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The cell
Transcription proposée par Anne-Cécile Auclair
Attention , cette transcription a été réalisée à partir de l’écoute du DVD, il peut arriver que
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On the dissected world of biology program 2, it’s time to investigate your inner real estate : your
cells.
We’re made up of up to seventy-five trillion cells. We’ve only got time to explore one of them. But
don’t worry, you’ll know everything about the average cell by the time we’re through, plus we’ll
get you up to speed on the mysteries of DNA, and crack the genetic code inside each and every one
of us.
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Section B.
Okay! It’s time to discuss the different parts of the cell, the structures within the cell allows to
perform different tasks, which are vital to its life. Each part of the cell performs a different but
crucial function.
And, most importantly, you need to realize that the development of any organism, including a cell,
is driven by its function. So every structure in the cell looks as it does because that structure
provides a very specific function.
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This is a eukaryotic cell and this is the nucleus.
The nucleus is kind of the brain of the cell. It’s the genetic headquarter. This is where DNA, in the
form of chromosomes, hangs out. Some of the DNA in the nucleus is very dense and forms a region
called the nucleolus.
RNA, which are temporary copies of the DNA, are also made in the nucleus.
Chromosomes are like the text book of who you are. They hold your genetic information. They also
coordinate the activities of the cell, kind of like the cell’s very own personal system.
[........]
Here is a footage of a real cell. These thread-like structures are the chromosomes. As we said, these
chromosomes contain all of your genetic information in the form of genes and, more importantly,
DNA. Chromosomes are only visible when a cell is about to split during mitosis, as you see here.
We’ll get much more into this later on.
Now for the other parts of the cell.
Cytoplasm is the cell fluid found between the cell membrane and the nuclear envelop. The
organelles of the cell are found within the cytoplasm and, as we said, are like the small organs of
the cell.
The endoplasmic reticulum, or ER, is a maze of canals within the cell.
The ER takes up about half the membrane of the cell.
Anne-Cécile Auclair – Emilangues - 2011
The ER is involved with protein synthesis, or creation, modification and transport. The protein
found in the cell membrane is made in the ER, and we all know how important protein is.
The fluid inside the ER is called cisternal fluid. And the fluid everywhere else in the cell, as you
know, is called the cytoplasm.
There are two types of endoplasmic reticulum in the cell, either rough or smooth. Each is
responsible for different things. Rough, or RER, means it contains ribosomes, which are large
bunches of proteins and RNA, that we’ll tell you about much later. RER is responsible for creating
proteins. Smooth, or SER, means it doesn’t contain ribosomes. Its function is to process lipids,
including fats and steroids.
The ribosomes function as the site of protein synthesis, in either the cytoplasm or on the rough ER.
You’ll hear more about ribosomes later, they’re very important.
Now, this thing that looks like a stack of pancakes, is the Golgi apparatus. The Golgi apparatus is
kind of like a temporary warehouse, processing facility, and shipping site for the ER.
Proteins from the rough ER merge with the Golgi apparatus. Here, the proteins can be stored,
processed, and then shipped to the parts of the cell that need them. Each pancake, if you will, is
responsible for a different stage of protein processing. The Golgi apparatus is kind of like the postoffice of the cell.
Lysosomes store digestive enzymes that are made in the rough ER. Lysosomes digest the cell’s
food and wastes. When they’re abnormal, they cause fatal childhood diseases.
You can think of the lysosomes as the recyclers of the cell. They take proteins and break them up
into amino acids so they can be used again.
Mitochondria are like the cell’s power plant. They perform the function of cellular respiration,
which we will discuss in more details later on in the video.
In short, respiration is the process of breaking up the covalent bonds in glucose for energy, using
enzymes which are found in the membranes of the mitochondria. These membranes are folded,
giving the mitochondria more surface area to synthesize more ATP.
The mitochondria also have their own DNA, as this. They are self-replicating organelles, making
some of their proteins with their own DNA genetic code. So mitochondria keep making more of
themselves. All mitochondria came from some previous mitochondria.
Chloroplasts are found only in plant cells. And they also have their own DNA that helps direct
their functions, one of which is photosynthesis. Now we’ll come back to photosynthesis later too,
but for now, just know that photosynthesis is the process that converts light energy into a form of
energy that plants and animals can use. You should know that, just like the mitochondria, the folds
give the chloroplasts more room to work with or more surface area.
Now back to animal cells:
Then there’s the cytoskeleton, and, just like your own skeleton, it gives the cell its shape.
The plasma, or cell membrane is the cell’s outer shell. It’s also called the phospholipid bilayer,
because it’s made of two layers of molecules, which are made of phosphorous and fatty molecules.
Hence, phospho for phosphorous, lipid for fat, and bilayer for two layers.
Now we’re going to revisit the plasma membrane later. For now, just know that this plasma
membrane encloses the cell, is made of phospholipids, and allows things in and out of the cell
selectively.
Okay, and now you know what cells are and how they look.
They are the building blocks of you. Any part of your body that you look at, there is a cell there.
Anne-Cécile Auclair – Emilangues - 2011