cellular metabolism
Meaning of cellular metabolism: Two opposite streams of chemistry running at once inside every cell, one tearing molecules down and one building them up.
Definition of cellular metabolism
Cellular metabolism is the full set of chemical reactions taking place inside a cell. Some reactions break molecules apart to release energy, while others spend that energy building the proteins, fats and genetic material the cell needs. The two streams run together, controlled step by step by enzymes, so that supply matches demand from moment to moment.
What are the two halves?
| Catabolism | Anabolism | |
|---|---|---|
| Direction | Breaks large molecules into small ones | Assembles small molecules into large ones |
| Energy | Releases it | Consumes it |
| Examples | Breaking down glucose, burning fat | Building protein, storing glycogen, copying DNA |
| Dominant during | Fasting, illness, hard exercise | Feeding, growth, healing |
The balance between the two decides whether tissue is gained or lost, which is why a long illness wastes muscle even when a person is being fed.
How does a cell get energy from food?
Glucose is first split in the fluid of the cell into two smaller molecules, a step yielding a little energy and needing no oxygen. When oxygen is available, those pieces enter the mitochondria, where a cycle of reactions strips electrons from them. The electrons pass down a chain of proteins, and the energy released pumps protons across a membrane. Protons flowing back through a turbine like enzyme drive the manufacture of ATP. This is what aerobic metabolism means, and it extracts many times more energy than the oxygen free route.
What happens without oxygen?
A cell short of oxygen falls back on the first step alone and converts the product to lactate so the process can keep turning over. It is fast but wasteful, and acid accumulates. Muscle does this during a sprint. Tissue cut off from its blood supply does it during a heart attack, and the acid is part of the injury. Many tumor cells favor this route even when oxygen is plentiful, a peculiarity that has been studied intensively.
How is it controlled?
Every step is run by an enzyme, and enzymes are switched up or down by hormones, by the products of the reactions themselves, and by how much raw material is available. Insulin pushes cells toward storage and building, while glucagon and adrenaline push them toward breakdown. Whole body metabolism is the sum of this activity across every cell, which is why thyroid disease, by shifting the rate everywhere at once, changes weight, temperature and heart rate together.
Used in a sentence
The study measured how cellular metabolism shifted when the oxygen supply to the tissue was reduced.
Good to know
The balance between breakdown and building shifts toward breakdown during serious illness, which is why muscle is lost over a long hospital stay even when nutrition is being provided.
Word origin
Where “cellular metabolism” comes from
Metabolism comes from the Greek metabole, meaning change, and cellular from the Latin cellula, meaning small room.