3. Cell Organelles

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The third chapter of our Biology e-book course for the ENEM exam will address a fundamental topic: Cell Organelles. Cell organelles are specialized structures present in the cytoplasm of eukaryotic cells. They perform several essential functions for the survival and functioning of the cell.

1. Mitochondria

Mitochondria are organelles responsible for producing energy in the cell through the process of cellular respiration. They are surrounded by two membranes: a smooth outer one and a wrinkled inner one, forming the so-called mitochondrial cristae. Inside the mitochondria, we find the mitochondrial matrix, where the chemical reactions of cellular respiration take place.

Interestingly, mitochondria have their own DNA, which suggests that these organelles may have originated from primitive bacteria that were engulfed by eukaryotic cells in a process known as endosymbiosis.

2. Endoplasmic Reticulum

The endoplasmic reticulum is a network of membranous channels that extends through the cytoplasm. It can be divided into two types: rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (REL).

The RER is so named because of the presence of ribosomes attached to its surface. It is involved in the synthesis of proteins that will be exported or incorporated into the cell membrane. The REL, which lacks ribosomes, is involved in a variety of functions, including lipid synthesis and detoxification of harmful substances.

3. Golgi Complex

The Golgi complex is an organelle made up of a series of flattened, stacked sacs called cisternae. It is involved in the modification, sorting and packaging of proteins and lipids that have been synthesized in the endoplasmic reticulum.

Proteins and lipids are transported from the endoplasmic reticulum to the Golgi complex in small vesicles. In the Golgi complex, these molecules are modified and sorted before being sent to their final destination, be it the cell membrane or the outside of the cell.

4. Lysosomes

Lysosomes are small vesicles that contain digestive enzymes. They are responsible for intracellular digestion, that is, the breakdown of complex molecules into simpler molecules that can be used by the cell.

Lysosomes also play an important role in recycling cellular components, a process known as autophagy. In addition, they can act in the body's defense, digesting bacteria and viruses that have been encompassed by the cell.

5. Peroxisomes

Peroxisomes are organelles involved in cell detoxification. They contain enzymes that neutralize toxic substances, such as hydrogen peroxide (oxygenated water), transforming them into less harmful substances.

In addition, peroxisomes are involved in the metabolization of fatty acids, an important process for obtaining energy.

Understanding the structure and function of cell organelles is fundamental to understanding the functioning of the cell as a whole. This knowledge is essential for the ENEM test, which often includes questions on this topic.

In the next chapter, we'll explore another important aspect of cell biology: the cell cycle and cell division. Stay tuned!

Next page of the Free Ebook:

44. Cell Division: Mitosis and Meiosis