Biological Molecules

Question 1

What are the key molecules required for life?

Answer 1

Carbohydrates, Proteins, Lipids, Nucleic Acids, and Water.

Question 2

Define monomers and polymers.

Answer 2

Monomers: Smaller units that join together to form larger molecules.
Polymers: Large molecules made of repeating monomer units.

Question 3

What makes carbon essential to biological molecules?

Answer 3

Carbon can form four covalent bonds, making stable structures.
It bonds with elements like hydrogen, oxygen, nitrogen, and sulfur to form diverse molecules.
Carbon chains can be straight, branched, or cyclic, enabling structural variety.

Question 4

What are carbohydrates?

Answer 4

Organic compounds containing carbon (C), hydrogen (H), and oxygen (O) in a Cx(H2O)y ratio.

Question 5

Name the three types of carbohydrates and describe their roles.

Answer 5

Monosaccharides: Single sugar units (e.g., glucose).
Disaccharides: Two monosaccharides joined by a glycosidic bond (e.g., sucrose).
Polysaccharides: Long chains of monosaccharides, used for storage or structure (e.g., starch, glycogen, cellulose).

Question 6

What are monosaccharides, and how are they classified?

Answer 6

Single sugar units classified based on the number of carbon atoms:
- Glucose
- Galactose
- Fructose

Question 7

Explain the two isomers of glucose.

Answer 7

Alpha (𝛼)
α) glucose: The -OH group on carbon 1 is below the plane of the ring.
Beta (𝛽)
β) glucose: The -OH group on carbon 1 is above the plane of the ring.

Question 8

How are reducing and non-reducing sugars different?

Answer 8

Reducing sugars: Can donate electrons, reducing copper sulphate to form a brick-red precipitate in Benedict’s test (e.g., glucose, galactose).

Non-reducing sugars: Cannot donate electrons; must be hydrolysed to monosaccharides before testing (e.g., sucrose).

Question 9

How are disaccharides formed, and what bond is involved?

Answer 9

Formed by condensation reactions between two monosaccharides, creating a glycosidic bond and releasing a water molecule.

Question 10

Give examples of disaccharides and their monomers.

Answer 10

Maltose: Two
α-glucose molecules.

Sucrose:
α-glucose + fructose.

Lactose:
α-glucose + galactose.

Question 11

How can you calculate the formula of a disaccharide?

Answer 11

Add the monomers’ formulas and subtract one water molecule (H20)

Question 12

What are polysaccharides, and how are they classified?

Answer 12

Polymers of monosaccharides joined by glycosidic bonds:
Storage polysaccharides: E.g., Starch (plants), Glycogen (animals).

Structural polysaccharides: E.g., Cellulose (plant cell walls).

Question 13

What are the components of starch?

Answer 13

Amylose: Unbranched, helical chain with
1,4 glycosidic bonds.

Amylopectin: Branched chain with 1,4 and
1,6 glycosidic bonds, allowing rapid energy release.

Question 14

Why is starch an effective storage molecule?

Answer 14

Compact structure for storage.
Insoluble, preventing osmotic effects in cells.

Question 15

What makes glycogen suitable for energy storage?

Answer 15

Highly branched structure allows rapid hydrolysis for glucose release, essential for animals’ high energy demands.

Question 16

What gives cellulose its strength?

Answer 16

Long chains of
β-glucose with 180° rotation between molecules.
Extensive hydrogen bonding between chains, forming microfibrils.

Question 17

What happens in condensation and hydrolysis reactions?

Answer 17

Condensation: Forms glycosidic bonds, removing water.

Hydrolysis: Breaks glycosidic bonds by adding water.

Question 18

Give examples of biological processes involving these reactions.

Answer 18

Condensation: Formation of starch and glycogen.

Hydrolysis: Digestion of carbohydrates into monosaccharides.

Question 19

How do you test for reducing sugars?

Answer 19

Add Benedict’s reagent and heat. A colour change from blue to brick-red indicates the presence of reducing sugars.

Question 20

How do you test for non-reducing sugars?

Answer 20

Hydrolyse with dilute hydrochloric acid.
Neutralize with sodium hydrogen carbonate.
Perform Benedict’s test.

Question 21

How is starch detected?

Answer 21

Add iodine in potassium iodide solution. A blue-black colour indicates starch.

Question 22

What is chromatography used for in biology?

Answer 22

To separate mixtures (e.g., monosaccharides) based on their solubility in a mobile phase.

Question 23

How is paper chromatography performed?

Answer 23

Place the sample on chromatography paper.
Suspend it in a solvent.
Analyse the distances travelled by components.

Question 24

How can Benedict’s solution estimate glucose concentration?

Answer 24

Prepare standard glucose solutions using serial dilutions.
Compare the color change of unknown samples to these standards.
Use a colorimeter for precise absorbance measurements.

Question 25

What are lipids, and what elements do they contain?

Answer 25

Lipids are macromolecules containing carbon, hydrogen, and oxygen, with a lower proportion of oxygen than carbohydrates. They are non-polar and hydrophobic (insoluble in water).

Question 26

What are the two main types of lipids?

Answer 26

Triglycerides and Phospholipids.

Question 27

What are the monomers of triglycerides?

Answer 27

Glycerol (an alcohol with hydroxyl groups) and fatty acids.

Question 28

Describe the structure of fatty acids.

Answer 28

Contains a methyl group (-CH₃) at one end and a carboxyl group (-COOH) at the other.
The hydrocarbon chain (R group) is 4-24 carbons long.
Fatty acids are either saturated or unsaturated.

Question 29

What is the difference between saturated and unsaturated fatty acids?

Answer 29

Saturated: No double bonds, straight chains, solid at room temperature (e.g., animal fats).
Unsaturated: One or more double bonds causing kinks, liquid at room temperature (e.g., vegetable oils).