The most important parts of the cell and organelles: a summary

A review of the different parts of the animal cell and the plant cell, including organelles.

Cells are the smallest anatomical unit of organisms, and perform various functions, encompassed within three main actions: nourishment, relationships and reproduction.

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

We will now take a look at the main parts of the cell. we will see the main parts of the cell, both plant and animal, as well as how they differ from each other.We will also mention how they differ and how they perform different functions.

What is a cell?

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

The cell is the smallest anatomical unit of which all living things are composed.. It is usually microscopic, and its main areas are the nucleus, the plasma membrane and the cytoplasm, areas in which 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 by means of different biochemical processes that these organelles enable the cell to perform these functions and to survive and function.

Cell types

The most important classification of cells is based on whether or not they have whether or not they have a cell nucleus.

• Prokaryotes: unicellular organisms without a nucleus, 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, with two types, animal and plant, which differ in their shape and organelles. two types, animal and plant, 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

In the following we will see all the parts that make up animal and plant cells, as well as explain 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 cell membrane or plasmalemma, is the Biological boundary that delimits the cell's interior from 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 formed by two layers in which glucids, phospholipids and proteins can be found, and constitutes a selective permeable barrier, which means that, while it keeps the cell stable, giving it shape, it can change in such a way as to allow the entry or exit of substances.

2. Cell wall

This is a structure specific to the plant cell, like those found in plants and fungi.. It is an additional wall to the plasma membrane, which gives rigidity and resistance to the cell. It is formed, fundamentally, of cellulose.

3. Nucleus

The nucleus is the structure that differentiates between eukaryotic cells, which have it, and prokaryotic cells, which lack it. It is a structure that contains all the genetic material, and its main function is to protect it.

This genetic material is organized in the form of DNA chains, the segments of which 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 reassemble it into proteins.
• Generate pre-ribosomes (rRNA).
• Organize genes into chromosomes in preparation for cell division.

4. Nuclear membrane

It is a structure that, like the plasma membrane enveloping the cell, the nuclear membrane is a structure that envelops the nucleus with a double lipid membrane, allowing communication between the interior of the nucleus and the cytoplasm.

5. Nucleolus

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

6. Chromosomes

Chromosomes are the structures in which the genetic material is organized, and 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, 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 consisting mainly of water and other substances, in which some organelles can be found. The cytoplasm is the medium in which many chemical processes important for life take place.

It can be divided into two sections. One, the ectoplasm, has a gel-like consistency, while the other, the endoplasm, is more fluid.The endoplasm, 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 cell organelles and to protect them.

9. Cytoskeleton

The cytoskeleton, as its name suggests, is something like a skeleton present inside the cell, giving it unity and structure. It is composed 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 composes them is actin, a contractile protein.

The intermediate filaments are about 10 nanometers long, and provide tensile strength to the cell.

Microtubules are cylindrical tubes between 20 and 25 nanometers in diameter, composed of tubulin units. These microtubules are the scaffold that gives shape to the cell..

Types of organelles

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

10. Mitochondria

Mitochondria are organelles that are found in eukaryotic cells, They provide the energy necessary to carry out the activity that they contain.. They have a much larger size compared to other organelles, and their shape is globular.

These organelles break down nutrients and synthesize them into adenosine triphosphate (ATP), an essential substance for energy.which is the fundamental substance for obtaining energy. In addition, they have reproductive capacity, since they have their own DNA, allowing more mitochondria to form depending on whether the cell needs more ATP. The more cellular activity, the more mitochondria are needed.

The mitochondrion obtains ATP when it carries out cellular respiration, taking molecules from carbohydrate-rich foods which, when combined, produce this substance.

11. Golgi apparatus

The Golgi apparatus is found in all eukaryotic cells. It executes the production and transport of proteins, lipids and lysosomes within the cell.. It functions as a packaging 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 cisternae.

12. Lysosomes

These are small sacs that digest substances, taking advantage of the nutrients found in them. They are relatively large organelles, formed by the Golgi apparatus, and contain hydrolytic enzymes. contain in their interior hydrolytic and proteolytic enzymes.which degrade both external and internal material of the cell. They are spherical in shape, 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 other nutrients. Most vacuoles are formed from membranous vesicles that are joined together. They are not of defined shape, and their structure varies according to the needs of the cell.

14. Chloroplasts

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

15. Ribosomes

The ribosomes are responsible for protein synthesis, processing what is necessary for cell growth and reproduction.. They are scattered throughout the cytoplasm, and are responsible for translating genetic information obtained from DNA into RNA form.

16. Endoplasmic reticulum

It is a system of channels responsible for transferring or synthesizing lipids and proteins. It is distributed throughout the cytoplasm, and its primary function is protein synthesis. Its membranes continue with the nuclear envelope and can extend to near 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 of cylindrical structure, which is formed on the basis of microtubules. It is part of the cytoskeleton and, therefore, maintain the shape of the cell, as well as transport 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 unicellular organisms.

In addition, the centrioles are involved in cell division, where each centriole will form part of each of the daughter cells, serving as a mold for the formation of a new centriole in those cells.

18. Flagella

Flagella are structures that not all cells possess.. They are characteristic of unicellular organisms or of cells such as spermatozoa, and are structures that allow the cell to move.

Differences between animal and plant cells

Both the animal and plant cell share many similar organelles and structures, but they also present 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 rigid hexagonal shape.

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

In animal cells, energy is provided only by the mitochondria, whereas in plant cells, both mitochondria and chloroplasts are present, allowing the cell to have energy available from two different organelles.This allows the cell to draw energy from two different organelles. This is the reason why plant organisms can carry out photosynthesis and cellular respiration, while animals can only carry out the latter biochemical process.

Another detail, perhaps not as important as the fact of being able to perform photosynthesis but striking, is that the vacuole in the plant cell is usually unique, being located in the center and very large. In contrast, 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 cell.

Bibliographical 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: Médica Panamericana. ISBN 950-06-1974-3.