Describe structure & properties of alpha glucose & beta glucose.
Contains many polar hydroxyl(-OH) groups>readily forms hydrogen bonds in water, soluble
Contains free carbonyl(C=O) group>acts as reducing agent
What is the difference between alpha & beta glucose?
Alpha glucose - -OH group on C1 projected below plane of ring
Beta glucose - -OH group on C1 projected above plane of ring
Describe formation of a-1,4 glycosidic bond.
a-1,4 glycosidic bond is formed between the -OH group on C1 of an a-glucose monomer and the -OH group on C4 of another a-glucose monomer in a condensation reaction with the removal of 1 water molecule, catalysed by enzymes.
Describe breakage of a-1,4 glycosidic bond.
a-1,4 glycosidic bond between C1 of a a-glucose monomer and C4 of another a-glucose monomer is broken in a hydrolysis reaction with the addition of 1 water molecule, catalysed by maltase.
Describe structure of starch; amylose.
Amylose is an unbranched chain structure that consists of several hundred a-glucose residues linked by a-1,4 glycosidic bonds. Angle of these bonds causes amylose to coil helically. Most -OH groups are projected into the interior of the helix, hence there are no free -OH groups to form hydrogen bonds with water resulting in an insoluble molecule.
Describe test for reducing sugars.
Benedict's test
1. add 2cm3 of Benedict's solution to 2cm3 of sample in test tube.
2. put test tube in boiling water bath for 2 minutes.
results: blue->brick-red(increasing conc.)
Describe test for non-reducing sugars.
Acid hydrolysis
1. add 1cm3 of HCl(aq) to 2cm3 of sample in boiling tube. (hydrolyse gb)
2. place boiling tube in boiling water bath for 3 minutes.
3. add spatula of NaHCO3 powder to boiling tube. (neutralise soln)
Benedict's test
1. add 2cm3 of Benedict's solution to 2cm3 of sample in test tube.
2. put test tube in boiling water bath for 2 minutes.
Relate structure to function for starch; amylose.
Angle of a-1,4 glycosidic bonds causes amylose to coil helically into a more compact shape, allowing the packing of many glucose molecules per unit volume
-> large no. of glucose molecules, serves as good energy source in plants as glucose is oxidised to form ATP during respiration.
-> glycosidic bonds can be hydrolysed easily, releasing large no. of glucose to be oxidised - accessible source of glucose.
No free -OH groups to form hydrogen bonds with water forms an insoluble molecule
-> prevents its diffusion out of the cell & does not affect water potential in cell, suitable as energy storage molecule.
Describe structure of starch; amylopectin.
Amylopectin is a highly branched structure that contains a backbone of a-glucose residues linked by a-1,4 glycosidic bonds, with side chains formed by a-1,6 glycosidic bonds.
Relate structure to function for starch; amylopectin.
highly branched
-> many branched ends allow many hydrolytic enzymes to act on branched ends at any one time, amylopectin can be easily broken down into glucose to be used as respiratory substrates; accessible source of glucose.
glycosidic bonds
-> can be easily hydrolysed, releasing large number of glucose monomers to be used as respiratory substrates to be oxidised to produce large amount of ATP; accessible source of glucose.
Describe test for starch.
Presence of starch in solution turns orange iodine(I2/KI) solution to blue-black.
Describe structure of glycogen.
Glycogen is a highly branched structure that has a backbone of a-glucose residues held by a-1,4 glycosidic bonds, with side chains formed by a-1,6 glycosidic bonds. Side chains are shorter, more highly branched than amylopectin.
Relate structure to function; glycogen.
highly branched
-> many branched ends allow many hydrolytic enzymes to act on branched ends of glycogen at any one time, glycogen can be broken down into glucose to be used as respiratory substrates; accessible source of glucose.
backbone of a-glucose residues
-> packing of many glucose molecules per unit volume; serves as good energy source in animals as glucose is oxidised to produce ATP.
glycosidic bonds
-> can be easily hydrolysed to release a large number of glucose monomers, oxidised during respiration to form large amount of ATP
LARGE polysaccharide, makes it insoluble in water
-> prevents diffusion out of cell, glycogen won't change water potential in cell; good energy storage molecule.
Describe structure of cellulose.
A cellulose molecule consists of a long chain of b-glucose residues linked by b-1,4 glycosidic bonds, which makes the cellulose chain straight and unbranched. Successive b-glucose residues are rotated 180 degrees with respect to the adjacent residue, resulting in the -OH groups projecting outwards from each cellulose chain in all directions. Hydrogen bonds are formed between the -OH groups of neighbouring cellulose chains lying in parallel, resulting in cross-linking that binds the chains rigidly together. Cellulose chains bundle together to form microfibrils, which in turn bundle together to form macrofibrils which confers to high tensile strength, stability and support.
Relate structure to function; cellulose.
cellulose chains bundle together to form microfibrils, which in turn bundle to form macrofibrils which confer to high tensile strength, stability and support
-> main structural component of plant cell walls, high tensile strength of microfibrils prevents plant cell from lysing when water enters through osmosis.
-> when plant cell inflates with water, pressure develops inside cell and it becomes turgid; turgid cells support plants that lack wood.
large polysaccharide, most -OH groups form hydrogen bonds between cellulose chains, less -OH groups available to form hydrogen bonding with water; insoluble molecule.
-> won't change water potential of cell
macrofibrils arranged in several layers running in different directions forming cell wall
-> arrangement of fibres helps determine shape of plant cell as it grows
-> cell wall remains fully permeable to water, other solutes