2.5 Enzymes
Essential idea: Enzymes control the metabolism of the cell.
Nature of science: Experimental design—accurate, quantitative measurements in enzyme experiments require replicates to ensure reliability. (3.2)
Understandings:
• Enzymes have an active site to which specific substrates bind.
• Enzyme catalysis involves molecular motion and the collision of substrates with the active site.
• Temperature, pH and substrate concentration affect the rate of activity of enzymes.
• Enzymes can be denatured.
• Immobilized enzymes are widely used in industry.
Theory of knowledge:
• Development of some techniques benefits particular human populations more than others. For example, the development of lactose-free milk available in Europe and North America would have greater benefit in Africa/ Asia where lactose intolerance is more prevalent. The development of techniques requires financial investment. Should knowledge be shared when techniques developed in one part of the world are more applicable in another?
Application and Skills:
• Application: Methods of production of lactose-free milk and its advantages.
• Skill: Design of experiments to test the effect of temperature, pH and substrate concentration on the activity of enzymes.
• Skill: Experimental investigation of a factor affecting enzyme activity. (Practical 3)
Utilization:
• Enzymes are extensively used in industry for the production of items from fruit juice to washing powder.
Guidance:
• Lactase can be immobilized in alginate beads and experiments can then be carried out in which the lactose in milk is hydrolysed.
• Students should be able to sketch graphs to show the expected effects of temperature, pH and substrate concentration on the activity of enzymes. They should be able to explain the patterns or trends apparent in these graphs.
2.4 Proteins
Essential idea: Proteins have a very wide range of functions in living organisms.
Nature of science: Looking for patterns, trends and discrepancies—most but not all organisms assemble proteins from the same amino acids. (3.1)
Understandings:
• Amino acids are linked together by condensation to form polypeptides.
• There are 20 different amino acids in polypeptides synthesized on ribosomes.
• Amino acids can be linked together in any sequence giving a huge range of possible polypeptides.
• The amino acid sequence of polypeptides is coded for by genes.
• A protein may consist of a single polypeptide or more than one polypeptide linked together.
• The amino acid sequence determines the three-dimensional conformation of a protein.
• Living organisms synthesize many different proteins with a wide range of functions.
• Every individual has a unique proteome.
Applications and skills:
• Application: Rubisco, insulin, immunoglobulins, rhodopsin, collagen and spider silk as examples of the range of protein functions.
• Application: Denaturation of proteins by heat or by deviation of pH from the optimum.
• Skill: Drawing molecular diagrams to show the formation of a peptide bond.
Utilization:
• Proteomics and the production of proteins by cells cultured in fermenters offer many opportunities for the food, pharmaceutical and other industries.
Aims:
• Aim 7: ICT can be used for molecular visualization of the structure of proteins.
• Aim 8: Obtaining samples of human blood for immunological, pharmaceutical and anthropological studies is an international endeavour with many ethical issues.
Guidance:
• The detailed structure of the six proteins selected to illustrate the functions of proteins is not needed.
• Egg white or albumin solutions can be used in denaturation experiments.
• Students should know that most organisms use the same 20 amino acids in the same genetic code although there are some exceptions. Specific examples could be used for illustration.