- The reaction rate increases as the substrate concentration increases, until the maximum rate of reaction is achieved. The rate of reaction then reaches a plateau, and increases no further.
- The reaction rate is limited at low concentrations by the availability of substrate, while at high concentrations, the rate is limited by the availability of enzyme active sites.
8.2 Applications and skills
8.2.1 Enzyme inhibition and rates of reaction
- Metabolic pathways can be manipulated for different purposes. One way to alter a is to introduce an inhibitor. Another way is to continuously extracting product to encourage overdevelopment of a specific metabolite.
- Many pharmaceuticals, including antibiotics, work by altering the s in disease-causing organisms. Bioinformatics makes it easier to determine which enzymes to target.
Application: Use of databases to identify potential new anti-l drugs
- Malaria is caused by a number of species of micro-organism of the genus Plasmodium, especially Plasmodium falciparum. These protozoans live as sporozoites in the gut of the female Anopheles mosquito, and are transmitted via bites to a human host. The parasite then develops, rupturing hepatocytes and infecting erythrocytes, and causing weakness, chills, fever, vomiting and seizures.
- In 2002, a complete genome for Plasmodium falciparum strain 3D7 was sequenced. The existence of the database can help researchers locate enzymes that could be inhibited in anti-malarial drugs.
- They could also test different drugs on mutant strains of Plasmodium and determine, using the database, which genes are associated with altered responses to the drugs. This type of research is called chemogenomics.
Skill: Distinguishing different types of inhibition from graphs at specified substrate concentration.
- Both inhibitor A and inhibitor B lower the reaction rate at low substrate concentrations.
- Inhibitor B lowers the maximum reaction rate, while inhibitor A does not.
- Inhibitor A is competitive – when the concentration of substrate begins to exceed the concentration of inhibitor, the maximum rate of reaction can be achieved because the substrate has a higher chance of accessing active sites.
- Inhibitor B is non-competitive – non-competitive inhibitors bind to another site on the enzyme, and make the active site inaccessible. Increasing the substrate concentration does not decrease the inhibiting effect.
Skill: Calculating and plotting rates of reaction from raw experimental results.
A student tested the effect of hydrogen peroxide concentration on catalase activity in potato cells, using the following apparatus:
He performed five trials and averaged his results.
- Use a spreadsheet program (i.e. Excel) to plot the results for each percentage of H2O2. Download the raw data here.
- Calculate the maximum rate of reaction, and the average rate of reaction at each percentage of hydrogen peroxide, in cm3s-1.
Figure 8.2.1f – Anopheles mosquito
Malaria is transmitted by mosquito bites, and kills about one million people every year.
When you are asked to:
- explain a graph or trend, always provide a description of the trend first, then explain it using appropriate terminology.
- compare and contrast two items, always refer to both in the same sentence.
A rate of reaction should be expressed as a ratio. For example:
- volume of gas collected over time (cm3/min)
- mass of substrate lost over time (mg/hour).
Students often forget to include the time, or rate, aspect in their IAs.
Nature of Science
(image available from creative commons. Can you use it without modification?”)Chemogenomic profiling of Plasmodium falciparum as a tool to aid antimalarial drug discovery
Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4635350/