Organelles
The -elle ending on words is a diminutive meaning 'little', so organelle literally means little organ. Organelles are membrane-bound structures that have a specific function. The nucleus is an organelle whose function is to control the cell and store the hereditary molecules.
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Ribosomes
Ribosomes are the exception to the membrane-bound criterion for an organelle. They are considered organelles but are not surrounded by a membrane. Recall ribosomes are made in the nucleoli of the nucleus. They migrate into the cytoplasm after formation. They are suspended in the cytoplasm as small and large subunits. When a messenger RNA is present they join together and attach to the mRNA as a unit.They 'read' the mRNA molecule and produce proteins using the mRNA template. Some ribosomes are associated with the endoplasmic reticulum (another organelle). The area of the endoplasmic reticulum (ER) that has ribosomes attached to it is called rough endoplasmic reticulum. Ribosomes attached to the ER are shown as red dots attached to the membrane to the lower right side of the nucleus. Free ribosomes are shown in red to right above the nucleus.
