Lecture 1 - Cell Wall | Cell Biology- Botany PDF Download

 Page 1


Cell wall 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
 
 
 
Subject: Cell Biology 
Lesson: Cell Wall 
Lesson Developer: Rina Majumdar 
College/ Department: Maitreyi college, University of Delhi 
Page 2


Cell wall 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
 
 
 
Subject: Cell Biology 
Lesson: Cell Wall 
Lesson Developer: Rina Majumdar 
College/ Department: Maitreyi college, University of Delhi 
Cell wall 
 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents       
 
Chapter: Cell wall 
? Introduction  
? Importance 
? Chemistry of the cell wall 
? Bacterial cell wall 
? Gram positive and negative bacteria 
? Cell wall in archea 
? Eukaryotic cell wall 
o Wall layers 
? Middle lamella 
? Primary cell wall 
? Secondary cell wall 
o Composition of the cell wall 
? Cellulose 
? Hemicellulose 
? Pectin 
? Glycoprotein 
? Lignin 
? Cutin, suberin and waxes 
? Algal cell wall 
? Fungal cell wall 
? Formation of cell wall 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
Page 3


Cell wall 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
 
 
 
Subject: Cell Biology 
Lesson: Cell Wall 
Lesson Developer: Rina Majumdar 
College/ Department: Maitreyi college, University of Delhi 
Cell wall 
 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents       
 
Chapter: Cell wall 
? Introduction  
? Importance 
? Chemistry of the cell wall 
? Bacterial cell wall 
? Gram positive and negative bacteria 
? Cell wall in archea 
? Eukaryotic cell wall 
o Wall layers 
? Middle lamella 
? Primary cell wall 
? Secondary cell wall 
o Composition of the cell wall 
? Cellulose 
? Hemicellulose 
? Pectin 
? Glycoprotein 
? Lignin 
? Cutin, suberin and waxes 
? Algal cell wall 
? Fungal cell wall 
? Formation of cell wall 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
Cell wall 
 
Institute of Lifelong Learning, University of Delhi 2 
 
Introduction 
Cell wall is one of the unique features in the plant cell that distinguishes it from the animal 
cell.  The boundary of each cell in plants is, defined by the cell wall.  It is made of insoluble 
structural polysaccharide secreted by the cells.  The plasma membrane forms the outermost 
layer in animal cells where as in plants the plasma membrane lies next to the cell wall, 
which provides an elaborate extracellular matrix. Plant cell wall can be modified in response 
to changing environmental conditions. 
Importance 
Cell wall represents the outer covering of a cell, present outside the cell membrane. Cell 
wall is present in plants, algae, fungi and bacteria and is absent in animals and protozoans. 
It has key role in strengthening, plant growth, cell differentiation, water movement and 
defense. 
In plants, cell wall not only provides rigidity and strength but also forms a protective home 
for the cellular constituents. The definite shape of each plant cell is due to the presence of 
cell wall. The intact multicellular plant body is formed due to the cementing together of cell 
wall to that of its neighbors. In addition, direct cell-cell communication is possible through 
plasmodesmata, which are plasma membrane lined channels of cytoplasm that cross the 
cell wall. Besides protective function, cell wall also plays important role in cellular 
absorption, secretion, and transport across the cells, and various other functions.  Being, 
the outermost layer in plant cells , it also plays an important role in cellular defense against 
various pathogens.  Unlike animal cells, plant cells are, prevented from swelling and 
bursting because of osmotic pressure by the presence of cell wall outside. Cell wall also 
serves to store carbohydrates that can be broken down by enzymes and used by the cell. 
For e.g. the cell walls in endosperm of cereals are rich in glucans and polysaccharides and 
nourish the growing embryo during seed germination.  
To summarize some of the important functions of cell wall are:  
? Gives structural and mechanical support thus determining the overall form and 
architecture of the plant 
? Gives definite shape to the cell 
? Prevents cell from bursting by resisting the turgor pressure from inside the cell. 
? Regulates exchange of material through the apopalst 
? Determines the growth direction and rate 
? Protection 
Page 4


Cell wall 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
 
 
 
Subject: Cell Biology 
Lesson: Cell Wall 
Lesson Developer: Rina Majumdar 
College/ Department: Maitreyi college, University of Delhi 
Cell wall 
 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents       
 
Chapter: Cell wall 
? Introduction  
? Importance 
? Chemistry of the cell wall 
? Bacterial cell wall 
? Gram positive and negative bacteria 
? Cell wall in archea 
? Eukaryotic cell wall 
o Wall layers 
? Middle lamella 
? Primary cell wall 
? Secondary cell wall 
o Composition of the cell wall 
? Cellulose 
? Hemicellulose 
? Pectin 
? Glycoprotein 
? Lignin 
? Cutin, suberin and waxes 
? Algal cell wall 
? Fungal cell wall 
? Formation of cell wall 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
Cell wall 
 
Institute of Lifelong Learning, University of Delhi 2 
 
Introduction 
Cell wall is one of the unique features in the plant cell that distinguishes it from the animal 
cell.  The boundary of each cell in plants is, defined by the cell wall.  It is made of insoluble 
structural polysaccharide secreted by the cells.  The plasma membrane forms the outermost 
layer in animal cells where as in plants the plasma membrane lies next to the cell wall, 
which provides an elaborate extracellular matrix. Plant cell wall can be modified in response 
to changing environmental conditions. 
Importance 
Cell wall represents the outer covering of a cell, present outside the cell membrane. Cell 
wall is present in plants, algae, fungi and bacteria and is absent in animals and protozoans. 
It has key role in strengthening, plant growth, cell differentiation, water movement and 
defense. 
In plants, cell wall not only provides rigidity and strength but also forms a protective home 
for the cellular constituents. The definite shape of each plant cell is due to the presence of 
cell wall. The intact multicellular plant body is formed due to the cementing together of cell 
wall to that of its neighbors. In addition, direct cell-cell communication is possible through 
plasmodesmata, which are plasma membrane lined channels of cytoplasm that cross the 
cell wall. Besides protective function, cell wall also plays important role in cellular 
absorption, secretion, and transport across the cells, and various other functions.  Being, 
the outermost layer in plant cells , it also plays an important role in cellular defense against 
various pathogens.  Unlike animal cells, plant cells are, prevented from swelling and 
bursting because of osmotic pressure by the presence of cell wall outside. Cell wall also 
serves to store carbohydrates that can be broken down by enzymes and used by the cell. 
For e.g. the cell walls in endosperm of cereals are rich in glucans and polysaccharides and 
nourish the growing embryo during seed germination.  
To summarize some of the important functions of cell wall are:  
? Gives structural and mechanical support thus determining the overall form and 
architecture of the plant 
? Gives definite shape to the cell 
? Prevents cell from bursting by resisting the turgor pressure from inside the cell. 
? Regulates exchange of material through the apopalst 
? Determines the growth direction and rate 
? Protection 
Cell wall 
 
Institute of Lifelong Learning, University of Delhi 3 
? Cell – cell interaction 
? Storage in the form of wall carbohydrates 
? Source of biological signaling molecules 
 
 
Figure: Electron micrographs showing plasmodesmata (arrow) between two adjacent cells 
Source: http://pix.botany.org/set14/14-003h_300.jpg 
 
                                                                           
Figure: Diagrammatic representation of Plasmodesmata connecting the two cells via the 
apoplastic and symplastic pathways. 
Source: http://upload.wikimedia.org/wikibooks/en/0/00/Waterpathwaysthroughrootcells.gif 
 
Chemistry of the cell wall  
Chemical composition of the cell wall varies within different biological organisms. 
Bacterial cell wall 
Page 5


Cell wall 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
 
 
 
Subject: Cell Biology 
Lesson: Cell Wall 
Lesson Developer: Rina Majumdar 
College/ Department: Maitreyi college, University of Delhi 
Cell wall 
 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents       
 
Chapter: Cell wall 
? Introduction  
? Importance 
? Chemistry of the cell wall 
? Bacterial cell wall 
? Gram positive and negative bacteria 
? Cell wall in archea 
? Eukaryotic cell wall 
o Wall layers 
? Middle lamella 
? Primary cell wall 
? Secondary cell wall 
o Composition of the cell wall 
? Cellulose 
? Hemicellulose 
? Pectin 
? Glycoprotein 
? Lignin 
? Cutin, suberin and waxes 
? Algal cell wall 
? Fungal cell wall 
? Formation of cell wall 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
Cell wall 
 
Institute of Lifelong Learning, University of Delhi 2 
 
Introduction 
Cell wall is one of the unique features in the plant cell that distinguishes it from the animal 
cell.  The boundary of each cell in plants is, defined by the cell wall.  It is made of insoluble 
structural polysaccharide secreted by the cells.  The plasma membrane forms the outermost 
layer in animal cells where as in plants the plasma membrane lies next to the cell wall, 
which provides an elaborate extracellular matrix. Plant cell wall can be modified in response 
to changing environmental conditions. 
Importance 
Cell wall represents the outer covering of a cell, present outside the cell membrane. Cell 
wall is present in plants, algae, fungi and bacteria and is absent in animals and protozoans. 
It has key role in strengthening, plant growth, cell differentiation, water movement and 
defense. 
In plants, cell wall not only provides rigidity and strength but also forms a protective home 
for the cellular constituents. The definite shape of each plant cell is due to the presence of 
cell wall. The intact multicellular plant body is formed due to the cementing together of cell 
wall to that of its neighbors. In addition, direct cell-cell communication is possible through 
plasmodesmata, which are plasma membrane lined channels of cytoplasm that cross the 
cell wall. Besides protective function, cell wall also plays important role in cellular 
absorption, secretion, and transport across the cells, and various other functions.  Being, 
the outermost layer in plant cells , it also plays an important role in cellular defense against 
various pathogens.  Unlike animal cells, plant cells are, prevented from swelling and 
bursting because of osmotic pressure by the presence of cell wall outside. Cell wall also 
serves to store carbohydrates that can be broken down by enzymes and used by the cell. 
For e.g. the cell walls in endosperm of cereals are rich in glucans and polysaccharides and 
nourish the growing embryo during seed germination.  
To summarize some of the important functions of cell wall are:  
? Gives structural and mechanical support thus determining the overall form and 
architecture of the plant 
? Gives definite shape to the cell 
? Prevents cell from bursting by resisting the turgor pressure from inside the cell. 
? Regulates exchange of material through the apopalst 
? Determines the growth direction and rate 
? Protection 
Cell wall 
 
Institute of Lifelong Learning, University of Delhi 3 
? Cell – cell interaction 
? Storage in the form of wall carbohydrates 
? Source of biological signaling molecules 
 
 
Figure: Electron micrographs showing plasmodesmata (arrow) between two adjacent cells 
Source: http://pix.botany.org/set14/14-003h_300.jpg 
 
                                                                           
Figure: Diagrammatic representation of Plasmodesmata connecting the two cells via the 
apoplastic and symplastic pathways. 
Source: http://upload.wikimedia.org/wikibooks/en/0/00/Waterpathwaysthroughrootcells.gif 
 
Chemistry of the cell wall  
Chemical composition of the cell wall varies within different biological organisms. 
Bacterial cell wall 
Cell wall 
 
Institute of Lifelong Learning, University of Delhi 4 
The unicellular prokaryotic bacterial cells are characterized by the presence of cell wall 
made up of a unique polymer, found nowhere in other living organisms, known as 
Peptidoglycan/ Murein.  It is a hetero-polysaccharide consisting of alternating monomers 
of N-acetyl glucosamine (NAG) and N-acetyl muramic Acid (NAM) and joined by ß 
1 ?4 glycosidic linkage, arranged in parallel chains.   
 
Figure: N-acetyl glucosamine (NAG) and N-acetyl muramic Acid (NAM)  
Source: http://www.flickr.com/photos/ajc1/2281351707/ 
 
These parallel chains are, cross-linked by tetra-peptide attached to the NAM residues.  The 
amino acids forming the tetra-peptides vary in different species of bacteria. 
 
 
Figure:  The chains of N-acetyl glucosamine and N-acetyl muramic acid are joined together 
by peptide bridges in peptidoglycan 
Source: http://upload.wikimedia.org/wikipedia/commons/thumb/2/29/Mureine.svg/271px-
Mureine.svg.png  
Also visit: http://classes.midlandstech.edu/carterp/Courses/bio225/chap04/04-
13a_BactCellWall_1.jpg 
Gram positive and Gram negative bacteria