The more you seek, the more you find. Well, this
is perhaps the truest statement when it comes to biology. In 1665, Robert Hooke discovered,
using a microscope, that corks had tiny pore-like structures within them. He named
these pores ‘cells’. The word “Cell” derives from the latin word Cella, which means a simple
room. Even though Hooke discovered the cell, he was not able to get a complete understanding
of what cells were or what their function was. Fast forward to 1838, when the cell theory
was first proposed by Matthias Schleiden and Theodor Schwann. The theory stated
that both plants and animals are made up or are a product of cells, and that these
cells also contain a nucleus within them. Unfortunately, the star of our video, the
Endoplasmic Reticulum remained unknown until 1897, when a french cytologist, Charles Garnier
first gave it some much-needed attention. Garnier termed this new found structure as
‘ergastoplasm’. Yeah. Not a cute name. Sounds like a nasty infection, doesn’t it? Fortunately,
the ER only had to live with this name for five whole decades. But in 1953, Keith Porter
renamed the organelle Endoplasmic Reticulum. The term reticulum was added to describe the tubular
network visualized under an electron microscope. After decades of study on the ER, which
is short for Endoplasmic Reticulum, we now have a deeper understanding of what it
is, and what its functions are within the cell. It took more than 350 years for humans to discover
and understand some of this organelle’s basic functions, but the process of fully realizing
the potential of the ER is still underway. Perhaps, it could be you who discovers
that the ER has some unknown function that could hold the secret gateway to
eternal life. But before all of that, first, let me introduce you to the structure
and function of the Endoplasmic Reticulum. The Endoplasmic Reticulum is the cell organelle
that produces, processes, and secretes proteins. This organelle is found in almost every
cell in humans, and other animals, and plants. The function of
the endoplasmic reticulum is not limited just to protein synthesis. The
Endoplasmic Reticulum also acts as a storage site for calcium and is an essential component
in the production of lipids and steroids. But what does the Endoplasmic Reticulum look like? As the popular saying goes: form follows function. The endoplasmic reticulum has a structure
designed to enable it to efficiently carry out its functions. And of all the eukaryotic
organelles, the Endoplasmic Reticulum has the most architecturally striking structure, let
me tell you. Once you know what the Endoplasmic Reticulum looks like, you will never be able
to miss it under a microscope or on a textbook. If we look at the structure of the Endoplasmic
Reticulum it basically looks like a bunch of ‘rough sheets and smooth tubules’. It kinda sounds
like a racy movie name, right? But I digress. The ER is a network of interconnected
flattened sheets, known as cisternae, and branching tubules that extend from the nucleus
to the rest of the cell. These sheets and tubules are made of a phospholipid membrane, continuous
with the membrane that surrounds the nucleus, and yeah, similar to the membrane
that you find surrounding the entire cell. This network of tubules is held in
place with the help of the cytoskeleton. In terms of morphology, the Endoplasmic Reticulum
can be classified as rough endoplasmic reticulum, and smooth endoplasmic reticulum. We call it
rough endoplasmic reticulum because if we look at the surface of the rough ER we notice
the presence of membrane-bound ribosomes; whereas in smooth ER we do not
find any membrane-bound ribosomes. The rough endoplasmic reticulum accounts for 60% of the endoplasmic reticulum, while
the remaining 40% is smooth ER. Before we talk separately more about rough
endoplasmic reticulum and smooth endoplasmic reticulum, I believe we should turn the
spotlight to ribosomes for just a moment. So ribosomes are complex molecules where protein
synthesis or translation occurs. They are little factories, let’s say. Every ribosome has
two subunits, a larger and a smaller subunit. These subunits contain ribosomal RNA molecules and
proteins which are essential for mRNA translation. Remember mRNA translation is one of
the final steps in the conversion of the information that you have
in your DNA to an actual protein. Now we’re going to focus on the rough
endoplasmic reticulum for a moment. The lumen of the rough endoplasmic reticulum
is slightly smaller in width than the lumen of the smooth endoplasmic reticulum. The lumen
is the space we find between the membrane walls of the endoplasmic reticulum sheets
and tubules. So the lumen of the rough ER is 20 to 30 nm wide, whereas the lumen of
the smooth ER is about 30 to 60 nm in width. The rough endoplasmic reticulum plays a central
role in protein synthesis. It is where proteins are synthesized, modified, transformed, and
finally released. Protein synthesis begins with the translation of mRNA by ribosomes attached
to the rough endoplasmic reticulum membranes. These proteins go on to be a part of the
cell membrane or are transported out of the cell to other destinations. Proteins
are essential for many physiological processes within the cell such as cell signaling,
DNA synthesis and repair, transport of molecules, forming cellular structure, and I could go on
and on. Without the rough endoplasmic reticulum, there would be no proteins, and without
proteins, the cell would not be able to survive. Hell, we would not be able to
survive. So you now know why we need to devote some attention to
the endoplasmic reticulum, right? Unlike the rough endoplasmic reticulum,
which is located close to the nucleus, the smooth endoplasmic reticulum is
mainly located near the cell periphery. Although the smooth endoplasmic reticulum
has no ribosomes attached to it, its structure is more complex than that
of the rough endoplasmic reticulum. Membranes lining the smooth ER follow a
tortuous course, and are irregular in size. The smooth endoplasmic reticulum has many
functions including synthesis of lipids, steroids, carbohydrates as well as the metabolism
of exogenous substances, such as drugs or toxins. The functions of the smooth ER vary depending
on the type of cell. The smooth endoplasmic reticulum found in muscle cells has a special
name. It is called the sarcoplasmic reticulum, which regulates calcium ion concentrations
during muscle contraction and relaxation. In the adrenal glands, the smooth
endoplasmic reticulum secretes cholesterol which is a precursor
of steroid hormones. In the liver, the smooth endoplasmic reticulum synthesizes
and stores enzymes essential for detoxification, essentially it helps you get rid of things that
are bad for your body, like alcohol and drugs. Now we’ve reached the end of the tutorial. Click
on the next video to continue learning. And don’t forget to like this video if you want to tell
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