The rough endoplasmic reticulum is given its name due to the ribosomes present within its membrane. These ribosomes are able to translate proteins, which are then modified within the endoplasmic reticulum and sent to the Golgi apparatus.

Ribosomes are the only cellular machinery capable of translating RNA into proteins.

The endoplasmic reticulum is an organelle that manufactures proteins, steroid molecules, cholesterol, and other lipids. The rough endoplasmic reticulum is embedded with ribosomes to allow polypeptides to be translated into the interior of the organelle. The smooth endoplasmic reticulum is responsible for lipid synthesis and degradation of toxins.

The mitochondria are the powerhouses of the cell. They extract energy by breaking down nutrients and converting carbohydrates to ATP. The citric acid cycle and electron transport chain take place within the mitochondria.

Some of the main differences between plant and animal cells are the presence of a cell wall in plant cells, which maintains a regular and rigid cell shape, and chloroplasts, which are the sites of photosynthesis in plant cells. By contrast, animal cells do not have a cell wall, allowing their cell shape to be more irregular and more dependent on cytoskeletal filaments. Animal cells do not perform photosynthesis and therefore do not have chloroplasts. Some, not all, animal cells contain many small vacuoles. 

A centriole is a cylindrical structure present in pairs in most eukaryotic cells. They are composed of microtubules arranged in nine triplets and play a role in mitosis and meiosis. During these processes, the centrioles are replicated and each pair migrates to a cell pole. From the centrioles, mitotic spindles emanate to attach to the centromeres of sister chromatids located at the metaphase plate. 

The Golgi apparatus is composed of compartments that are organized into a cis and a trans face. The cis face receives proteins from vesicles originating from the endoplasmic reticulum. After fusing with the Golgi apparatus, the proteins are modified and move through the folds, or cisternae, of the Golgi to the trans face. At the trans face, the modified proteins are organized and transported by vesicles from the Golgi apparatus to their final destinations.

Ribosomes, the sites of protein synthesis, are found through the cytoplasm, and in eukaryotes, on the endoplasmic reticulum. Ribosomes are assembled in the nucleolus, where rRNA (ribosomal RNA) is transcribed. Ribosomes are made of rRNA and protein, so the ribosomal proteins are synthesized on the rough endoplasmic reticulum, and are transported into the nucleolus to be assembled into ribosomes.

Smooth ER lacks ribosomes and functions in diverse metabolic process such as synthesis of lipids, metabolism of carbohydrates, and detoxification of drugs and poisons. Rough ER contains ribosomes on its surface and functions in protein synthesis. Bacteria lack endoplasmic reticulum since it is membrane-bound.

While most of a cell's DNA is located in the nucleus, some DNA is found in the mitochondria and chloroplasts. The DNA found in plasmids supports the endosymbiotic theory. The cytoplasm of eukaryotes does not contain free floating DNA like in prokaryotes.

Extranuclear genes, also known as cytoplasmic genes, are genes located outside the nucleus. They can be found in other parts of the cell, such as the mitochondrion, chloroplasts, and other plastids. Each of these organelles is thought to have originally been an independent prokaryotic cell, ingested by another cell, known as the endosymbiotic theory. Each of these organelles has its own DNA and works in cooperation within the nuclear DNA.