B1 - Biological molecules

Question 1

Describe how the structure of glycogen is related to its function.

Answer 1

1. Helix/coiled/branched - so compact
   2.Polymer of glucose - so easily hydrolysed
2. Branched - so quickly hydrolysed
3. (polymer of ) Glucose - so provides respiratory substrate for energy
4. Insoluble - so does not effect water potential/osmosis

Question 2

Describe how the structure of starch and cellulose molecules are related to their functions.

Answer 2

Starch: (MAX 3)
1. Helix shape - so compatible
2. Insoluble - does not effect water potential/osmosis
3. Branched - so glucose released for respiration
4. Large molecule - cannot cross cell membrane

Cellulose: (MAX 3)
5. Long, straight/unbranched chains of B-glucose
6. Joined by hydrogen bonding
7. Crosslinkages form microfibrils
8. provides rigidity/ strength for plants

Question 3

Describe how the structures of a protein depends on the amino acids it contains.

Answer 3

1. Structure is determined by position of amino acid/ R group/ interactions
2. Primary structure is sequence/ order of amino acids
   3.Secondary structure formed by hydrogen bonding (A-helix/ B-pleated sheet)
3. Tertiary structure formed by interactions between R groups (hydrogen, ionic and disulphide)
4. Creates active site in enzymes OR complementary/specific shapes in antibodies/ carrier proteins/receptor
5. Quarternary structure sonatine 2 or more polypeptide chains

Question 4

Describe the structure of proteins.

Answer 4

1. Polymer of amino acids
2. Joined by peptide bonds
3. Formed by condensation reactions
4. Primary structure is order of amino acids
5. Secondary structure is folding of polypeptide chain due to hydrogen bonding (A-helix/ B-pleated sheets)
6. Tertiary structure is 3D folding due to hydrogen bonding and ionic/disulphide bonds
7. Quaternary structure is two or more polypeptide chains.

Question 5

Mucus produced by epithelial cells in the human gas exchange system contains triglycerides and phospholipids. Compare and contrast the structure and properties of triglycerides and phospholipids.

Answer 5

1. Both contain ester bonds (between glycerol and fatty acid)
2. Both contain glycerol
3. Fatty acids on both may be saturated or unsaturated
4. Both are insoluble in water
5. Both contain C and H and O but phospholipids also contain P, Triglycerides do not.
6. Triglyceride has 3 fatty acid and phospholipids have 2 fatty acids and a phosphate group
   7.Triglycerides are hydrophobic/ non-polar and phospholipids are hydrophilic and hydrophobic/ polar
7. phospholipids form bilayer in water but triglycerides do not.

Question 6

Mucus also contains glycoproteins. One of these glycoproteins is a polypeptide with the sugar, lactose attached. Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein.

Answer 6

1. Glucose and galactose
2. Joined by condensation reaction
3. Joined by glycosidic bonds
4. Added to polypeptide in Golgi apparatus

Question 7

In humans, the enzyme maltase breaks down maltose to glucose. This takes place at normal body temperature. Explain why maltase:
- only breaks down maltose
- allows this reaction to take place at normal body temperature

Answer 7

1. Tertiary structure of enzyme
2. Active site complementary to maltose/ substrate/ maltose fits into the enzyme’s active site
3. Description of induced fit;
4. Enzyme is a catalyst/ lowers activation energy/ energy required for reaction
5. By forming enzyme-substrate complex (binding stresses glycosidic bonds. between glucose molecules, so they are more easily broken)

Question 8

Scientists have investigated the effects of competitive and non-competitive inhibitors on the enzyme maltase. Describe competitive and non-competitive inhibition of an enzyme.

Answer 8

1. Inhibitors reduce binding of enzyme to substrate/ prevent ES complex formation

Competitive inhibition:
2. Inhibitor is a similar shape to substrate
3. Bind to active site
4. Inhibition can be overcome by increasing substrate concentration

Non-competitive inhibition:
5. Inhibitor binds to site on enzyme other than active site (allosteric site)
6. Prevents formation of active site/ changes shape of active site so induced fit model cannot work (substrate and active site are no longer complementary/similar
7. cannot be overcome by adding more substrate

Question 9

Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample.

Answer 9

Lipid:
1. Add ethanol then water and shake
2. White/ milky emulsion (if lipid is present)

Non-reducing sugar:
3. Do Benedict’s test and remains blue
4. Boil with acid then neutralise with alkali
5. Heat with Benedict’s reagent (if non-reducing sugar is present) turns red

Amylase:
6. Add buret and belies purple
7. Add starch, if present then test for reducing sugar (starch is A-glucose)