Structure of Cell Organelles

Cells, the smallest systems able to retain existing and reproducing capabilities, provide life to all organisms – from single-celled plant life to multibillion-celled animals. How we think about cell structure has changed significantly in the last few years. Early biologists regarded cells as simple membrane sacs containing a liquid and some suspended particles. Biologists today know that cells are infinitely complex. 

Cells come in various types, shapes and sizes. For illustration purposes, let us discuss a  generalised version of a cell that includes features for all cell types. 

A cell comprises three parts: the cell membrane, the nucleus, and the cytoplasm. There are complex arrangements of fine fibres and hundreds or thousands of small but distinct structures called organelles within the cytoplasm.

What are cell organelles?

Cell organelles form the basic structure of cells, the unit of life. The cell organelles are intracellular compartments that perform various functions of a cell. 

What do these cell organelles do? Organelles do a lot of work – from regulating transcription to storing water and producing energy. Cells work together to form the tissues that form organs that come together to make organ systems and ultimately multicellular organisms. 

If a cell can be considered a factory, then the various departments and workers within the factory are the cell organelles. Everyone has a specific task, but everyone works together to complete the task. 

Classification based on the structure of cell organelles

The structure of cell organelles plays an essential role in their functions. 

According to the presence or absence of membrane, various cell organelles are classified into three categories.

• Double membrane-bound organelles: The mitochondria, nucleus and chloroplasts are bilayer-bound organelles that exist only in eukaryotic cells.
• Single membrane-bound organelles: Vacuoles, lysosomes, Golgi apparatus, and endoplasmic reticulum are individual membrane-bound organelles found only in eukaryotic cells.
• Organelles without membrane: Ribosomes,  cytoskeletons are organelles that are not attached to the membrane. They are present in both prokaryotic and eukaryotic cells.

Structure and function of cell organelles

What are the eight cell organelles necessary for the survival of the cell? 

Here, we discuss the structure of cell organelles and the functions of the eight important organelles.

1. Nucleus: The nucleus is a bilayered- membrane organelle found in all eukaryotic cells. It acts as a control centre for cell activity and is the largest organelle. It is a repository of cellular DNA. Due to its structure, the nucleus is dark, round and surrounded by a nuclear envelope. A porous membrane (like a cell membrane) forms a wall between the cytoplasm and the nucleus. Inside the nucleus are small spheres called nucleoli. It also carries essential structures called chromosomes.

1. Mitochondria: They are also known as the powerhouse of the cell because they produce high-energy molecules. Some organisms maternally inherit the mitochondrial genome. It is a double membrane-bound organelle found in almost all eukaryotic cells. The membrane divides its lumen into two different aqueous chambers. The inner compartment, called the matrix, folds into cristae, and the outer membrane is continuous and forms a boundary. They usually vary in size and are either circular or oval. Mitochondria are the sites of aerobic respiration in cells that generate energy in the form of ATP and aid in converting molecules.

1. Endoplasmic Reticulum: The endoplasmic reticulum is a network of membranous channels filled with fluid. They are the cell’s transport system and move substances around the cell. They are of two types: rough endoplasmic reticulum and smooth endoplasmic reticulum. The rough ER is found throughout the cell and are composed of tubules, cisterna and vesicles involved in protein production. The smooth ER is a storage organelle associated with the production of lipids and steroids, and it also performs cell detoxification.

1. Golgi Apparatus: The Golgi apparatus, also known as the Golgi complex, is a membrane-bound organelle composed primarily of flat, stacked sacs called cisternae. This organelle is mainly responsible for modifying, transporting and packaging proteins and lipids to specific target sites. The Golgi apparatus is located in the cytoplasm of cells and is present in both plant and animal cells. 

1. Ribosomes: Ribosomes are important non-membrane bound cytoplasmic organelles associated with the endoplasmic reticulum. Ribosomes are found in many cells in small particles and are composed primarily of two-thirds RNA and one-third protein.

1. Vacuole: Vacuoles are commonly defined as irregularly shaped storage sacs inside cells. They are organelles that are filled with fluid and surrounded by a membrane. Vacuoles store food or nutrients that cells may need to survive.

1. Lysosomes: Lysosomes are membrane-bound organelles that contain digestive enzymes. Lysosomes are involved in a variety of cellular processes. They mainly break down excess or worn cell parts.

1. Cytoskeletons: Cytoskeletons are a network of filamentous proteinaceous structures that pass through the cytoplasm from the nucleus to the plasma membrane. They are found in all living cells, especially eukaryotes. The cytoskeleton matrix is ​​composed of types of proteins that can rapidly divide or degrade according to the needs of the cell.

Conclusion

A cell is a complex unit of life comprising organelles performing various functions. The structure of cell organelles helps us understand each organelle’s utility and function. The cell organelles are both membrane-bound and non-membrane bound living units that reside within the cell and differ in structure and function. They are necessary for the normal functioning of the cells. Some organelles work on giving shape and support, while others are involved in cell movement and regeneration. Studying the structure of cell organelles is vital for understanding each organelle’s function and how they contribute to the survival of the cell.