Parts of a Human Cell

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The cell is the main building unit for all living organisms, from bacteria to humans. All complex organs and systems are made up from billions of individual cells working together, but also individually. In the human body, cells come in different shapes depending on the tissue they belong to. However, all cells have four parts in common: the plasma membrane, cytoplasm, ribosomes, and DNA.

The plasma membrane (also called the cell membrane) is a thin coat of lipids that surrounds the cell. It forms the physical boundary between the cell and its environment and therefore is very important for all interactions between the cell and the outside. Many proteins assist with these interactions by docking on the plasma membrane and binding to outside molecules. Furthermore, cells can send signaling molecules through their plasma membrane to communicate messages to other parts of the tissue or body.

Next, the cytoplasm refers to all of the cellular material inside the plasma membrane, other than the nucleus. Cytoplasm is gel-like in its texture and contains mostly water, salt and other molecules, as well as all organelles that assist with cellular function, such as ribosomes.

Ribosomes are structures in the cytoplasm where proteins are made. They consist of RNA molecules and proteins, and their main role is to translate genetic sequences to proteins. Each cell may have a large number of ribosomes which either exist as free particles in the cytoplasm, or are organized in larger structures.

Finally, the DNA is a nucleic acid that contains all the necessary genetic information for the cell to function. The DNA is usually tightly packed in the nucleus of the cell, where it is protected from the outside environment. If we were to measure the length of a DNA molecule, each cell alone contains about 6 feet of DNA. The human DNA contains about 25,000 gene sequences, as well as many sequences that do not encode proteins and are either evolutionary remnants or regulatory components.