0:00
Let's begin with the term. The term ento means within. So it refers to a
0:06
membranous system that is within the cell called as endomembranous system. It's a
0:12
complex network of organelles and membranes in eukaryotic cells that works together to produce, modify, package and transport lipids and proteins. In
0:23
eukaryotes, the total surface area of intercellular membrane is about tenfold greater than that of plasma membrane. Many of the organelles inside cells are
0:33
not isolated entities but instead communicate with one another either physically connected by membrane bridges or they are indirectly connected by
0:44
vesicles. Small membrane-enclosed sacs that transport substances between organelles or outside. These interconnected membranes make up the endomembrane
0:57
system. First let us see which are the components of endomembrane system
1:04
Starting with nuclear envelope, then there is endoplasmic reticulum, both rough endoplasmic
1:10
reticulum and smooth endoplasmic reticulum. This is followed by Golgi apparatus, then lysosomes
1:17
vesicles and plasma membrane. Although not technically within the cell, majority of the
1:23
recent studies included plasma membrane in the endomembrane system because as you can see it
1:29
interacts with the other endomembraneous organelles in uptaking substances by endocytosis or releasing
1:36
substances outside of the cell by exocytosis. The endomembrane system does not include the
1:44
membranes of either mitochondrion or chloroplast. Now let us see how these organelles are positioned
1:52
inside the cell for better understanding of endomembrane system. As you see, nuclear envelope
1:59
is surrounding the nucleus that is in continuous connection with rough endoplasmic reticulum
2:05
and smooth endoplasmic reticulum. Endoplasmic reticulum is in close proximity with Colgy
2:14
apparatus. Enzymes or substances are packaged in vesicles to move to different destinations
2:23
or organelles within the cell The lysosome is involved in extracellular digestion and finally plasma membrane is involved in uptaking substances by endocytosis or releasing substances outside of the cell by exocytosis Now let us take a closer look at the
2:45
different parts of the endomembrane system and how they function in the shipping of proteins and lipids
2:53
As you see the outer nuclear membrane is in continuous connection with RER or rough endoplasmic
2:59
reticulum. It's a network of tubes that produce, modifies and transports proteins and other
3:07
molecules throughout the cell. It is often one of the largest organelle that runs throughout the
3:12
cell. As you see this RER has ribosomes studded on its surface involved in the synthesis of
3:18
secretory and membrane proteins. Ribosomes are just like nanomachines that makes proteins
3:24
RER is also the site of protein folding especially the formation of disulfide bonds
3:32
It's also involved in processing like initial glycosylation and also involved in quality control
3:39
That means a misfolded proteins are often degraded in RER called as ER associated degradation
3:47
then SCR is also involved it is also in close proximity with RER it is involved in lipid
3:55
metabolism it synthesizes membrane lipids including phospholipids and cholesterol and also steroid hormones such as estrogen and testosterone. SCR is abundant in liver where it
4:09
detoxifies drugs makes them more soluble and easier to excrete from the body. As you see RER
4:16
is also located near the Golgi apparatus. Vesicles budding off through the RER with
4:24
proteins, modified proteins are received by the Golgi apparatus and sorted and
4:33
packaged at Golgi for delivery to the targeted destination. It is called the
4:38
sorting center of the cell. It is made up of flattened sacks or pouches called
4:45
cisternae. It has three functionally distinct regions. As you see this is a cis phase where
4:52
vesicles from RER is received or fused into the cis phase or it is the reception site
5:02
Then the processing site which is called as the middle site or medial cisternae where modification or glycosylation occurs and then there is trans network where modified proteins are pinched off as vesicles The proteins from the RER
5:19
enters Golg where it is addressed properly tagged. For example, protein that is to
5:26
be targeted to lysosome is tagged with Mano-6-phosphate. Similarly, a different tag for mitochondrial proteins or nuclear proteins etc. If the protein is
5:39
untagged, the default pathway is secreted out of the cell by exocytosis like this
5:47
as you see. If the protein is untagged then from the Golgi apparatus the protein
5:54
is packed inside a vesicle. It pinches off from Golgi apparatus then moves to
6:01
the plasma membrane fuses with the plasma membrane and is released to the
6:06
outside by exocytosis. From Golgi proteins are packed in vesicles and transported to different destinations within the cell or it is secreted out of
6:18
the cell. Here all this shipment occurs through many membranous systems associated with different organelles that makes the endomembrane system. Now let us see how lysosome
6:34
is involved in endomembrane system. Lysosomes are single membrane bound sacks of digestive enzymes
6:41
with relatively acidic pH that breaks down old and damaged cell parts or autophagy also involved
6:49
in extracellular digestion. As you see the genes encoding the digestive protein is transcribed
6:55
into mRNA and ribosomes synthesizes the digestive proteins which moves to the RAR for further protein
7:03
folding and processing then packaged in vesicles and fuses with Golgi further processed and packaged
7:11
and fuses with lysosome. These vesicles fuses with lysosome. Extracellular substances are taken in by
7:20
the cell by endocytosis pinched off from the plasma membrane and now in the cytoplasm as a
7:29
food vacuole or as an endosome that fuses with the lysosome as you see here this lysosome fuses
7:37
with this food vacuole degrading the particles inside and releasing the contents to the cell for further use or excreting the content out of the cell by exocytosis So this is how lysosomes are also
7:57
involved in this endomembrane system for intracellular digestion or extracellular digestion. Let us discuss the functions of endomembrane system. It is essential
8:09
for the proper functioning of eukaryotic cells. It plays a role in a wide variety of cellular
8:15
processes including as you see protein synthesis and modification that happens through RER which
8:23
is a site of synthesis of membrane and secretory proteins. Then protein folding and modification
8:29
takes place in ER oncology apparatus. Then the second function is lipids synthesis and shipment
8:36
of lipids to different destinations. SCR or smooth endoplasmic reticulum is involved
8:42
especially in the synthesis of membrane lipids like phospholipids and cholesterol. The third function is secretion. Proteins and lipids that are destined to be secreted to
8:52
different parts of the cell are packaged into vesicles in Golgi apparatus, properly addressed
8:58
or tagged with chemicals and transported to different locations or to the plasma membrane
9:04
and is secreted out. And the fourth function is endocytosis where plasma membrane is involved
9:11
It can engulf materials from the environment in a process called endocytosis, maybe food or
9:17
pathogens for intracellular digestion. And these materials are transported into the cell by means
9:25
of vesicles. And finally, the system is also involved in detoxification reaction, especially
9:32
SCR is involved in detoxification of drugs and other harmful substances. Let me summarize
9:41
Endomembrane system is a complex network of organelles and membranes in eukaryotic cells
9:48
that works together in tandem to produce, modify, package and transport lipids and proteins
9:56
to different locations within the cell or outside of the cell. Hope you are clear with endomembrane system. Take care. Stay blessed. Thank you so much. You are with biology exams for a dot com
