Cell
Each cell has a control center called a nucleus, the cell nucleus acts like the brain of the cell. The nucleus contains the information that tells the cell what to do and when to grow and divide. This information comes in the form of genes, which are contained in chromosomes. In the nucleus of most human cells (except for sperm and egg cells), there are 23 pairs of chromosomes. Although not every cell has a nucleus that is why cells are separated into to different groups eukaryotic (those with a defined nucleus) and prokaryotic (those with no defined nucleus)
Genes tell the cell what to do. Many genes tell the cell to make a certain protein that has a specific job or function in the body. Other genes help regulate how much protein another gene makes. Each human cell has about 25,000 genes.
A cell uses its genes selectively it can turn on (activate) the genes it needs at the right moment and turn off other genes that it doesn't need. Turning on some genes and turning off others is how a cell becomes specialized. That is how a cell becomes a muscle cell and not a bone cell, for example. Some genes stay active all the time to make proteins needed for basic cell functions. Others shut down when their job is finished and start again later if needed.
Genes tell the cell what to do. Many genes tell the cell to make a certain protein that has a specific job or function in the body. Other genes help regulate how much protein another gene makes. Each human cell has about 25,000 genes.
A cell uses its genes selectively it can turn on (activate) the genes it needs at the right moment and turn off other genes that it doesn't need. Turning on some genes and turning off others is how a cell becomes specialized. That is how a cell becomes a muscle cell and not a bone cell, for example. Some genes stay active all the time to make proteins needed for basic cell functions. Others shut down when their job is finished and start again later if needed.