Essential Organelles: Structures & Functions of Eukaryotic Cells
Key Organelles and Structures of Eukaryotic Cells
The Nucleolus
The nucleolus is a region within the nucleus, considered an organelle. Its primary function is the production and assembly of ribosomal components.
The Cell Nucleus
The cell nucleus is a membranous organelle found in eukaryotic cells. It contains most of the cell’s genetic material, organized into multiple long, linear DNA molecules complexed with various proteins like histones to form chromosomes. The collection of genes on these chromosomes constitutes the nuclear genome. The nucleus’s core function is to maintain the integrity of these genes, control cellular activities, and regulate gene expression. Thus, the nucleus is considered the control center of the cell’s supramolecular complexes.
Ribosomes
The ribosomes are responsible for synthesizing proteins from the genetic information of DNA, which reaches them in the form of transcribed messenger RNA (mRNA).
Vesicles
Vesicles in cell biology are small, enclosed compartments separated from the cytoplasm by a lipid bilayer. They act as cellular membranes that store, transport, or digest waste products and cellular materials.
Rough Endoplasmic Reticulum (RER)
The rough endoplasmic reticulum (RER), also called granular endoplasmic reticulum or ergastoplasm, is an organelle responsible for the synthesis and transport of proteins.
Golgi Apparatus
The Golgi apparatus is an organelle found in all eukaryotic cells, except red blood cells and epidermal cells. It belongs to the cell’s endomembrane system within the cytoplasm. It comprises approximately 4-8 dictyosomes, which are membrane-enclosed, flattened sacs stacked one above the other, whose role is to complete the manufacture of certain proteins.
The Cytoskeleton
The cytoskeleton is a three-dimensional protein network that provides internal support for cells, anchors their internal structures, and is involved in cell movement and division. In eukaryotic cells, it consists of microfilaments, intermediate filaments, and microtubules, whereas in prokaryotes, it is mainly composed of structural proteins FtsZ and MreB.
Smooth Endoplasmic Reticulum (SER)
The smooth endoplasmic reticulum (SER) is a network of tubules and membranes involved in cellular transport and the synthesis of triglycerides, phospholipids, and steroids. It also contains detoxifying enzymes that metabolize alcohol and other chemical substances.
Mitochondria
The mitochondria are membranous organelles found in most eukaryotic cells. Their size ranges from 0.5-10 micrometers (µm) in diameter. Mitochondria are sometimes described as the “power generators” of cells because they produce most of the adenosine triphosphate (ATP) supply, used as a source of chemical energy. In addition to providing energy to the cell, mitochondria are involved in other processes such as cell signaling, cell differentiation, programmed cell death, cell cycle control, and cellular growth.
Peroxisomes
Peroxisomes are common cytoplasmic organelles in the form of vesicles containing oxidases and catalases. These enzymes act in cellular detoxification. Like all organelles, peroxisomes are found only in eukaryotic cells. Their function includes an essential role in lipid metabolism, especially in the oxidation of short-chain and very long-chain fatty acids for complete oxidation in mitochondria, and in the side-chain oxidation of cholesterol, needed for the synthesis of bile acids.
The Cytoplasm
The cytoplasm is the part of the protoplasm in a eukaryotic cell, located between the nucleus and the plasma membrane. It consists of a colloidal emulsion with a very fine granular appearance, known as cytosol or hyaloplasm, and a variety of cellular organelles that perform different functions. Its primary function is to host cell organelles and contribute to their movement.
Lysosomes
The lysosomes are relatively large organelles formed by the rough endoplasmic reticulum (RER) and then packaged by the Golgi complex. They contain hydrolytic and proteolytic enzymes used to digest material of external origin (heterophagy) or internal origin (autophagy) that reaches them. In other words, they handle cellular digestion.
Centrioles
The centrioles are a pair of hollow, cylindrical structures that are part of the cytoskeleton. They are organelles involved in cell replication, with a diplosome (a pair of centrioles) typically present only in animal cells. Centrioles are two cylindrical structures surrounded by a dense protein material called pericentriolar material. Together, they constitute the centrosome or MTOC (Microtubule Organizing Center), which allows microtubule polymerization from tubulin dimers that make up the cytoskeleton. The centrioles are positioned perpendicular to each other.