The nucleus can be thought of as the brains of a cell. Our genetic material (DNA), in the form of chromosomes, is stored in this organelle. The nucleus (plural-nuclei) is roughly spherical and is surrounded by two membranes. As stated in the previous chapter, cellular membranes are made up of two sheets of lipids facing one another.
As shown above, the nucleus is home to chromosomes. Chromosomes are composed of long strings of DNA. As shown in the animation below, the DNA in a chromosome is highly organized and looped. The X shaped chromosome shown in the two animations on this page actually represents a chromosome that has been copied or replicated in preparation for cell division. An unreplicated chromosome consists of a single DNA molecule which can contain thousands of genes. The DNA in chromosomes acts as a kind of blueprint to guide all of the other activities in the cell.
Some key features of our genetic make-up:
- We have two sets of chromosomes; one contributed by each parent via the gamete (sperm or egg). Human cells normally contain 46 chromosomes, 23 from each parent.
- Chromosomes are made up of a complex between DNA and proteins. This complex is called chromatin.
- Genes are sections of DNA that contain the information for the production of a specific molecule such as a protein. Important in the development of cancer, small changes in the nucleotide sequence of a gene may result in the altered behavior of a cell.
Changes to the genetic material are essential for the development of cancer. We will consider how this blueprint gets read and used in the next chapter.