The nucleus is an organelle within a cell that processes information. It is also the administrative center. The nucleus stores the cell's genetic material and coordinates various cellular activities such as growth and reproduction.
The nucleus is found in eukaryotes, which is a group that includes plants and animals. Most cells only have one nucleus, with the exception of some types of algae. Prokaryotes, which are simpler organisms like bacteria, do not have a nucleus. In prokaryotic cells, the cytoplasm acts as the cell's administrative center. The cytoplasm also contains the cell's information. Each nucleus takes up approximately 10 percent of space in the surrounding cell. The nucleus is separated by a thick double membrane, called the nuclear envelope, from the cytoplasm, which contains a liquid substance and houses other cell components. The nuclear envelope plays an important role in the transport of materials; its small holes, called nuclear pores, allow molecules to pass back and forth between the cytoplasm and the nucleus. The endoplasmic reticulum, which is a network of sacs and tubules, connects the nuclear ribosome with other cell structures called ribosomes.
Components of the Nucleus
The inner part of the nucleus contains the nucleoplasm. Inside this semifluid structure is chromatin, which is a form of deoxyribonucleic acid (DNA) that forms chromosomes during the processes of mitosis and cell division. The nucleus also contains nucleoli, which help to synthesize ribosome and other components such as Gemini of coiled bodies, also called GEMS, and Cajal bodies. Chromatin and chromosomes, which are located in the nucleus, contain the cell's DNA. In humans, these structures contain approximately 6 feet of DNA. The DNA is structured into chromatin, which are string-like fibers. Chromatin also contain proteins. The nucleolus is another part of the nucleus. This part of the nucleus produces ribosomes, which have the essential task of protein production. Each cell can contain up to four nucleoli. During cell division, the nucleoli disappear. The nuclear envelope surrounds the nucleus, giving it protection through a double-walled membrane. The area between the two membranes of the nuclear envelope is called perinuclear space, and it connects the nuclear envelope to the endoplasmic reticulum. The inner layer of the nuclear envelope contains nuclear lamina, which shares a bond with chromatin and other components. The nuclear envelope unravels during cell division or mitosis, but it reforms once those processes are complete.
Other Cell Features
Although not all cells contain a nucleus, they have four parts in common. All cells have a cytoplasm, a plasma membrane, DNA and ribosomes. The plasma membrane, also called the cell membrane, surrounds cells to form a buffer between them and their environments. The cytoplasm refers to all materials within the membrane except for the nucleus. It is comprised of cytosol, which is a watery substance, and several other cell structures, including ribosomes. The DNA contains each cell's unique genetic information. Although cells share some common components, they vary widely in size, shape and function. They exist in all parts of the body, including skin, muscles and organs. Some cells have special adaptations to their environments. Algae cells, for instance, have tail-like structures called flagella that help them swim. The spikes on pollen grains help them stick to insects.