cell
Meaning of cell: Everything a body does happens inside one of these compartments, which is why disease is ultimately described at this scale.
Definition of cell
A cell is the smallest unit of life that can sustain itself, and the basic building block of every tissue in the body. A membrane keeps its contents separate from the outside, and inside sit specialized structures that make energy, build proteins and, in most human cells, store DNA in a nucleus. Different tissues use differently specialized cells.
What is inside a cell?
| Structure | What it does |
|---|---|
| Cell membrane | Encloses the cell and controls what enters and leaves |
| Nucleus | Holds the chromosomes and controls which genes are read |
| Mitochondria | Release energy from nutrients and store it in a usable form |
| Ribosomes | Assemble proteins from the instructions carried out of the nucleus |
| Endoplasmic reticulum and Golgi | Fold, modify and package proteins for export |
| Lysosomes | Break down worn-out parts and material taken in from outside |
| Cytoskeleton | Gives shape, moves contents and drives division |
The membrane is not a simple bag: it is studded with pumps, channels and receptors, and most drugs act on proteins sitting in it.
How different can cells be from each other?
They vary enormously in size, shape and lifespan while sharing the same basic parts. A nerve cell can stretch from the spinal cord to the foot; a red blood cell is a small flexible disc with no nucleus at all; a sperm cell is mostly tail; a fat cell is mostly stored oil. Lifespans differ just as much, from a few days for the cells lining the gut to a lifetime for most neurons. Human cells are eukaryotic, meaning their DNA is enclosed in a nucleus, which distinguishes them from bacteria, whose DNA lies loose in the cell. Viruses are not cells at all and cannot reproduce without borrowing the machinery of one.
Why is disease described at cell level?
Because that is where most of it starts. Cancer is a failure of the controls on cell division and cell death. Inherited disease usually traces to one altered instruction that changes one protein inside cells. Infection turns on whether an organism can enter, survive in or destroy cells. A heart attack is the death of muscle cells starved of oxygen, and an autoimmune disease is immune cells attacking the body's own. Treatment follows the same logic, aiming at a receptor, an enzyme or a pathway inside a particular kind of cell, which is why a pathologist looking at cells under a microscope still decides so much.
Used in a sentence
The biopsy sample was examined under a microscope to assess the appearance of the individual cells.
Good to know
A cell's behavior, including how it divides and whether it responds to normal growth signals, is central to distinguishing normal tissue from abnormal or cancerous tissue under microscopic examination.
Word origin
Where “cell” comes from
From Latin cella, meaning small room or chamber, applied to biological cells because of their resemblance to the small compartments seen under early microscopes.