In nature there are two Cell types: prokaryotic cells and eukaryotic cells. Animals, fungi and plants are made up of eukaryotic cells, while bacteria and archaea are made up of prokaryotic cells.
Without exception, all living things on the planet, no matter what size or shape they are, are made up of cells. For this reason, scientists say that cells are the basic units of living organisms..
Most cells are very small in size, practically invisible to the naked eye, so special optical instruments are needed to observe them. These instruments are known as microscopes and his invention was the key to the discovery of these little "bricks".
In addition to animals and plants, there are countless microscopic beings in the world that are unicellular organisms, that is, they are made up of a single cell. Inside these, exactly the same processes occur as in larger organisms, which are made up of billions of cells..
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Whether they belong to a multicellular organism (with many cells) or a unicellular microbe, all cells share certain attributes that allow us to identify them as cells, among which we can mention 3 that are very important:
Depending on how the DNA is arranged in the cytosol, we can say that there are two types of cells.
Humans and other animals, all plants, fungi and many microorganisms in nature are composed of eukaryotic cells.
Eukaryotic cells have their genetic material enclosed within a kind of rounded "sac" that we know as core. This is one of the most important characteristics of this type of cells, very useful to differentiate them from prokaryotic cells, for example.
Eukaryotic cells are the units that make up the most complex and incredible organisms in nature; aquatic mammals, trees, fungi, bees, or humans.
There are two large groups of eukaryotic cells: animal cells and plant cells. Although both groups are eukaryotic cells, they present some differences from each other.
Although we can name important differences between the cells of an animal and those of a plant, all eukaryotic cells (with very specific exceptions) share many common characteristics, let's see what they are:
The plasma membrane defines cells and encloses all their internal components, which are "suspended" in the cytosol. The membrane has pores and channels through which some substances can leave the cell and others can enter, which is very important for the communication of the cell with its environment..
In the cytosol are all the components that make a cell have identity and fulfill its functions, that is, there are the nucleus with DNA and other membranous components that are responsible for producing, converting and taking advantage of everything the cell needs to live.
Crossing the internal space of the cell and in close relationship with the plasma membrane, eukaryotic cells have a kind of "skeleton" or "scaffold" inside, formed by filamentous proteins that participate in the transport of materials from a place of the cell to another.
This skeleton gives the cells great physical stability, participates in the movement of the cell body and in the communication between the internal components of the cells and between them and the extracellular environment..
Some eukaryotic cells have structures on their surface that help them to move or move in the space where they are. Such structures, depending on their length and complexity, are known as cilia and flagella..
The cilia look like little hairs that extend from the plasma membrane to no more than 10 micrometers, that is, about a millionth of a meter. We can see them more commonly in microorganisms.
Flagella, on the other hand, are more complex structures that can be up to 1 millimeter long. Many animal and plant cells use these to "swim" quickly in water or in the interior of some tissues..
Eukaryotic cells are distinguished from prokaryotic cells by their complexity and internal organization. In their cytosol, these cells have complex membrane systems that define what scientists call organelles or cytosolic organelles. Common organelles for eukaryotic cells are:
- Nucleus and nucleolus: where deoxyribonucleic acid (DNA) is enclosed in the form of chromosomes. The nucleolus is a region in the nucleus where ribosomes are produced, which are the molecules responsible for translating information from DNA into proteins..
- Endoplasmic reticulum: an organelle formed by an extension of the membrane of the nucleus; in this many proteins are produced whose final destination is the plasma membrane, the membrane or the lumen of other cytosolic organelles.
- Golgi complex: another membranous organelle formed by flattened "sacs" that are stacked together and inside which the proteins produced in the endoplasmic reticulum are modified. Different molecules are distributed from the Golgi complex to different sites in the cell.
- Lysosomes: they are small organelles surrounded by a single membrane. They are full of proteins with the ability to degrade other proteins and molecules that the cell no longer needs, releasing their components to be used by other organelles and / or proteins in the cytosol.
- Peroxisomes: Like lysosomes, peroxisomes are small organelles with simple membranes. Its main function is the degradation of reactive compounds that are harmful to the cell, although they also participate in other important metabolic functions, mainly in the breakdown of fats (although this varies between cell types).
- Transport vesicles: Small vesicles that are “swimming” freely in the cytosol and that transport different molecules inside them; are responsible for "delivering" said molecules to other cell organelles or to the plasma membrane.
- Mitochondria: they are the most important energy centers of cells. They are organelles very similar in size and shape to bacteria (prokaryotic cells). They have their own DNA and from this they produce most of its components. Eukaryotic cells have many mitochondria that are primarily responsible for harnessing oxygen to produce energy.
- Vacuoles: organelles are usually filled with liquid or other substances that often fulfill storage functions.
Animal cells are the cells that make up the organisms belonging to the animal kingdom. They do not have a cell wall, that is, they are covered only by the plasma membrane and can have very variable sizes and shapes.
These cells have all the organelles common to eukaryotic cells: plasma membrane and cytosol, nucleus and nucleolus, endoplasmic reticulum, Golgi complex, mitochondria, lysosomes, peroxisomes, transport vesicles, and, in many cases, vacuoles..
Additionally, animal cells have very small "organelles" known as Centrosomes, that contain the centrioles. Centrosomes are the complexes that are responsible for the synthesis and organization of microtubules during cell division.
Most animal cells have a "runny" or "jelly" layer around them known as glycocalyx which is very important for these and is formed by sugars present in the plasma membrane.
An example of an animal cell is the neuron. Neurons have all the typical organelles of an animal cell and we can identify them thanks to their particular shape, since they have a body or "soma" surrounded by "filaments" formed by the plasma membrane (dendrites) and a known long extension as "axon".
Plant cells are the cells that make up the body of all organisms belonging to the kingdom Plantae. They are distinguished from animal cells by several important aspects:
- Have cellular wall- In addition to the plasma membrane, your cells are covered by a cell wall made up of a special type of compound called cellulose, that provides them with a lot of mechanical and structural resistance.
- They have mitochondria, but they also have other similar organelles called plastids. The most important and characteristic plastid of all plant organisms is known as chloroplast and it is by whom plants can carry out photosynthesis, that is, feed on water and the sun's rays.
- They do not have centrosomes or centrioles for the organization of microtubules during cell division.
- Almost all cells have large vacuoles filled with water, the presence of which is very important for different cellular processes, as well as for maintaining the shape of cells in tissues.
If we see against the light a fragment of the layer of an onion we can see that it is composed of well-defined "cells", one next to the other, almost forming rows and columns; these cells are cells.
Bacteria and archaea belong to a group of organisms made up of prokaryotic cells. These cells, unlike eukaryotic cells, do not have membranes inside and therefore do not have an organelle to enclose and compress their DNA..
Both bacteria and archaea are unicellular organisms, and this is one of the other characteristics that distinguishes eukaryotic cells from prokaryotic cells: that the latter do not form tissues or any kind of multicellular shape..
Prokaryotes are extremely diverse organisms and are of great importance in all ecosystems of the biosphere, where they participate in multiple processes without which life on earth would not be possible..
Like eukaryotic cells, prokaryotic cells also have a membrane cell that shapes them and that contains all its internal components (in the cytosol). Some bacteria also have a Wall that protects them from pathogens, unfavorable environmental conditions, etc..
These cells come in different sizes and shapes: some are rounded and others are rather “rod-shaped”, that is, they resemble a rod. Many of these cells have cilia and flagella that allow them to move from one place to another, either in response to chemical stimuli or due to lack of water..
They do not have any intracellular organelles like that of eukaryotes, but their DNA is more or less restricted to a region of the cytosol known as nucleoid.
Other parts of the prokaryotic cell that are not found in eucatioras are:
Bacteria and archaea are very abundant in nature, but we are usually more familiar with bacteria, as we exploit them from an industrial point of view for various purposes.
Our intestines, for example, are populated with complex bacterial communities that help us digest food and whose imbalance is often what causes colic and diarrhea. The bacteria Escherichia coli is the most common example of intestinal diners.
Industrially speaking, yogurt is produced thanks to the action of two or more species of bacteria of the genus Lactobacillus, that ferment the sugars in cow's milk, producing the characteristic flavor of this food.
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