A student mixes glucose, enzymes and ATP in a sealed flask, the same chemicals that a cell uses…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student mixes glucose, enzymes and ATP in a sealed flask, the same chemicals that a cell uses. At first the reactions run quickly. After an hour the amounts of every chemical stop changing. (a) What has the flask reached? (b) Is the flask alive in any sense? Explain. (c) What would have to happen to keep the reactions going? (d) Why can the flask no longer do work?
Need a reminder? The key ideaShow
Metabolism is all the chemical reactions of a living thing, in pathways of enzyme-catalysed steps. Anabolic pathways build molecules and use energy; catabolic pathways break them down and release energy, which is stored in ATP, the energy currency. Metabolic flux is the rate of flow through a pathway. A closed system reaches equilibrium: no net flow, no free energy and no work. A living cell is an open system held in a steady state far from equilibrium by a continuous flow of matter and energy.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. What the flask reached. It has reached equilibrium. The amounts have stopped changing and there is no net flow.
Step 2. Alive? No. The living state is a steady state away from equilibrium, kept up by a flow of matter and energy. The sealed flask has no such flow.
Step 3. Keeping it going. The flask would need a supply of fresh glucose and a way to remove waste. In other words, it would have to become an open system.
Step 4. Work. At equilibrium there is no net flow and no free energy is left, so nothing can drive any change.
Answer: (a) equilibrium; (b) no, it is a closed system with no flow; (c) a steady supply of glucose and a way to remove waste; (d) no free energy is left at equilibrium.
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