4d. The Ribosomes and the ER [Beyond Books

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Almost everybody has had the flu before. The flu is short for influenza virus. A virus invades a cell and forces it to use its own DNA transcripting organelles to replicate itself.

4d. The Ribosomes and the ER

The endoplasmic reticulum is like a factory conveyor belt.

The Cytoplasm: The Factory Floor

The real work of the cell occurs in the cytoplasm, the cell's "factory floor." The term "cytoplasm" refers to everything between the cell membrane and the nuclear membrane. It consists mostly of water, salts, some proteins, and many small structures called organelles (or little organs).

These structures perform several different functions for the cell which generally fall under the categories of production, maintenance, and energy transformation. This tour of the cell includes several stops on the "factory floor." Let's start with the production team.

The steps involved in building a protein.

The Endoplasmic Reticulum

In a factory, the assembly of parts takes place on the factory floor. The highly skilled craftspeople who assemble these components sit hour after hour at their stations, plugging away at their work. These workers are highly compensated because they can read plans and use that information to make different kinds of products. Each one of them has his or her own work platform, surrounded by tools. These workers do not create the product designs; rather, they read the plans sent from the executive department.

The smooth ER helps transport materials within the cell.
The cell has its own assembly line and workers. Within the cytoplasm is a series of large, flattened membranes that fold back and forth on each other and have a very large surface area. This collection of membranes is called the ENDOPLASMIC RETICULUM, or ER.

The ER stretches from the nuclear membrane to the plasma membrane. It serves as a pathway through the cytoplasm, as a support structure for the attachment of other organelles, and as a workstation for the ribosomes. The ER can be divided into two parts: the rough ER and the smooth ER.

The rough ER has ribosomes attached to it and provides a surface along which the process of protein assembly can occur. The smooth ER does not have ribosomes and is much more tubular in appearance. In some human cells, the smooth ER produces steroids; in others it regulates calcium levels. In a process that scientists still don't understand, the rough ER manufactures the membranes of the smooth ER.

Ribosomes manufacture proteins.

The Ribosomes

Ribosomes, the workers that build proteins, are manufactured by the nucleolus. They consist of two separate subunits: a large, lower subunit and a small, upper subunit. Ribosomes attach to the rough ER . Now let's take a look at how final processing occurs.

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