Inside the membrane, a cell is divided into small structures called organelles, each with its own job. Together they let the cell make energy, build proteins and clear waste.
Nucleus
The nucleus holds the DNA and controls the cell by deciding which genes are used. Mature red blood cells have no nucleus, which leaves more room for hemoglobin.
Mitochondria
Mitochondria use oxygen to turn glucose and fat into ATP, the cell's energy currency. Without enough oxygen the cell switches to a far less efficient process that produces lactate.
Ribosomes and endoplasmic reticulum
Ribosomes build proteins, many of them on the rough endoplasmic reticulum. The smooth endoplasmic reticulum makes lipids and, in liver cells, helps break down drugs and toxins.
Golgi, lysosomes and cytoskeleton
The Golgi apparatus packages proteins for export. Lysosomes digest worn-out parts and bacteria, and the cytoskeleton gives the cell its shape and helps it move.
| Organelle | Main job | Clinical link |
|---|---|---|
| Nucleus | Stores DNA | Target of many cancer drugs |
| Mitochondria | Make ATP with oxygen | Lactate rises when oxygen is short |
| Smooth ER | Makes lipids, breaks down drugs | Liver processing of medicines |
| Lysosomes | Digest waste and bacteria | Lysosomal storage diseases |
At the bedside
A high lactate level in a sick patient often means cells are not getting enough oxygen, as in shock or sepsis. It is a signal to support the circulation quickly.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).