Objectives

1. Determine how a cell functions
2. Determine how a nucleus functions
3. Describe the transcription process
4. Describe the translation process and how cells produce proteins

A cell is very much like a town because, like a town, each cell has a purpose and components that are needed by other cells or communities. In a town you can find a library with copy machines and factories. Towns often contain some sort of manufacturing. In this analogy the manufacturing occurs in factories. The goods manufactured must be usable or they would not be produced. However, the goods produced are specific to each town. A cell is also like a town in the sense that it also has a library or a nucleus that contains important genetic information. Cells also contain "copy machines" to transcribe information and "factories" to produce products known as proteins (translation).

The library is analogous to the nucleus of the cell. Within the nucleus is the DNA. This is the genetic material that determines physical characteristics of the cell and ultimately the organism. DNA does not leave the nucleus. Instead, messenger RNA is used to retrieve the information from nucleus for the production of proteins outside the nucleus. The messenger RNA is a "copy" of the information contained in specific sequences of DNA. This copy (mRNA) is transported to a seperate region of the cell where proteins are made.

It is important to remember that the books cannot be removed from the library. Therefore, a copy must be made. This copy can only be used to make a certain amount of product at the factory before the copy wears out and the process must be repeated.

The copy machine is an analogy for the process of transcription. The copies are the messenger RNA (mRNA) that take the information within the nucleus and bring it to the site of translation. Translation usually occurs in the cytoplasm. Translation is the process of making the proteins in the cell. In our analogy "translation" is the process of turning the instructions into a product in the factory (see below). The mRNA has a given limited life-span and mRNA is typically broken down after a certain amount of time.

In most towns there is a factory. The production of goods is part of the economy of a town or community. It is essential for the factory of the town to be involved in production of necessary goods. As we have already learned, the information housed in the library contains blueprints or instructions on how the factory must produce the goods. The products of the cell factory are the essential building blocks for the communities. Factories in the town each produce a component of the total goods produced by the town. Each town produces its own unique set of products.

A more technical explaination of the factory of the cell would include that the factory represents the process of translation. Translation is the process of the nucleic acids being translated into the "amino acid" language.

The scheme as we have shown you is how information flows from DNA to mRNA to the protein level. This is the central concept of molecular biology. With this understanding, you will be better able to understand the concepts of genomics and biotechnology.

You should now recognize that the structure of a cell is similar analogous to a town. In addition, within each cell is the storage of information. You now realize that this information is DNA. Because DNA or books cannot be removed from the library a copy must be made. This copy is messenger RNA which is taken to the factories for the production of goods. There may be more than one factory in the town. However, each of these factories will produce a portion of the total product for the town or cell. For example, if the product for the town was a car, one factory would produce the tires while another would produce the interior. Once these products are put together, the overall outcome for the town is a car. Another set of books may be used to manufacture scissors. Similarly, cells "manufacture" many different proteins that are important for the cell, the whole organism, and how the orgamism functions in the environment.