The most important cell parts and organelles: an overview

Cells are the smallest anatomical unit of organisms, and they perform several functions, encompassed within three main actions: feeding, relating and reproducing.

To carry out these processes, cells have organelles and other parts that allow them interact with the environment, providing energy to the body and creating waste during process.

Then we will see the main parts of the cell, both plant and animal, in addition to mentioning how they differ and how they perform different functions.

• Related article: "Major cell types of the human body"

What is a cell?

Before going into more detail about what the main parts of the cell are, it is necessary to define it very briefly.

The cell is the smallest anatomical unit that living things are made up of. It is usually microscopic, and its main areas are the nucleus, the plasma membrane and the cytoplasm, areas where organelles can be found.

It is thanks to these organelles that cells can perform the three main functions for which they are considered living beings: nutrition, relationship and reproduction. It is through different biochemical processes that these organelles make the cell perform these functions and can survive and function.

Cell types

The most important classification of cells is based on function of whether or not it has a cell nucleus.

• Prokaryotes: unicellular organisms without nuclei, with DNA dispersed in the cytoplasm.
• Eukaryotes: unicellular or multicellular organisms, with a defined nucleus.

Although the differentiation between eukaryotes and prokaryotes is important, especially in the study of the evolution of species, the eukaryotic cell has been the most studied, finding two types, the animal and the vegetable, which differ in their shape and organelles. Animal cells are found in animals, while plant cells, in addition to being found in plants, can also be found in algae.

Parts of a cell

Below we will see all the parts that make up animal and plant cells, in addition to explaining what their functions are and in what type of cells they occur. In addition, we will conclude by mentioning how these two types of cells differ.

1. Plasma membrane

The plasma membrane, also called the cell membrane or plasmalemma, it is the biological border that delimits the interior of the cell with its exterior. It covers the entire cell, and its main function is to regulate the entry and exit of substances, allowing the entry of nutrients and the excretion of waste residues.

It is made up of two layers in which carbohydrates, phospholipids and proteins can be found, and constitutes a selective permeable barrier, this This means that, while keeping the cell stable, giving it shape, it can change in such a way that it allows the entry or exit substances.

2. Cellular wall

Is about a structure of the plant cell, such as those found in plants and fungi. It is an additional wall to the plasma membrane, which provides rigidity and resistance to the cell. It is made, fundamentally, of cellulose.

3. Core

The nucleus is the structure that makes it possible to differentiate between eukaryotic cells, which have it, and prokaryotes, which lack it. It is a structure that contains all the genetic material, its main function being to protect it.

This genetic material It is organized in the form of DNA chains, whose segments are genes that code for different types of proteins. This DNA, in turn, is enclosed in larger structures called chromosomes.

Other functions associated with the cell nucleus are:

• Generate messenger RNA (mRNA) and rebuild it into proteins.
• Generate pre-ribosomes (rRNA).
• Arrange genes on chromosomes to prepare for cell division.

4. Nuclear membrane

It is a structure that, like the plasma membrane surrounding the cell, the nuclear membrane is a structure that surrounds the nucleus with a double lipid membrane, allowing communication between its interior and the cytoplasm.

• You may be interested: "Nucleoplasm: what it is, parts and functions"

5. Nucleolus

It is a structure found within the nucleus. Its main function is to synthesize ribosomes, from their DNA components, to form ribosomal RNA (rRNA).. This is related to protein synthesis, for this reason, in cells with high protein synthesis many of these nucleoli can be found.

6. Chromosomes

Chromosomes are the structures in which genetic material is organized, and they are especially visible when cell division occurs.

7. Chromatin

It is the set of DNA, proteins, both histones and non-histones, found inside the cell nucleus, making up the genetic material of the cell. Its basic units of information are nucleosomes.

8. Cytoplasm

The cytoplasm is the inner environment of the cell, which could be called the body of the cell. It is a liquid environment formed mainly by water and other substances, where some organelles can be found. The cytoplasm is the environment in which many chemical processes important to life take place.

It can be divided into two sections. One, the ectoplasm, is gelatinous in consistency, while the other, the endoplasm, is more fluid, being the place where the organelles are found. This is associated with the main function of the cytoplasm, which is to facilitate the movement of cellular organelles and protect them.

9. Cytoskeleton

The cytoskeleton, as its name implies, is something like a skeleton present inside the cell, giving it unity and structure. It is made up of three types of filaments: microfilaments, intermediate filaments, and microtubules.

Microfilaments are fibers composed of very fine proteins, between 3 and 6 nanometers in diameter. The main protein that makes them up is actin, a contractile protein.

The intermediate filaments are about 10 nanometers long, and they give the cell tensile strength.

Microtubules are cylindrical tubes between 20 and 25 nanometers in diameter, made up of units of tubulin. These microtubules they are the scaffold that shapes the cell.

Types of organelles

As the name suggests, organelles are small organs found inside the cell. Technically speaking, the plasma membrane, cell wall, cytoplasm, and nucleus are not organelles, although they are. you could debate whether or not the nucleus is an organelle or if it is a structure that requires special classification. The most important organelles in the cell, both animal and plant, are the following:

10. Mitochondria

Mitochondria are organelles found in eukaryotic cells, providing the necessary energy to carry out the activity they host. They are quite larger in size compared to other organelles, and their shape is globular.

These organelles break down nutrients and synthesize it into adenosine triphosphate (ATP), a fundamental substance to obtain energy. In addition, they have reproductive capacity, since they have their own DNA, allowing the formation of more mitochondria depending on whether the cell needs more ATP. The more cellular activity, the more mitochondria will be needed.

The mitochondria obtain ATP when it performs cellular respiration, taking molecules from foods rich in carbohydrates that, when combined, produce this substance.

11. Golgi apparatus

The Golgi apparatus is found in all eukaryotic cells. Executes the production and transport of proteins, lipids and lysosomes within the cell. It works as a packing plant, modifying vesicles from the endoplasmic reticulum.

It constitutes a system of endomembranes that fold back on themselves forming a kind of curved labyrinth, grouped in flattened saccules or cisterns.

12. Lysosomes

They are sachets that digest substances, taking advantage of the nutrients found in them. They are relatively large organelles, formed by the Golgi apparatus, and contain hydrolytic and proteolytic enzymes inside, which degrade both external and internal material of the cell. Its shape is spherical, surrounded by a simple membrane.

13. Vacuole

Vacuoles are compartments closed by the plasma membrane that contain different fluids, water and enzymes, although they can also harbor solids such as sugars, proteins, salts and others nutrients. Most vacuoles are formed from membranous vesicles that stick together. They are not of definite shape, and their structure varies depending on the needs of the cell.

14. Chloroplasts

They are organelles typical of the plant cell, in which chlorophyll is found, an essential substance for photosynthesis. They are surrounded by two concentric membranes, which contain vesicles, the thylakoids, in where pigments and other molecules are organized that convert light energy into chemistry.

15. Ribosomes

Ribosomes are responsible for the synthesis of proteins, processing what is necessary for cell growth and reproduction. They are scattered throughout the cytoplasm, and are responsible for translating the genetic information obtained from DNA into RNA.

16. Endoplasmic reticulum

It is a channel system responsible for transferring or synthesizing lipids and proteins. It is distributed throughout the cytoplasm, and its primary function is protein synthesis. Their membranes continue with the nuclear envelope and can extend close to the plasma membrane..

There are two types: the rough endoplasmic reticulum has ribosomes attached to it, while the other, called smooth, as its name suggests, does not.

17. Centriole

The centriole is an organelle with a cylindrical structure, which is made up of microtubules. It is part of the cytoskeleton and therefore maintain the shape of the cell, in addition to transporting organelles and particles inside the cell.

When two centrioles meet together and are positioned perpendicularly, located inside the cell, it is called a diplosome. This structure is responsible for the movement of the cilia and flagella of single-celled organisms.

In addition, the centrioles are involved in cell division, where each centriole will be part of each one of the daughter cells, serving as a template for the formation of a new centriole in them.

18. Flagella

Flagella are structures that not all cells have. They are characteristic of unicellular organisms or of cells such as sperm, and are structures that allow the mobility of the cell.

Differences between animal and plant cells

Both the animal and plant cells share many similar organelles and structures, but they also have certain details that allow them to be distinguished. The most notable is the presence of the plant wall in the plant cell, which covers the plasma membrane, giving the cell a hexagonal and rigid shape.

Another properly vegetal structure is the chloroplasts which, as we were already saying, are structures where chlorophyll is found, which is essential during photosynthesis. These organelles are what allow the plant cell to synthesize sugars from carbon dioxide, water and sunlight. Thanks to this, we say that organisms with this type of cells are autotrophs, that is, they manufacture their own food, while those that have it animal, lacking chloroplasts, are heterotrophs.

In animal cells, energy is provided only by mitochondria, while in plant cells both mitochondria and chloroplasts are found, which allows the cell to draw energy from two different organelles. This is the reason why plant organisms can do photosynthesis and cellular respiration, while animals can only do the latter biochemical process.

Another detail, perhaps not as important as the fact of being able to carry out photosynthesis but yes striking, is that the vacuole in the plant cell is usually unique, being located in the center and being very big. On the other hand, in the animal cell, there are several vacuoles and these are usually much smaller. In addition, in the animal cell there are centrioles, a structure that is not found in the plant.

Bibliographic references:

• Alberts et al (2004). Molecular biology of the cell. Barcelona: Omega. ISBN 54-282-1351-8.
• Lodish et al. (2005). Cellular and molecular biology. Buenos Aires: Panamerican Medical. ISBN 950-06-1974-3.