Biomolecules

Question 1

Formation of a-1,4 glycosidic bonds

Answer 1

1. a-1,4 glycosidic bond is formed between carbon 1 of an a-glucose monomer and carbon 4 of another a-glucose monomer
2. via condensation reaction
3. catalysed by enzymes

Question 2

Breaking of a-1,4 glycosidic bonds

Answer 2

1. a-glycosidic bond is broken between carbon 1 of an a-glucose monomer and carbon 4 of another a-glucose monomer
2. via hydrolysis reaction
3. catalysed by maltase

Question 3

Structure and roles of Amylose

Answer 3

1. Unbranched chain structure of a-glucose residues linked by a-1,4 glycosidic bonds
2. The angle of these bonds causes the chain to coil helically into a more compact shape, allowing the packing of many glucose molecules per unit volume
3. Due to the large number of glucose molecules, amylose serves as a good energy source in plants as glucose is oxidised during respiration to produce ATP
4. Most of the -OH groups are projected towards the interior of the amylose helix
5. Insoluble nature of amylose prevents its diffusion out of the cell, so water potential within the cell does not change, hence, serving as a suitable energy storage molecule

Question 4

Structure and roles of amylopectin

Answer 4

1. Backbone of a-glucose residues linked by a-1,4 glycosidic bonds
2. Highly branched with side chains formed by a-1,6 glycosidic bonds
3. These highly branched ends allows many hydrolytic enzymes to act on these branched ends at any one time, allowing amylopectin to be easily broken down into its glucose monomers to be used as respiratory substrates. Hence, serving as an accessible source of glucose

Question 5

Structure and roles of cellulose

Answer 5

1. Unbranched chain structure of b-glucose residues linked by b-1,4 glycosidic bonds
2. Each b-glucose residue is rotated 180 degrees with respect to its adjacent residue
3. This successive rotation results in -OH groups projected outwards from each cellulose chain in all directions
4. Hydrogen bonds are formed between -OH groups of neighbouring cellulose chains lying in parallel, resulting in cross linking, binding the cellulose chains rigidly together.
5. Cellulose chains associate to form microfibrils and in turn macrofibrils, conferring high tensile strength to cellulose, preventing lysis of the plant cell when water enters the cell by osmosis

Question 6

Structure and roles of glycogen

Answer 6

1. Backbone of a-glucose residues linked by a-1,4 glycosidic bonds
2. Highly branched with side chains formed by a-1,6 glycosidic bonds.
3. These highly branched ends allows many hydrolytic enzymes to act on these branched ends at any one time, allowing glycogen to be easily broken down into its glucose monomers to be used as respiratory substrates. Hence, glycogen serves as an accessible source of glucose in animals

Question 7

Formation of ester bonds

Answer 7

1. Forms between -OH group of glycerol and -COOH group of fatty acid
2. via condensation reaction
3. catalysed by enzymes

Question 8

Breaking of ester bonds

Answer 8

1. Breaks between -OH group of glycerol and -COOH group of fatty acid
2. via hydrolysis
3. catalysed by enzymes

Question 9

Triglycerides

Answer 9

Good energy source:
- Higher ratio of energy storing C-H bonds than carbon atoms, compared to carbohydrates
- More than twice the amount of energy, in the form of ATP, is released from the oxidation of a given mass of triglycerides compared to an equal mass of carbohydrates

Good energy storage:
- Contains more energy per gram than carbohydrates, providing the most weight efficient means for plants and animals to store energy
- Triglycerides are large and non-polar, preventing its diffusion out of the cell, hence, water potential within the cell does not change. Thus, serving as a good energy storage molecule

Source of metabolic water:
- High proportion of hydrogen and an almost insignificant proportion of oxygen in triglycerides compared to carbohydrates
- During aerobic respiration, complete oxidation of triglycerides produces a larger amt of metabolic water per gram of triglyceride compared to the oxidation of an equal mass of carbohydrates.

Question 10

How does structure of collagen differ from structure of starch

Answer 10

1. Collagen made up of amino acids while starch made up of a-glucose
2. Collagen linked by peptide bonds while starch linked by a-1,4 glycosidic and a-1,6 glycosidic bonds
3. Collagen has 3 helical polypeptides winded tightly around each other to form a tropocollagen while amylose is helical and amylopectin is highly branched
4. Collagen unbranced while starch branched

Question 11

Similarities between structure of collagen and cellulose

Answer 11

1. Both are unbranched structures
2. Both insoluble in water
3. Both serves a structural function, conferring high tensile strength
4. Both are polymers
5. Both contains cross-linking between polypeptide chains