book 1 (biomolecule)

Question 1

differentiate between alpha and beta glucose molecules

Answer 1

• alpha glucose: it’s hydroxyl group on carbon atom 1 projects below the plane of the ring
• beta glucose: it’s hydroxyl group on carbon atom 1 projects above the plane of the ring

Question 2

describe the structure of starch

Answer 2

1. it consists of amylose and amylopectin, both made up of alpha glucose monomers
2. adjacent units not oriented 180 degrees to each other
3. amylose is unbranched and liked by alpha (1,4) glycosidic bonds. amylopectin is branched and linked by both alpha (1,4) glycosidic bonds as well as alpha (1,6) glycosidic bonds at branchpoints
4. both molecules have helical structure
5. absence of cross-linkages between different chains as hydroxyl groups points inwards

Question 3

describe the structure of glycogen

Answer 3

1. they are made up of alpha glucose monomers
2. the adjacent units are not oriented 180 degrees to each other
3. molecules are branched and linked by alpha (1,4) glycosidic bonds as well as alpha (1,6) glycosidic bonds at branchpoints
4. molecules are helical
5. the absence of cross-linkages formed between different chains in glycogen

Question 4

how does the structures of starch and glycogen relates to its function?

Answer 4

1. they are insoluble in water as they are large molecules and most of hydrophilic hydroxyl groups are projected into the interior of the helices - thus they are hydrophobic in nature and are insoluble in water - this is so that they can be stored in large quantities without greatly affecting the water potential of cells and are also prevented from diffusing out of the cells
2. they are compact in shape as the chains have helical structures and most of the hydroxyl groups or glucose are projecting into the interior of the helices so chains are not cross-linked to form bundles - the individual chains can fold into a very compact shape - thus can be stored in large quantities within the limited space in cells
3. they can be easily hydrolysed due to the presence of many branch-points and chains are not cross-linked to form big bundles - thus both starch and glycogen can be easily broken down by hydrolytic enzymes to glucose - the ease of breakdown allows glucose to be readily supplied for use in respiration eg

Question 5

describe the structures of cellulose

Answer 5

1. they are made up of beta-glucose monomers
2. the adjacent units are oriented 180 degrees to each other
3. molecules are unbranched and they are linked by beta (1,4) glycosidic bonds thus molecules are linear
4. presence of cross-linkages between parallel chains in cellulose as hydroxyl groups are projected outwards
5. the association of many cellulose molecules forms microfibrils and association of many microfibril forms macrofibrils

Question 6

how does the structure of cellulose relates to its function?

Answer 6

1. they have great tensile strength due to the 180 degree rotation of each glucose residues with respect to each other, there will be large numbers of hydroxyl groups project outwards from each cellulose molecule in all directions, thus forming many cross-linking between parallel chains to form microfibrils whereby the association of many microfibrils forms macrofibrils - thus cellulose has great tensile strength - prevents the plant cells from bursting when placed in solutions of higher water potential
2. they are insoluble in water as long chains of beta-glucose molecules and cross-linkages results in high molecular weight and crystalline structure, causing it to be insoluble in water and this is ideal to be the main building material for plants
3. there are large intermolecular spaces in between macrofibrils, causing it to be highly permeable and this allows for the passage of water and solute molecules through cellulose cell wall of plants cells.

Question 7

state the functions and properties triglycerides, relating it to the structures

Answer 7

1. functions as a good energy source as triglycerides have a higher number of hydrogen atoms per gram as compared to carbohydrates thus it can yield a greater amount of energy than carbohydrates per gram when oxidised during anaerobic respiration hence it is a compact energy store - this is useful for locomotion in animals whose body mass can be kept small, and useful in. being a long term energy storage in hibernating animals which require enough energy to be stored to last the winter