 2 forms, according how the ring closes. For example, this one: this H is above Here this H is above the carbon. This is called (alpha) glucose.
this H is below Here this H is below the carbon. This is called β (beta) glucose. WARNING! A single detail like this one makes all the difference. The position of the OH group on C1 will determine the type of polysaccharide it will form and in turn, the functions it will have in a cell.
Both these molecules are glucose. Both have a molecular formula of C 6 H 12 O 6. But they are structurally different and will have different functions in a cell. Structural Isomers
Biological role of monosaccharides As an energy source….. A large amount of energy is stored between the C-H bonds This is released to form ATP ATP is the energy currency of the cell As building blocks….. Repeated glucose molecules build up; starch & glycogen Ribose (5C) forms part RNA Deoxyribose (5C) forms part DNA
Forming a disaccharide… …MALTOSE 1.Two glucose molecules meet. 2.The OH from C1 & H from C4 react. 3.Water is expelled. This is called a condensation reaction. 4.The bond between the two joined glucoses is called glycosidic bond.
Polysaccharides Polymers with subunits of monosaccharides Repeated condensation reactions Normally thousands of monomers long Polysaccharides are not sugars STARCHCELLULOSEGLYCOGEN
Starch Polymer of glucose. Plant storage polysaccharide. Made up of two types of substances; 1)Amylose 2) Amylopectin Amylose Condensation reactions between α glucose (1-4 links). Forms from 1000s of condensation reactions. Coiled springs are formed.
Spiral structure of amylose; part of starch.
Amylopectin Condensation reactions between α glucose (1-4 links). Branches of 1-6 links also exist. Coiled springs with a branched structure are formed.
1-4 links form a helical structure 1-6 links form a branch structure
Amylopectin Mostly 1-4 links. Some 1-6 links.
Starch grains are a mixture of amylose & amylopectin Starch is a polysaccharide Starch it is a insoluble store of glucose Starch is only found in plant cells, the animal equivalent is called GLYCOGEN.
GLYCOGEN is the storage polysaccharide in animals It has 1-4 links and 1-6 links
Cellulose Present in plant cell walls. Has a slow decomposition. It is the most abundant organic molecule on the planet!! It is mechanically very strong. It is a polymer of β glucose
Cellulose C1-4 links make up this polysaccharide. If C1 and C4 are to react, one glucose molecule needs to flip through 180 o. It is this subtle difference that make cellulose so strong! This structure has H bonds holding the parallel chains together
70 chains of β glucose combine to form a MICROFIBRIL. Lots of MICROFIBRILS are held together to form FIBRES.