Metabolic Pathways and Enzyme Power
Every living cell performs thousands of chemical conversions each second, yet most of these reactions would be far too slow on their own. Enzymes solve this problem by lowering the energy barrier between substrate and product.
This quiz tests two connected ideas:
- How individual enzyme-catalysed steps are linked into metabolic pathways, using the glucose-to-pyruvic-acid sequence as the central example.
- How enzymes form a transient enzyme-substrate complex, pass through a transition state, and reduce activation energy without changing the overall energy difference between substrate and product.
You will also meet the dramatic scale of enzyme catalysis, the branching of one pathway into lactic acid, pyruvic acid or ethanol, and the reading of the energy diagram. Work carefully through each question and read every explanation.
Q1. A multistep chemical reaction in which each step is catalysed by the same enzyme complex or by different enzymes is called:
The lesson defines a metabolic pathway as a multistep chemical reaction where each step is catalysed by the same enzyme complex or by different enzymes.
Q2. In the absence of any enzyme, approximately how many molecules of ##\ce{H2CO3}## are formed per hour during the hydration of carbon dioxide?
Without an enzyme the reaction is very slow, forming about 200 molecules of ##\ce{H2CO3}## per hour.
Q3. With carbonic anhydrase present in the cytoplasm, about how many molecules are formed every second?
Carbonic anhydrase speeds the reaction dramatically, with about 600,000 molecules formed every second.
Q4. By approximately what factor does carbonic anhydrase accelerate the hydration of carbon dioxide?
The lesson states that the enzyme accelerates the reaction rate by about 10 million times.
Q5. Glucose becomes pyruvic acid through how many different enzyme-catalysed metabolic reactions?
The lesson states that glucose becomes pyruvic acid through ten different enzyme-catalysed metabolic reactions.
Q6. In skeletal muscle under anaerobic conditions, the glucose-to-pyruvic-acid pathway leads to the formation of:
In skeletal muscle under anaerobic conditions, lactic acid is formed.
Q7. In yeast during fermentation, the same pathway leads to the production of:
In yeast during fermentation, the same pathway leads to the production of ethanol, that is, alcohol.
Q8. Under normal aerobic conditions, the product formed from the glucose pathway is:
Under normal aerobic conditions, pyruvic acid is formed.
Q9. The chemical which is converted into a product during an enzyme-catalysed reaction is called the:
The chemical which is converted into a product is called a substrate.
Q10. The substrate must bind the enzyme at its active site, forming an obligatory complex abbreviated as:
There is an obligatory formation of the enzyme-substrate complex, written as ##\ce{ES}##, where E stands for enzyme.
Q11. Which statement best describes the enzyme-substrate complex?
The lesson states that the formation of the ES complex is a transient phenomenon.
Q12. While the substrate is bound to the enzyme active site, a new structure of the substrate called the:
During the state where substrate is bound to the active site, a new structure of the substrate called the transition state structure is formed.
Q13. On the energy diagram of a reaction, the y-axis represents:
The y-axis represents the potential energy content, while the x-axis represents the progression of the structural transformation.
Q14. Activation energy is defined as the difference in average energy content of the substrate from that of:
The difference in average energy content of S from that of the transition state is called activation energy.
Q15. What do enzymes do to the energy barrier of a reaction?
Enzymes bring down the energy barrier, making the transition of substrate to product easier, without altering the overall energy difference between S and P.