Biological molecules

1. List chemical elements which make up:

Carbohydrates 

• Carbon

• Hydrogen

• Oxygen

Fats

• Carbon

• Hydrogen

• Oxygen

Proteins

• Carbon 

• Hydrogen 

• Oxygen 

• Nitrogen 

2. State the main roles of carbohydrates, fats and proteins in living organisms 

Carbohydrates 

• Immediate source of energy

• Substrate for respiration, provide energy for cell activities

• Form supporting structures, eg. cell wall

• Converted into other organic compounds such as amino acids and fats

• Formation of nucleic acids, eg. DNA

• synthesise lubricants, eg. mucus which consists of a  carbohydrate and a protein 

• Synthesise the nectar in some flowers, a sweet liquid that attracts insects 

Fats

• insulation

• Long-term storage of energy

• Solvent for fat-soluble vitamins and many other vital substances such as hormones 

• Essential part of cells, especially in cell membranes

• Reduce water loss from skin surface, reducing rate of evaporation of water

Proteins

• Synthesis of new cytoplasm, growth and repair of worn-out body cells 

• Synthesis of enzymes and some hormones

• Formation of antibodies to combat diseases

3. Describe and carry out tests for:

Starch 

• Using iodine in potassium iodide solution 

Observations + conclusion 

• remained brown: absence of starch

• Turned from brown to blue-black: presence of starch

Reducing sugars

• using Benedict's solution

• Place in a boiling water-bath

Observations + conclusion 

• Remained blue: no reducing sugars

• Turned from blue to green: traces of reducing sugars

• Turned from blue to yellow or orange: moderate amount of reducing sugars

• Turned from blue to red/ red ppt. formed: large amount of reducing sugars

Protein

• Using biuret solution (CuSO4 + NaOH)

Observations + conclusion 

• remains blue: absence of proteins 

• turns from blue to violet: presence of proteins

Fats 

• using ethanol

Observations + conclusion 

• remained colourless: absence of fats

• White emulsion produces: presence of fats

4. State that large molecules are synthesised from smaller basic units

Carbohydrates 

• Cellulose, glycogen and starch form glucose

Proteins 

• polypeptides and proteins form amino acids

Fats

• lipids such as fats form glycerol and  fatty acids

5. Explain the modes of action of enzymes (how an enzyme speeds up a specific chemical reaction) in terms of active site, enzyme-substrate complex, lowering of activation energy and enzyme specificity using the ‘lock and key’ hypothesis 

• enzymes lowers the activation energy and speed up the chemical reaction 

• enzymes have a specific three-dimensional shape making it specific in action and only substrates with a shape complementary to the active site can bind with the enzyme

• Substrate binds to the active site of the enzyme forming an enzyme substrate complex

• While the substrate is attached to the active site, a chemical reaction occurs and the substrate is converted to the products

• The products will leave the active site

• Enzyme remains unchanged and can catalyse another reaction

6. Investigate and explain the effects of temperature and pH on the rate of enzyme catalyse reactions

Temperature 

Below optimum temperature,

• enzymes are less active

• Kinetic energy of molecules are low

• Enzyme and substrate molecules move slowly

• Decreased frequency of effective collisions between enzyme and substrate, lesser enzyme-substrate complex formed

Beyond optimum temperature,

• Active site of enzyme molecules begin to lose its original shape 

• No longer complementary to the shape of the substrate

• Denaturation occurs

pH

Below optimum pH,

• activity is low

Beyond optimum pH,

• enzymes denature