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By the end of this section, you will be able to:
  • List the components of the endomembrane system
  • Recognize the relationship between the endomembrane system and its functions

The endomembrane system (endo = “within”) is a group of membranes and organelles ( [link] ) in eukaryotic cells that works together to modify, package, and transport lipids and proteins. It includes the nuclear envelope, lysosomes, and vesicles, which we’ve already mentioned, and the endoplasmic reticulum and Golgi apparatus, which we will cover shortly. Although not technically within the cell, the plasma membrane is included in the endomembrane system because, as you will see, it interacts with the other endomembranous organelles. The endomembrane system does not include the membranes of either mitochondria or chloroplasts.

Art connection

The left part of this figure shows the rough ER with an integral membrane protein embedded in it. The part of the protein facing the inside of the ER has a carbohydrate attached to it. The protein is shown leaving the ER in a vesicle that fuses with the cis side of the Golgi apparatus. The Golgi apparatus consists of several layers of membranes, called cisternae. As the protein passes through the cisternae, it is further modified by the addition of more carbohydrates. Eventually, it leaves the trans face of the Golgi in a vesicle. The vesicle fuses with the cell membrane so that the carbohydrate that was on the inside of the vesicle now faces the outside of the membrane. At the same time, the contents of the vesicle are ejected from the cell.
"Membrane and secretory proteins are synthesized in the rough endoplasmic reticulum (RER). The RER also sometimes modifies proteins. In this illustration, a (green) integral membrane protein in the ER is modified by attachment of a (purple) carbohydrate. Vesicles with the integral protein bud from the ER and fuse with the cis face of the Golgi apparatus. As the protein passes along the Golgi’s cisternae, it is further modified by the addition of more carbohydrates. After its synthesis is complete, it exits as integral membrane protein of the vesicle that bud from the Golgi’s trans face and when the vesicle fuses with the cell membrane the protein becomes integral portion of that cell membrane. (credit: modification of work by Magnus Manske)

If a peripheral membrane protein were synthesized in the lumen (inside) of the ER, would it end up on the inside or outside of the plasma membrane?

The endoplasmic reticulum

The endoplasmic reticulum (ER)    ( [link] ) is a series of interconnected membranous sacs and tubules that collectively modifies proteins and synthesizes lipids. However, these two functions are performed in separate areas of the ER: the rough ER and the smooth ER, respectively.

The hollow portion of the ER tubules is called the lumen or cisternal space. The membrane of the ER, which is a phospholipid bilayer embedded with proteins, is continuous with the nuclear envelope.

Rough er

The rough endoplasmic reticulum (RER)    is so named because the ribosomes attached to its cytoplasmic surface give it a studded appearance when viewed through an electron microscope ( [link] ).

In this transmission electron micrograph, the nucleus is the most prominent feature. The nucleolus is a circular, dark region inside the nucleus. A nuclear pore can be seen in the nuclear envelope that surrounds the nucleus. The rough endoplasmic reticulum surrounds the nucleus, appearing as many layers of membranes. A mitochondrion sits between the layers of the ER membrane.
This transmission electron micrograph shows the rough endoplasmic reticulum and other organelles in a pancreatic cell. (credit: modification of work by Louisa Howard)

Ribosomes transfer their newly synthesized proteins into the lumen of the RER where they undergo structural modifications, such as folding or the acquisition of side chains. These modified proteins will be incorporated into cellular membranes—the membrane of the ER or those of other organelles—or secreted from the cell (such as protein hormones, enzymes). The RER also makes phospholipids for cellular membranes.

If the phospholipids or modified proteins are not destined to stay in the RER, they will reach their destinations via transport vesicles that bud from the RER’s membrane ( [link] ).

Questions & Answers

what is money
Lawal Reply
what is supply
Lawal
the total number of goods present at a particular area at a particular time
Offset
the meaning of elasticity
Affum Reply
how to knw the break even point in business
Edmore Reply
hello
Marshal
hello
ghulam
hi
Kakay
hi
Ornill
hi
Bakari
Good evening
owi
when TOTAL COST & TOTAL REVENUE equal each other that's break even point
Bappy
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Kakay
yaah
Chris
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Kakay
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Amarachi
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Marshal
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Noah
Hey
Andile
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Offset
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Offset
what are the importance of economics
sani Reply
hello
Marshal
welcome
Zaid
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Kakay
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Mona
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Bakari
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Mona
where are you from?
Bakari
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Amarachi
what is development?
juwel Reply
it shows how many products customers are willing to purchase as the price of those product increase or decrease
Asha Reply
economics as a science
skima Reply
What is utility
Jimoh Reply
utility is a total satisfaction derives from a consumer.
Umar
what is ranking reveal choices?
Umar
wants satisfying power of a commodity is known as utility........
SHADAB
What is elasity
bohvy
Differentiate between scarcity and choice and explain how they effect perfectly elasiticity of demand and give relevant example with type of goods affected
PATRICK
Utility is ability if of available goods to satisfy human wants
PATRICK
any idea about equilibrium?
Umar
equilibrium where price and quantity demanded equals
Bappy
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john
Equilibrium is when quantity demanded of goods and services is equal to supply to the market.
john
saaa.....
Bright
how about the profit....anybody can explain
Jeff
how about equilibrium of consumer?
Umar
bappy,john thank you the answers.
Umar
Utility Simply means the satisfaction a consumer derives from consuming a good or service
Hez
Pls can someone explain Elasticity of demand in a short terms
Osuayan
it's a degree of responsiveness to demand due to changes in prices
Ukpen
what is scarcity? pls help
Mikateko Reply
scarity is when there is a huge demand for certain goods and services but there's limited resources to actually produce those things
Mario
thank you
Kakay
what is development?
juwel
what is distribution
umar Reply
1.what is distribution? 2.what are factors affecting distribution? 3.releat what you are writing in the contest of economics and Nigeria situation
umar
what is demand
Obianyido Reply
things that are needed or wanted
Mario
The market for you In Ilorin has the following demand and supply equation Qd + 5p =9520 Qs =2.5p - 125 a) determine the equation price and quantity b) Explain the situation when the market price is below the equlibrum price
Rasheee Reply
solutions
Alex
What is scale of preference
Richmond Reply
Pls what is scale of preference
Richmond
scale of preference is a arrangement of individual wants in order of priority
Lamina
the arrangement of people want inoder of demand
Ada
explain whether decisions in microeconomics involve an opportunity cost
Sonali Reply
What is primary activity
Yeboah Reply
indigenization is the dominance or influence of people native in a particular place or
Ada
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Source:  OpenStax, Cell biology. OpenStax CNX. Jan 04, 2014 Download for free at https://legacy.cnx.org/content/col11570/1.3
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