Le Corps humain : La Cellule - CM#4
Summary
TLDRCe script de vidéo médicale introduit les cellules comme l'unité fondamentale de la vie, qu'elles soient animales, végétales ou bactériennes. Il explique le rôle de la membrane cellulaire, la structure du noyau contenant l'ADN, et la fonction des organites cellulaires tels que les ribosomes, le réticulum endoplasmique, l'appareil de Golgi, les mitochondries et les lysosomes. Le script sensibilise également aux aspects médicaux importants tels que les maladies mitochondriales et prévoit un prochain épisode sur les virus.
Takeaways
- 🎓 La cellule est l'unité fondamentale de la vie, composant tous les organismes, qu'ils soient animaux, végétaux ou bactériens.
- 🌱 Les organismes simples, comme les bactéries, sont composés d'une seule cellule capable de vivre et interagir avec l'environnement.
- 🔬 Les cellules humaines et bactériennes ont beaucoup de points communs, notamment dans la bouche où les bactéries sont plus nombreuses que les êtres humains qui ont jamais existé.
- 🌿 Les plantes sont également composées de nombreuses cellules, qui diffèrent des cellules animales par quelques composants spécifiques.
- 📏 La taille classique d'une cellule est comprise entre 10 et 100 microns, ce qui permet de visualiser la complexité de structure d'un organisme à partir de cellules si petites.
- 🧬 Le corps humain est constitué d'environ 10 000 à 100 000 milliards de cellules, une somme presque impossible à concevoir pour l'être humain.
- 💧 Chaque tissu du corps humain est composé de cellules spécialisées, qui se regroupent pour former des entités avec des activités spécifiques.
- 🧬 Le DNA, contenu dans le noyau de la cellule, est la molécule qui régit le développement et la fonction de chaque cellule, et est spécifique à chaque individu.
- 🔑 Les membranes cellulaires, constituées de phospholipides, sont essentielles pour délimiter le cytoplasme et permettre les échanges moléculaires avec l'extérieur.
- 🌀 Les organites cellulaires comme les ribosomes, les réticulums endoplasmiques, l'appareil de Golgi, les mitochondries et les lysosomes, ont des rôles spécifiques dans la synthèse, le transport, l'énergie et la destruction de molécules au sein de la cellule.
- 🌐 L'importance de la cellule est fondamentale pour comprendre les phénomènes médicaux et biologiques, ainsi que pour préparer l'étude future des cellules virales.
Q & A
Quel est le but du cours de médecine présenté par le Docteur C ?
-Le but du cours est d'expliquer les bases de la biologie cellulaire, en commençant par l'unité fondamentale de la vie, la cellule, pour aider à comprendre de nombreux phénomènes médicaux et biologiques.
Pourquoi le Docteur C considère-t-il que la cellule est importante pour comprendre la médecine ?
-La cellule est la brique de base de tout organisme complexe, et comprendre son fonctionnement est essentiel pour comprendre les phénomènes médicaux et biologiques.
Quel est le niveau de difficulté de la vidéo sur la cellule présentée par le Docteur C ?
-La vidéo est un niveau 2, c'est-à-dire un niveau intermédiaire, conçu pour un public varié sans besoin de connaissances préalables spécifiques.
Combien de types de tissus sont mentionnés dans la vidéo comme composant le corps humain ?
-Trois types de tissus sont mentionnés : le tissu épithélial, le tissu conjonctif, le tissu musculaire et le tissu nerveux.
Quel est le rôle de l'ADN dans la cellule ?
-L'ADN, ou acide désoxyribonucléique, se trouve dans le noyau de la cellule et contient le code génétique qui détermine la structure et la fonction de chaque cellule.
Comment les cellules humaines sont-elles différentes des cellules bactériennes ?
-Les cellules humaines sont plus complexes, composées de plusieurs organites, tandis que les cellules bactériennes sont prokaryotes, sans noyau distinct et avec moins de compartiments spécialisés.
Quel est le rôle des ribosomes dans la cellule ?
-Les ribosomes sont les usines de production de protéines. Ils lisent le message codé de l'ARN messager et assemblent les acides aminés pour former des protéines.
Quel est le rôle du réticulum endoplasmique dans la cellule ?
-Le réticulum endoplasmique est un réseau de membranes à l'intérieur de la cellule qui est impliqué dans la synthèse de lipides, la production de certaines hormones et la dégradation de toxines.
Quel est le rôle de l'appareil de Golgi dans la cellule ?
-L'appareil de Golgi sert de centre postal dans la cellule, recevant des protéines et des molécules成熟s du réticulum endoplasmique et les préparant pour être envoyées à d'autres parties de la cellule ou libérées à l'extérieur.
Comment les mitochondries sont-elles impliquées dans la production d'énergie au sein de la cellule ?
-Les mitochondries sont les usines d'énergie de la cellule, utilisant l'oxygène et des molécules telles que le glucose pour produire de l'ATP, la monnaie énergétique universelle des organismes vivants.
Quel est le rôle des lysosomes dans la cellule ?
-Les lysosomes sont des organites qui contiennent des enzymes acides et sont chargés de décomposer les protéines et d'autres molécules pour recycler les composants et les réutiliser dans la cellule.
Outlines
🌱 Introduction à la cellule : Unité fondamentale de la vie
Le docteur C accueille les téléspectateurs dans sa classe de médecine et présente la nouvelle capsule vidéo. Il remercie les abonnés et explique que le sujet de cette vidéo est la cellule, qui est la brique de base de tout organisme complexe. Il souligne l'importance de comprendre la cellule pour saisir les phénomènes médicaux et biologiques. Le docteur C propose une introduction à la cellule, ses composantes et sa structure, en abordant le niveau intermédiaire des explications. Il insiste sur la variété des cellules au sein du corps humain et sur le fait que chaque tissu est formé de cellules spécialisées. La vidéo se veut accessible à tous, sans limite d'âge ou de formation scientifique préalable.
🛡️ La membrane cellulaire et son importance
Cette partie du script se concentre sur la structure et la fonction de la membrane cellulaire, qui est composée de couches doubles de phospholipides. Le docteur C explique comment ces molécules se répartissent naturellement en couches pour former une barrière hydrophobe et hydrophile. Il détaille également le rôle des protéines traversant la membrane, qui permettent des échanges moléculaires essentiels avec l'extérieur de la cellule. Le paragraphe couvre également la structure du noyau cellulaire, composé d'une enveloppe double perforée de pores, et l'importance de l'ADN qu'il abrite, qui est compacté en chromosomes pour être stocké efficacement dans un espace restreint.
🧬 La production de protéines et le rôle des organites cellulaires
Le script aborde le processus de synthèse des protéines, qui sont essentielles à la vie cellulaire. Il décrit le rôle des ribosomes, organites cellulaires chargés de la traduction du messagerie ARN en chaînes d'acides aminés pour former des protéines. Le docteur C explique également le fonctionnement des deux types de réticulum endoplasmique, lisse et rugueux, dans la production et la maturation des protéines. Il mentionne le rôle du Golgi dans le traitement final des protéines avant leur exportation hors de la cellule, soulignant l'importance de ces organites dans la production et la distribution des protéines nécessaires au fonctionnement de l'organisme.
🔋 Les mitochondries et le lysosome : Énergie et destruction cellulaire
Dans cette partie, le docteur C explore le rôle des mitochondries comme sources d'énergie au sein de la cellule, en consommant de l'oxygène et du glucose pour produire de l'ATP. Il mentionne que les mitochondries possèdent leur propre ADN et sont transmis uniquement par la mère. Il décrit également le lysosome comme un organite de destruction, qui contient un environnement acide et est chargé de décomposer des molécules, y compris les protéines, pour libérer des briques élémentaires réutilisables. Le script conclut en soulignant l'importance de ces organites dans la santé et la fonction des cellules, et annonce un prochain épisode sur les virus.
Mindmap
Keywords
💡Cellule
💡Tissu
💡Membranes cellulaires
💡Noyahud
💡ADN (Acide désoxyribonucléique)
💡ARNm (ARN messager)
💡Ribosomes
💡Réticulum endoplasmique
💡Appareil de Golgi
💡Mitochondrie
💡Lysosome
Highlights
La cellule est l'unité fondamentale de la vie, composant tous les organismes complexes et simples.
Le nombre de cellules dans le corps humain est d'environ 10 000 à 100 000 milliards.
Les cellules humaines et bactériennes ont beaucoup en commun, y compris la capacité de vivre et d'interagir avec l'environnement.
Les cellules végétales diffèrent des cellules animales par quelques composants spécifiques.
La taille classique d'une cellule est de 10 à 100 microns, équivalent à 1 millimètre pour 10 cellules alignées.
Les différentes tissus du corps humain sont composés de cellules spécialisées.
Le développement des tissus est régi par l'ADN, la molécule célèbre trouvée dans les cellules.
Il existe quatre types principaux de tissus dans le corps humain : tissu épithélial, tissu conjonctif, tissu musculaire et tissu nerveux.
La membrane cellulaire est composée de couches doubles de phospholipides, avec des propriétés hydrophobes et hydrophiles.
La membrane cellulaire contient des protéines qui facilitent les échanges moléculaires avec l'extérieur de la cellule.
Le noyau cellulaire est l'organite le plus important, contenant l'ADN et entouré d'une double membrane.
L'ADN est composé de 4 bases différentes, formant des paires de bases qui déterminent le code génétique.
Les ribosomes sont les usines de production des protéines, lisant l'ARN messager et assemblant les acides aminés.
L'appareil de Golgi sert de centre postal, achevant la maturation des protéines et les expédiant hors de la cellule.
Les mitochondries sont la source d'énergie de la cellule, produisant de l'ATP à partir de l'oxygène et du glucose.
Les lysosomes sont les organites de destruction de la cellule, décomposant les protéines et d'autres molécules.
La compréhension de la cellule humaine est fondamentale pour comprendre les cellules bactériennes, végétales et virales.
Transcripts
Hi there, welcome to my class.
I'm Doctor C, and here's a new Medicine Capsule.
By the time I'm shooting this video you're already over 50 subscribers in my class,
it's starting to get a little daunting.
Can you hear me there in the background? This video is subtitled, as always
, to facilitate the understanding of people who want it, or who
need it.
It is also chaptered, to facilitate its viewing, or re-viewing.
Today, we are attacking the fundamental unit of life, whether animal,
vegetable or bacterial.
The cell.
Why an episode on the cell? Quite simply because the cell is the first
brick of any complex organism, and it is therefore devilishly important to understand in
order to understand many medical and biological phenomena.
Hold on tight, we're off for a 20-minute capsule.
Time for me to get to the board, here is a little introduction first.
This video is level 2, that is to say the intermediate level of explanations
that you will find on this channel.
It is for you, whoever you are, whatever your training, your age or
your knowledge of the subject.
No age limit, or need to have followed scientific studies here, everyone
is welcome on this video.
The explanations are however more advanced than on the level 1 videos, and you
may need to review this video calmly afterwards to
understand all the subtleties.
My mission for the day? Maintain the flame of your curiosity.
Ready ? Let's go for the medical capsule!
The cell represents the basic unit of life.
Most living organisms are made up of only one cell.
Complex organisms are composed of an assembly of many cells, and
simpler organisms, such as bacteria for example, are composed of
only one cell.
And yet, bacteria are quite capable of living, of moving, of interacting with
their environment.
Bacterial cells have a lot in common with human cells.
Do you know that just in your mouth, there are more bacteria than there
have ever been human beings on earth since man has existed? Can you imagine
the overcrowding?
Plants are also composed of a considerable number of cells.
These are plant cells, which differ from animal cells
in only a few components, which we will discuss in more advanced videos on the subject.
The classic cell measures between 10 and 100 microns.
A micron represents one thousandth of a millimetre.
If we align 10 cells next to each other, we therefore arrive at about 1
millimeter.
It is therefore necessary to align 100 cells to form 1 centimeter.
The human body is made up of a cluster of cells.
There are, on average, between 10,000 and 100,000 billion.
Can you imagine what that means? Well no, neither do I.
It is almost impossible for a human being to represent such a sum,
comparing it to other known values.
If we compare this figure to the number of human beings living on the planet, we are
more than 100,000 times more.
And yet, this population of cells acts and interacts to form the complex being
that we represent.
Every tissue in the human body is made up of cells.
The skin ? Special cells.
The inner ear? Special cells.
Lungs ? Special cells.
A hair ? Special cells.
The teeth ? Special cells.
White blood cells? Special cells.
The cells then group together into tissues, which form entities that have specific activities
.
These cells have a common embryological origin.
Tissue development fits together, and it's all managed by the famous molecule
found in cells, DNA.
The tissues are all different, and they differ in the cells of which they are composed, the organization
and the form of these cells.
There are broadly 4 types of tissues in the human body.
Epithelial tissue is the tissue that covers the surfaces of the body, and which covers the
inner lining of hollow organs.
It is generally very thin.
Connective tissue is the supporting tissue, which aims to protect and support
the organs.
Bone tissue and blood are part of connective tissue.
Finally, there is also muscle tissue, and nervous tissue, which we will discuss
in future videos.
In this presentation, we will tackle the human cell in general,
without addressing the specificities of the tissues.
Once these notions are well integrated, we will be able to attack, in more advanced videos,
the cellular specificities of each organ, which make the human being that you are,
this great almost magical machine that is watching this video.
Every cell, whatever it is, is surrounded by a membrane.
This membrane, which may seem inert at first glance, is in fact one of
the most important and exciting parts of the cell.
The membrane delimits the cytoplasm, that is to say the liquid portion of the cell, in which
the various cellular organelles float.
The membrane is composed of a double layer of phospholipids.
A phospholipid, which is conventionally represented as in this image, is a molecule composed
of a head, which dissolves in water, and two extensions, which dissolve
in oil.
Have you ever tried mixing water and oil? If by shaking
well, we obtain a cloudy mixture which seems homogeneous, we will notice that the molecules
will very quickly come together, between the oil and the water.
As you can see on this little animation, the drops of oil will prefer to
assemble together, rather than mixing with the water.
This is due to their physical properties, which cause oil molecules to not
mix with water molecules.
At the level of the membrane, the same thing happens.
The molecules of phospholipids will naturally assemble together, to form a double
layer.
The external part and the internal part of the membrane are composed of the heads of the
phospholipids, which are in contact with the liquid in which the cells are bathed.
The interior of the membrane is made up of the lipid arms of the phospholipids, which
come together to form a fatty layer, as you can see in this image.
When we therefore cross the membrane of a cell, whether from the inside towards
the outside of the cell, or in the opposite direction, we arrive in front of a layer which is hydrophilic,
or which “likes water”, then inside, there is a fatty layer, composed of
lipids, which is called hydrophobic, or "which does not like water", and finally,
there is a hydrophilic layer, before leaving the membrane .
These bonds between hydrophilic portions and hydrophobic portions make it possible to maintain
a certain fluidity in the membrane.
A cell membrane is indeed not rigid and impermeable, because it needs
to exchange molecules with its exterior.
This is made possible thanks to the cohesion between the hydrophilic and hydrophobic parts
of the membrane phospholipids.
The cell membrane is also crossed by many proteins, which allow
interactions between the interior and exterior of the cell.
Some proteins are specific, and allow
certain molecules
to be caught in the extracellular fluid . Some still play the role of receptors, and send signals inside
the cell, when specific molecules are recognized outside.
Others make it possible to exchange sodium and potassium ions between the inside and
the outside of the cell.
The study of all these transporters is beyond the scope of this video, but keep
this in mind, because it will be useful in other videos, for example on the transmission
of information between two neurons.
The nucleus is probably the most important organelle in the cell, and also
the easiest to spot under an electron microscope.
It is composed of a double membrane, which is called the nuclear envelope.
Each membrane is made up of a double layer of phospholipids, like the membrane
that surrounds the cell.
There are therefore 4 layers of phospholipids that surround the nucleus of the cell.
This membrane has the particularity of being pierced with pores.
These pores are surrounded by molecules, which regulate the passage of proteins and other
substances between the nucleus and the cell.
We don't go like that from the cellular cytoplasm inside the nucleus of the cell.
It's a secure area, and you'll quickly understand why.
The DNA, or Deoxyribonucleic Acid, is found in the nucleus.
Indeed, in each cell, there is a copy of this DNA.
DNA, so complex and so specific to each human being, is however
only composed of 4 different molecules, assembled in a particular order.
They are called the bases.
These are adenine, thymine, guanine and cytosine.
The DNA molecule is made up of billions of base pairs that come together in
an order specific to each individual.
Its total length, if you unfold it completely, exceeds one meter.
Do you see the problem coming? Fit a molecule more than a meter in length
into a cell nucleus, which measures a hundredth of a millimeter?
To do this, the genetic code is partially folded, linked to proteins, which allow it
to be compacted.
Sort of like organizing your computer, if you will.
If you had billions of files placed in a precise order, but in bulk on your
desktop, you would have a very hard time finding a particular file.
On the other hand, if you store these files in folders, then these folders in other
folders, and so on until you only have a few folders, the organization
would be greatly simplified, without losing the initial order. files.
And finally, if you want to make a copy of these files, you're probably going to want to
form a compressed folder.
It will be smaller, and easier to copy.
At the cellular level, this is called a chromosome.
In order to be used, the DNA must be unfolded.
It is then mixed with proteins.
This mixture is called chromatin.
This unfolded DNA is then copied by specific proteins to form
messenger RNAs, which then leave the cell nucleus through the pores of the
nuclear double membrane.
When DNA is copied, does it turn into RNA?
Indeed, this name change is simply due to a molecular change, between DNA
and RNA.
RNA is made up of slightly different, and much less stable, molecules than
DNA.
The purpose of RNA is very transient anyway, and it will be quickly degraded
once its activity is done.
One of the 4 bases is also modified in this molecule, thymine is replaced
by uracil in the code used.
What will this RNA be used for? We discuss it right after, in the part of the video that talks about
the ribosome.
The nucleus also contains organelles, which are called nucleoli.
These organelles are responsible for the production of ribosomes, another organelle of the cell,
which aims to synthesize proteins.
The human body uses 20 different amino acids.
These amino acids are like building blocks, and the order of their
assembly determines a structure called protein.
A protein is therefore an assembly of amino acids, in a very specific order.
This precise order gives it a three-dimensional structure, and a particular action.
Amino acids are brought to the body in three ways.
Some are created naturally by the body from simple molecules, others
are provided by the breakdown of proteins already present in the body, which are
broken down into small basic amino acids.
Finally, others are brought in by food and destroyed by cellular organelles
called lysosomes, to provide the body with building blocks.
The ribosome is, in a way, the manufacturing plant for these proteins.
Ribosomes are cell organelles formed from two subunits, which are created
in the nucleolus, a part of the cell nucleus.
The ribosome picks up messenger RNA fragments that are generated in the nucleus by
proteins that read DNA.
These messenger RNA fragments leave the nucleus through the nuclear pores, and then find themselves
close to the ribosomes, which pick them up to transcribe them.
By reading the genetic code, ribosomes finally assemble proteins from
amino acids that circulate freely in the cytoplasm, the cellular fluid.
This synthesis makes it possible to create all the molecules necessary for life.
You can see on this diagram the interpretation of the genetic code which is made by the ribosome.
The letters ATCG represent the 4 bases that make up DNA.
Their particular combination is read by the ribosome, which deduces which amino acid
to use for the formation of the protein.
When the ribosome reads a STOP combination (arrow on screen), it detaches the
primary protein , which is thus formed.
Cells that are major protein producers, those that synthesize
insulin for example, have many ribosomes than others.
Again, within the cell, cellular function strongly influences the content
of the cytoplasm.
The endoplasmic reticulum constitutes a network of membranes inside the cell.
These membranes form cisterns, the contents of which are not in contact with the interior
of the cell.
On the other hand, the interior of these membranes is in contact with the zone situated between
the two layers of the double membrane of the core.
In the cell, therefore, there are networks of membranes whose content is in some
way independent of the composition of the cellular cytoplasm.
There are two types of endoplasmic reticulums; the smooth and the rough.
This name actually comes from the appearance of these membranes under an electron microscope.
When the endoplasmic reticulum is covered with ribosomes on its surface, it has a
visually rough appearance, and takes its name from it.
The smooth endoplasmic reticulum contains many enzymes, molecules that
are used for the production of certain fats, certain hormones.
It also plays a role in the digestion and breakdown of certain toxins, such as
drugs or alcohol.
The rough endoplasmic reticulum is composed of a network of membranes similar to the smooth endoplasmic
reticulum, but on which are attached ribosomes, which are responsible
for the formation of proteins.
Once the primary proteins formed by the ribosomes, they are sent
to the rough endoplasmic reticulum, and it is there that these proteins will
change, take their final form, and become mature.
Once this maturation is complete, the small vesicles from the rough endoplasmic reticulum
are sent to the Golgi apparatus.
The Golgi apparatus bears the name of its discoverer, Camillo Golgi, who described it
in 1898.
It has a role as a postal center in the human cell.
Under the microscope, it looks like the smooth endoplasmic reticulum, but it has a very
different function.
Roughly, it can be compared to a carrier.
It receives proteins and molecules that have matured in the rough endoplasmic reticulum
, refines them, and then sends them out into circulation.
This apparatus is highly developed in certain cells whose role is to secrete
substances, such as cells which secrete hormones, for example.
Once the molecules are ready to be sent, small vesicles detach from the
Golgi apparatus, and will fuse with the cell membrane.
The products that were in the vesicles are thus released outside
the cell, where they will be able to produce their action, either directly or by passing
into the bloodstream (link).
The mitochondria is the nuclear powerhouse of your cell.
Or the wind turbine if you prefer.
In short, it is within it that the production of energy occurs.
The mitochondrion has the particularity of being an independent organelle inside
the cell.
It has its own DNA, multiplies on its own, independently of the cell,
and is also transmitted to children only by the mother.
The sperm not having mitochondria, the mitochondria of children are those
that were present in the egg, and therefore provided by the mother.
The mitochondrial DNA found in an individual is therefore always that of his
mother.
This has a medical interest when a member of the couple has a mitochondrial disease.
If it's the father who has it, he gets it from his mother, but above all, he
can't pass it on to his children.
The role of mitochondria is to produce fuel for the body.
For this, the mitochondria consumes oxygen, which is provided by red blood cells,
as well as glucose or other molecules, to create a molecule called
ATP, for Adenosine TriPhosphates, which is the universal energy currency of living organisms
.
The number of mitochondria is variable in cells, depending on their activity.
A muscle cell indeed has many more mitochondria than a lung cell,
because it must produce much more energy to the tissues.
We will cover this energy metabolism later in more advanced videos
on the subject.
The lysosome is a bit like the destruction of the cell.
It is an organelle also surrounded by a membrane, inside which
there is an acidic environment.
To maintain this environment, the lysosome membrane contains many proteins
that bring acid inside the organelle.
The role of the lysosome is to transform molecules, destroy them, and release
the molecules that compose it.
They have a somewhat opposite role to that of ribosomes, which produce proteins
from the body's amino acids.
Here, they destroy the proteins to release the amino acids, the small bricks
which are thus found free, and usable for the production of new proteins.
If you want a metaphor that works on the lysosome, imagine an employee whose
role is to destroy houses, and then supply you with the bricks individually,
so that you can build something else using this same material.
Lysosomes are also widely used in white blood cells because they
destroy cells and waste that are
ingested by defense cells.
All this obviously seems quite theoretical, but it is an essential basis for the functioning
of any organism.
Understanding the human cell will allow you to understand the bacterial cell, the
plant cell, but also the viral cell.
Next week, I'll show you a news video, because we'll be talking about
viruses! Did you like this video ? Want
to see more? So my mission is fulfilled for today!
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