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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

If Jane was in room(B) while her mother Stella was in room (Y). Jane was cooking fish, her mother came to smell the good scent, By what process did her mother came to smell the scent
Neimar Reply
Is it a serious question?
Ehsan Reply
what's the question
how many days do a bean seed take to germinate
what is DNA
Yahaya Reply
genetic information
Deoxyribonucliec acid (DNA) is the cell's hereditary material that contains instructions for growth, development and reproduction.
what's different between sex and gender
Are there differences between sex and gender?
describe an experiment to show that plants require light for photosynthesis
Diyara Reply
What's an amoeba
Bigger Reply
An amoeba is a cell or an organism that has the ability to ulter it's shape.
An amoeba has an irregular shape and it changes constantly,it's a unicellular organism belong to a group called protists it has a pseudopodia used for locomotion and ingestion...
what is a zygote?
Darius Reply
zygote is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information necessary to form a new individual.
A zygote is an organism formed after fertilization
how do plants form a zygote
Paclina Reply
What is zygote
what is zygote
Zygote is located inside the ovule, which is present in the ovary.
zygote is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information necessary to form a new individual.
what is biology?
Aadan Reply
biology is the study of living n non living organism
what is procotist?
Biology is the branch of science that deals with the study of living and non living things
Describe at least two major changes to the animal phylogenetic tree that have come about due to molecular or genetic findings.
Tamala Reply
what is herbarium sheet
Ramreichon Reply
Which of the following is not a characteristics of all living organisms? A. Excretion B. Photosynthesis C. Reproduction D. Respiration
B photosynthesis
general equation for photosynthesis
Ojasope Reply
6CO2 + 6H2O + solar energy= C6H1206+ 6O2
meaning of amino Acids
An aminoacid is a base unit molecule for proteins. It s formed by a central Carbon, to which are attached: an amminic Group, a carbossilic Group, an H hydrogen, and an R group ( which varies for each different aminoacid). Glycin is the only aminoacid to have for an R group a simple H hydrogen.
H NH2-C-COOH R this is the not ionized form but usually they are ionized, with NH+ and COO-
The R group, the lateral Chain, is responsible for the characteristics of the aminoacid.
* NH2+
J=1 jar daq
a diagram of an adult mosquito
mubarak Reply
what are white blood cells
Mlungisi Reply
white blood cell is part of the immune system. that help fight the infection.
what about tissue celss
Cells with a similar function, form a tissue. For example the nervous tissue is composed by cells:neurons and glia cells. Muscle tissue, is composed by different cells.
white blood cells are components of blood that help the body fight diseases
I need further explanation coz celewi anything guys,,,
Calvin Reply
hey guys
on what?
Please define mitosis for me
mitosis is a process where a single cell divides into two identical daughter cells(cell division)
What about meiosis
Meiosis is a process that produces gametes. From a single cell, 4 daughter cells (gametes) are formed.
What is a tissue respiration

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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