Lecture 3 - Endoplasmic Reticulum | Cell Biology- Botany PDF Download

 Page 1


Endoplasmic Reticulum 
Institute of Lifelong Learning, University of Delhi 0 
 
 
 
 
 
 
 
 
Subject: Cell Biology 
Lesson: Endoplasmic Reticulum 
Lesson Developer: Manju A.Lal 
College/ Department: Botany Department, Kirori Mal College, University 
of Delhi 
  
  
Page 2


Endoplasmic Reticulum 
Institute of Lifelong Learning, University of Delhi 0 
 
 
 
 
 
 
 
 
Subject: Cell Biology 
Lesson: Endoplasmic Reticulum 
Lesson Developer: Manju A.Lal 
College/ Department: Botany Department, Kirori Mal College, University 
of Delhi 
  
  
Endoplasmic Reticulum 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents 
? Introduction 
? Overview of the endomembrane system 
? Discovery of ER 
? Experimental approaches which led to understanding about ER 
? Features of Endoplasmic reticulum 
? Types of ER 
? RER 
? SER 
? Role of RER: 
? Protein synthesis  
? Synthesis of secretory proteins  
? Synthesis of integral membrane proteins 
? Processing of proteins 
o Glycosylation of proteins 
o Folding of proteins 
o Quality control of proteins 
o Post-translational entry of proteins 
? Role of SER:  
? Drug detoxification 
? Lipid biosynthesis 
? Regulation of glucose level in blood 
? Storage of calcium 
 
 
 
 
 
 
 
Page 3


Endoplasmic Reticulum 
Institute of Lifelong Learning, University of Delhi 0 
 
 
 
 
 
 
 
 
Subject: Cell Biology 
Lesson: Endoplasmic Reticulum 
Lesson Developer: Manju A.Lal 
College/ Department: Botany Department, Kirori Mal College, University 
of Delhi 
  
  
Endoplasmic Reticulum 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents 
? Introduction 
? Overview of the endomembrane system 
? Discovery of ER 
? Experimental approaches which led to understanding about ER 
? Features of Endoplasmic reticulum 
? Types of ER 
? RER 
? SER 
? Role of RER: 
? Protein synthesis  
? Synthesis of secretory proteins  
? Synthesis of integral membrane proteins 
? Processing of proteins 
o Glycosylation of proteins 
o Folding of proteins 
o Quality control of proteins 
o Post-translational entry of proteins 
? Role of SER:  
? Drug detoxification 
? Lipid biosynthesis 
? Regulation of glucose level in blood 
? Storage of calcium 
 
 
 
 
 
 
 
Endoplasmic Reticulum 
Institute of Lifelong Learning, University of Delhi 2 
Introduction 
Proteins are synthesized by the ribosomes. The ribosomes are present either free in the 
cytoplasm or attached to cytoplasmic membranes. There are about 20,000 different types of 
proteins synthesized in a typical eukaryotic cell, which include various types of enzymes, different 
types of membrane proteins and secretary proteins. These proteins have to reach their respective 
destinations, so that various organelles can perform their functions. 
So, how do proteins reach their respective destinations? One of the way, by which proteins are 
sorted out and reach their destinations is through the network of endomembrane system. 
What is endomembrane system? 
There is a dynamic network of membranes, through which proteins and other molecules are 
transported and distributed within the cell and also targeted out of the cell. This is called 
endomembrane system. The endomembrane system is dynamic and is an integrated network of 
the membrane bound structures. 
The important components of endomembrane system are:- 
? Endoplasmic reticulum (ER) 
? Golgi apparatus 
? Lysosomes 
The composition of fluid and the membrane of each of them is unique. There is continuity in 
between these components through the vesicles. There is exchange of proteins and various other 
materials through these vesicles, besides movement of the membranes. So, it is important to 
study vesicular trafficking.  
In this chapter you will study about endoplasmic reticulum. The objectives of the chapter are to 
learn about: 
1. What are the components of endomembrane system? 
2. What is endoplasmic reticulum? 
3. How has this been discovered? 
4. Structure and types of ER. 
5. Role of ER.  
 
 
 
 
Page 4


Endoplasmic Reticulum 
Institute of Lifelong Learning, University of Delhi 0 
 
 
 
 
 
 
 
 
Subject: Cell Biology 
Lesson: Endoplasmic Reticulum 
Lesson Developer: Manju A.Lal 
College/ Department: Botany Department, Kirori Mal College, University 
of Delhi 
  
  
Endoplasmic Reticulum 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents 
? Introduction 
? Overview of the endomembrane system 
? Discovery of ER 
? Experimental approaches which led to understanding about ER 
? Features of Endoplasmic reticulum 
? Types of ER 
? RER 
? SER 
? Role of RER: 
? Protein synthesis  
? Synthesis of secretory proteins  
? Synthesis of integral membrane proteins 
? Processing of proteins 
o Glycosylation of proteins 
o Folding of proteins 
o Quality control of proteins 
o Post-translational entry of proteins 
? Role of SER:  
? Drug detoxification 
? Lipid biosynthesis 
? Regulation of glucose level in blood 
? Storage of calcium 
 
 
 
 
 
 
 
Endoplasmic Reticulum 
Institute of Lifelong Learning, University of Delhi 2 
Introduction 
Proteins are synthesized by the ribosomes. The ribosomes are present either free in the 
cytoplasm or attached to cytoplasmic membranes. There are about 20,000 different types of 
proteins synthesized in a typical eukaryotic cell, which include various types of enzymes, different 
types of membrane proteins and secretary proteins. These proteins have to reach their respective 
destinations, so that various organelles can perform their functions. 
So, how do proteins reach their respective destinations? One of the way, by which proteins are 
sorted out and reach their destinations is through the network of endomembrane system. 
What is endomembrane system? 
There is a dynamic network of membranes, through which proteins and other molecules are 
transported and distributed within the cell and also targeted out of the cell. This is called 
endomembrane system. The endomembrane system is dynamic and is an integrated network of 
the membrane bound structures. 
The important components of endomembrane system are:- 
? Endoplasmic reticulum (ER) 
? Golgi apparatus 
? Lysosomes 
The composition of fluid and the membrane of each of them is unique. There is continuity in 
between these components through the vesicles. There is exchange of proteins and various other 
materials through these vesicles, besides movement of the membranes. So, it is important to 
study vesicular trafficking.  
In this chapter you will study about endoplasmic reticulum. The objectives of the chapter are to 
learn about: 
1. What are the components of endomembrane system? 
2. What is endoplasmic reticulum? 
3. How has this been discovered? 
4. Structure and types of ER. 
5. Role of ER.  
 
 
 
 
Endoplasmic Reticulum 
Institute of Lifelong Learning, University of Delhi 3 
Overview of the endomembrane system 
 
Figure: Endomembrane system 
Source: ILLL In house 
As mentioned earlier three organelles constitute the endomembrane system and materials are 
transported/ shuttled inside the cell from one part to the other. Transport vesicles bud from one 
compartment and move to the other carrying materials. On reaching their destinations these 
vesicles fuse with the membrane of the of the acceptor compartment and release their cargo. This 
repeated cycles of budding and fusion carries materials across the cell. 
 
 
Page 5


Endoplasmic Reticulum 
Institute of Lifelong Learning, University of Delhi 0 
 
 
 
 
 
 
 
 
Subject: Cell Biology 
Lesson: Endoplasmic Reticulum 
Lesson Developer: Manju A.Lal 
College/ Department: Botany Department, Kirori Mal College, University 
of Delhi 
  
  
Endoplasmic Reticulum 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents 
? Introduction 
? Overview of the endomembrane system 
? Discovery of ER 
? Experimental approaches which led to understanding about ER 
? Features of Endoplasmic reticulum 
? Types of ER 
? RER 
? SER 
? Role of RER: 
? Protein synthesis  
? Synthesis of secretory proteins  
? Synthesis of integral membrane proteins 
? Processing of proteins 
o Glycosylation of proteins 
o Folding of proteins 
o Quality control of proteins 
o Post-translational entry of proteins 
? Role of SER:  
? Drug detoxification 
? Lipid biosynthesis 
? Regulation of glucose level in blood 
? Storage of calcium 
 
 
 
 
 
 
 
Endoplasmic Reticulum 
Institute of Lifelong Learning, University of Delhi 2 
Introduction 
Proteins are synthesized by the ribosomes. The ribosomes are present either free in the 
cytoplasm or attached to cytoplasmic membranes. There are about 20,000 different types of 
proteins synthesized in a typical eukaryotic cell, which include various types of enzymes, different 
types of membrane proteins and secretary proteins. These proteins have to reach their respective 
destinations, so that various organelles can perform their functions. 
So, how do proteins reach their respective destinations? One of the way, by which proteins are 
sorted out and reach their destinations is through the network of endomembrane system. 
What is endomembrane system? 
There is a dynamic network of membranes, through which proteins and other molecules are 
transported and distributed within the cell and also targeted out of the cell. This is called 
endomembrane system. The endomembrane system is dynamic and is an integrated network of 
the membrane bound structures. 
The important components of endomembrane system are:- 
? Endoplasmic reticulum (ER) 
? Golgi apparatus 
? Lysosomes 
The composition of fluid and the membrane of each of them is unique. There is continuity in 
between these components through the vesicles. There is exchange of proteins and various other 
materials through these vesicles, besides movement of the membranes. So, it is important to 
study vesicular trafficking.  
In this chapter you will study about endoplasmic reticulum. The objectives of the chapter are to 
learn about: 
1. What are the components of endomembrane system? 
2. What is endoplasmic reticulum? 
3. How has this been discovered? 
4. Structure and types of ER. 
5. Role of ER.  
 
 
 
 
Endoplasmic Reticulum 
Institute of Lifelong Learning, University of Delhi 3 
Overview of the endomembrane system 
 
Figure: Endomembrane system 
Source: ILLL In house 
As mentioned earlier three organelles constitute the endomembrane system and materials are 
transported/ shuttled inside the cell from one part to the other. Transport vesicles bud from one 
compartment and move to the other carrying materials. On reaching their destinations these 
vesicles fuse with the membrane of the of the acceptor compartment and release their cargo. This 
repeated cycles of budding and fusion carries materials across the cell. 
 
 
Endoplasmic Reticulum 
Institute of Lifelong Learning, University of Delhi 4 
 
Figure: Movement of material carried by the transport vesicles from the donor to the recipient 
compartments 
Source: ILLL In house 
 
 The materials are transported along several pathways:  
? Biosynthetic or secretory pathway- Proteins synthesized in ER are transported and 
modified in the Golgi complex and then secreted to various destinations like plasma 
membrane, lysosomes etc. The secretory pathway can be constitutive (continual 
secretion of material destined for the plasma membrane and extracellular matrix) or 
regulated with gradual release in response to specific signals. For e.g. the release of 
hormones in endocrine cells. 
? Endocytic pathway- This pathway operates in opposite direction to the biosynthetic 
pathway, with materials moving from outside of the cell to the organelles inside the cell  
like lysosome etc.