Cells are the smallest anatomical unit of organisms and perform a variety of functions, encompassed in three main actions: nourishing, connecting and reproducing.
To carry out these processes, cells have organelles and other parts that allow them to relate to the environment, supplying energy to the body and creating waste during the process.
Then we will see the main parts of the cell, both plant and animal, Besides mentioning how they differ and how they perform different functions.
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 of which living things are composed. It is usually microscopic and its main areas are the nucleus, plasma membrane and cytoplasm, areas where organelles are 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 allow the cell to perform these functions and to survive and function.
The most important classification of cells is based on whether or not it has a cell nucleus.
- Prokaryotes: Unicellular organisms without a nucleus, with DNA scattered throughout 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, animal and plant, which differ in shape and organelles. Animal cells are found in animals, while plant cells, besides being found in plants, can also be found in algae.
Parts of a cell
Below, we will take a look at all the parts that make up animal and plant cells, and 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 the cell membrane or plasmalemma, it is the biological border which delimits the interior of the cell with its exterior. It covers the whole cell and its main function is to regulate the entry and exit of substances, allowing the entry of nutrients and the excretion of wastes.
It is made up of two layers in which carbohydrates, phospholipids and proteins can be found, and forms a selective permeable barrier, which means that while keeping the cell stable, giving it shape, it can change in a way. to allow entry. or release of substances.
2. Cell wall
It is a plant cell structure, such as those found in plants and fungi. It is an additional wall to the plasma membrane, which provides rigidity and strength to the cell. It is mainly composed of cellulose.
The nucleus is the structure that allows us to differentiate between eukaryotic cells, which have them, and prokaryotes, which do not. It is a structure that contains all the genetic material, its main function being to protect it.
This genetic material is organized as strands of DNA, segments are genes that code for different types of proteins. This DNA, in turn, is embedded in larger structures called chromosomes.
The other functions associated with the cell nucleus are:
- Generate messenger RNA (mRNA) and break it down into proteins.
- Generate pre-ribosomes (rRNA).
- Organize genes on chromosomes to prepare for cell division.
4. Nuclear membrane
It is a structure which, like the plasma membrane enveloping the cell, the nuclear membrane is a structure which surrounds the nucleus with a double lipid membrane, allowing communication from within itself with the cytoplasm.
It is a structure located in the nucleus. Its main function is to synthesize ribosomes, from their DNA components, in the form of ribosomal RNA (rRNA).. This is related to protein synthesis, which is why many of these nucleoli can be found in high protein synthesized cells.
Chromosomes are the structures in which genetic material is organized and are particularly visible during cell division.
It is all of the DNA, proteins, both histones and non-histones, that are found inside the cell nucleus, making up the genetic material of the cell. Its basic units of information are nucleosomes.
The cytoplasm is the internal 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 certain organelles can be found. The cytoplasm is the environment in which many important chemical processes take place throughout life.
It can be divided into two sections. One, ectoplasm, is gelatinous in consistency, while the other, endoplasm, is more fluid., Being the place where 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.
The cytoskeleton, as the name suggests, 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 made up 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 approximately 10 nanometers in size and impart tensile strength to the cell.
Microtubules are cylindrical tubes 20 to 25 nanometers in diameter, made up of units of tubulin. these microtubules they are the scaffolding that shapes the cell.
Types of organelles
As the name suggests, organelles these are small organs that are found inside the cell. Technically speaking, the plasma membrane, cell wall, cytoplasm, and nucleus are not organelles, although it is questionable whether or not the nucleus is an organelle or whether it is a structure that requires special classification. . The most important organelles of the cell, animals and plants, are:
Mitochondria are organelles found in eukaryotic cells. provide the energy necessary to carry out the activity they host. They are quite large in size compared to other organelles and their shape is globular.
These organelles break down nutrients and synthesize them into adenosine triphosphate (ATP)., Essential substance for energy. In addition, they have a reproductive capacity, as they have their own DNA, which allows more mitochondria to form depending on whether the cell needs more ATP. The higher the cell activity, the more mitochondria will be required.
The mitochondria obtain ATP as it performs cellular respiration, taking molecules from foods rich in carbohydrates which, when combined, produce this substance.
11. Golgi apparatus
The Golgi apparatus is found in all eukaryotic cells. Performs the production and transport of proteins, lipids and lysosomes inside the cell. It functions as a conditioning plant, modifying the vesicles of the endoplasmic reticulum.
It constitutes a system of endomembranes which fall back on themselves forming a kind of curved labyrinth, grouped in bags or flattened cisterns.
These are sachets that digest substances taking advantage of the nutrients they contain. They are relatively large organelles, formed by the Golgi apparatus, and they contain hydrolytic and proteolytic enzymes, Which degrade both the external and internal materials of the cell. Its shape is spherical, surrounded by a simple membrane.
Vacuoles are compartments closed by the plasma membrane that contain different fluids, water and enzymes, although they also have solid capacities such as sugars, proteins, salts and other nutrients. Most vacuoles form from membranous vesicles that come together. They are not defined and their structure varies according to the needs of the cell.
These 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 are organized which transform light energy into chemistry.
ribosomes are responsible for protein synthesis, processing what is needed for cell growth and reproduction. They are dispersed 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 the transfer or synthesis of lipids and proteins. It is distributed throughout the cytoplasm and its main function is protein synthesis. Its membranes continue into the nuclear envelope and may extend to near the plasma membrane..
There are two types: the rough endoplasmic reticulum, to which ribosomes are attached, while the other, said smooth, as the name suggests, does not.
The centriole is an organelle with a cylindrical structure, formed of microtubules. It is part of the cytoskeleton and therefore maintaining the shape of the cell, in addition to transporting organelles and particles inside the cell.
When two centrioles meet and are positioned perpendicularly, located inside the cell, it is called a diplosome. This structure is responsible for the movement of cilia and flagella of unicellular organisms.
In addition, centrioles are involved in cell division, where each centriole will be part of each of the daughter cells, serving as a mold for the formation of a new centriole in them.
plagues these are structures that not all cells have. They are characteristic of single-celled organisms or cells like sperm, and are structures that allow cell mobility.
Differences between animal and plant cells
Animal and plant cells share many similar organelles and structures, but they also exhibit certain details that distinguish them. 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.
Chloroplasts are another suitable plant structure which, as we said already, are structures where chlorophyll is found, fundamental during photosynthesis. These organelles are the ones that 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 make their own food, while those who have animals, without chloroplasts, are heterotrophs.
In animal cells, energy is only provided by mitochondria, while in plants, both mitochondria and chloroplasts are found.This allows the cell to have energy from two different organelles. This is why plant organisms can do photosynthesis and cellular respiration, while animals can only do this last biochemical process.
Another detail, perhaps not as important as being able to photosynthesize but striking, is that the vacuole in the plant cell is usually single, being centrally located, 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.
- 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: Pan-American physician. ISBN 950-06-1974-3.