3. Cell wall was first observed and named
simply as a “wall” by Robert Hooke in
1665.
In 1804, Karl Rudolphi and J.H.F. Link
proved that cells have independent cell
walls.
A cell wall is a structural layer that
surrounds types of cells, situated outside
the cell membrane.
It can be tough, flexible and rigid which
provides cell with both structural support
and protection.
4. On the basis of chemical composition of
cell wall there are three types of cell
wall:
1) Bacterial Cell Wall: made up of
Mucopeptide and Muramic acid.
2) Cell wall of Fungi: made up of
Chitin.
3) Plant Cell wall: made up of
Cellulose.
5. Major component is Peptidoglycan(strong
shell).
Gram negative bacteria: thin
peptidoglycan layer(thin cell wall).
Gram positive bacteria: thick
peptidoglycan layer(thick cell wall).
Archeal cell wall lacks peptidoglycan.
It is composed of pseudopeptidoglycan,
sulfated polysaccharides,
glycoprotiens.
6. Multi layered and more complex than
gram positive cell walls.
Peptidoglycan of gram negative bacteria
is thin comprises only 10% or less of
cell wall.
Outer membrane lies outside the thin
peptidoglycan layer.
Most abundant protein is Braun’s
lipoprotein.
7. Usually thick, homogenous, composed
mainly of peptidoglycan.
It accounts 50- 90% of the dry weight
of the cell wall.
Contain large amount of teichoic acids.
8.
9. Developed by Christian Gram in 1884.
https://www.youtube.com/watch?v=sxa46xKfIOY
10. Click on this video link below for a better
understanding of the procedure of gram staining
technique.
https://youtu.be/sxa46xKfIOY
11. Peptidoglycan ,also known as murein, is a
polymer consisting of sugars and amino acids
that forms a mesh-like layer outside the cell
membrane of most bacteria forming cell wall.
The sugars component consist of alternating
residues of β-(1,4) linked N- acetyl
glucosamine and N-acetylmuramic acid.
These subunits which are related to glucose in
their structure are covalently joined to one
another to form glycan chains.
Attached to the N- acetylmuramic acid is a
peptide chain of three to five amino acids.
The peptide chain can be cross- linked to the
peptide chain of another strand forming the
peptidoglycan.
12.
13. Composed of Chitin(polysaccharide)in fungi
and Cellulose(polymer)in plants.
Both cellulose and chitin shows β-1,4
linkage.
14. The cell wall is made up of :
1.Chitin (polymers of acetylated amino
sugar N-acetylglucosamine)
2.Glucans
3.Proteins
Glucan and Chitin are components of the
primary wall.
Proteins are components of the
secondary wall.
Other components include chitosan,
melanins and lipids
17. Middle lamella– first formed from cell
plate during cytokinesis.
Primary cell wall- composed of cellulose
fibrils, produced at plasma membrane by
cellulose synthase complex.
Microfibrils– held by hydrogen
bonds(tensile strength).
Secondary cell wall– constructed between
plasma membrane and primary wall.
Plasmodesmata– interconnecting channels of
cytoplasm that connect protoplasts.
18. 1. Middle Lamella
It is present between two adjacent
cells.
It is situated outside primary cell
wall and is made up of calcium and
magnesium pectate.
It acts as cement which holds the
adjacent cells together.
19. 2. Primary Cell Wall
It is formed after the middle lamella.
A thin, flexible and extensible layer.
It is capable of growth and expansion.
The backbone of primary cell wall is
formed by the cellulose fibrils.
The matrix is composed of hemicellulose,
pectin compounds, lipids, structural
proteins.
Hemicelluloses are highly branched
polysaccharides that are H-bonded to
cellulose microfibrils into a tough fiber,
which is responsible for the mechanical
strength of plant cell wall.
20. • The cellulose microfibrils and
hemicelluloses are embedded in a gel-like
matrix formed by pectins, which are
branched polysaccharides containing a large
number of negatively-charged galacturonic
acid residues. Because of these multiple
negative charges, pectins bind positively-
charged ions(such as Ca2+)and trap water
molecules to form gels.
21.
22. 3. Secondary Cell Wall
It is extremely rigid and provides
strength.
It is not found in all cell types.
It consists of three layers known as
S1(outer),S2(middle) and S3(inner).
It is composed of cellulose,
hemicellulose and lignin.
Lignin is a complex polymer of
hydrophobic phenolic residues, which
inserts into the spaces between the
other polymers. Lignin is responsible
for much of the strength and density of
wood.
23.
24. 4. Tertiary Cell Wall
Tertiary cell wall is deposited in few
cells.
It is considered to be dry residue of
protoplast .
Besides cellulose and hemi-cellulose,
xylan is also present.
Plasmodesmata
Plasmodesmata are protoplasmic strands
that connect the protoplasts of
neighboring cells.
Diameter is 40-50 nm.
27. Many animal cells are intrinsically linked
to other cells and to the extracellular
matrix (ECM).
Cell surface molecules bind to other
cells, or to other components of the ECM.
They also play a role in mutual
recognition of similar cell types.
Bone and cartilage are mostly ECM plus a
very few cells. Connective tissue that
surrounds glands and blood vessels, is a
gelatinous matrix containing many
fibroblast cells.
28. The ECM contains 3 classes of molecules:
Structural proteins (collagens and
elastins)
Protein-polysaccharide complexes to embed
the structural proteins (proteoglycans)
Adhesive glycoproteins to attach cells to
matrix (fibronectins and laminins).
29.
30. Most abundant protein in animals-25%
Secreted mostly by connective tissue cell
and in small quantity by other cell
Collagen contributes to the stability of
tissues and organs.
It maintains their structural integrity.
It has great tensile strength.
The main component of fascia, cartilage,
ligaments, tendons, bone and skin.
Plays an important role in cell
differentiation, polarity, movement.
Plays an important role in tissue and
organ development.
31. Human genome contains 42 distinct a-chain
genes (42 can undergo different combinations
Less than 40 types of collagen found so far
Triple helix of 3 α-chains
α-chain structure Gly-X-Y repeats in a left
handed turn
X frequently a proline
Y frequently a hydroxylysine or hydroxyproline
(mostly)
Proline and hydroxyproline makes the chain
more rigid
The glycine because of its small nature is
able to be accommodated in the crowded helix
36. Several other types of
collagen do not form fibrils
but play distinct roles in
various kinds of
extracellular matrices.
Type-IV collagen do not form
fibrils but form a mesh-like
network.
Basal lamina form from
different types of collagen,
primarily type-IV collagen,
but also type VI and XVIII,
all of which are network-
forming collagens.
37. Elastin is a major protein component of
tissues that require elasticity such as
arteries, lungs, bladder, skin and elastic
ligaments and cartilage.
It is composed of soluble tropoelastin protein
containing primarily glycine and valine and
modified alanine and proline residues.
It is secreted by connective tissue cells as
soluble tropoelastin into EC matrix.
Forms cross linkages with each other-catalysed
by lysil oxidase
Forms an extensive network of elastin fibres
and sheets
Elastin fibres associate with microfibrils
made up of glycoproteins including fibrillin
38. Polypeptide chains are cross-linked together
to form rubberlike, elastic fibers. Each
elastin molecule uncoils into a more extended
conformation when the fiber is stretched and
will recoil spontaneously as soon as the
stretching force is relaxed
39. Many different genetic
types
Triple helix
(Gly-X-Y)n repeating
structure
Presence of
hydroxylysine
Carbohydrate-containing
Intramolecular aldol
cross-links
Presence of extension
peptides during bio-
synthesis
One genetic type
No triple helix;
random coil
conformations
permitting stretching
No (Gly-X-Y)n
repeating structure
No hydroxylysine, No
carbohydrate
Intramolecular
desmosine cross-links
No extension peptides
present during
biosynthesis
Collagen Elastin
40. Unbranched polysaccharide chains composed
of repeating dissacharide units.
Negatively charged under physiological
conditions (due to the occurrence of
sulfate and uronic acid groups)
Disaccharide subunits are:
1. Uronic acid
D-glucuronic acid or L-iduronic acid
2. Aminosugar
N-acetylglucosamin (GlcNAc) or
N-acetylgalactosamin (GalNAc)
41. Amino sugars and uronic acids are the most
common building blocks of the
glycosaminoglycans.
Amino sugars : -OH at C-2 is replaced by
an amino group. This amino group is most
often acetylated and sometimes sulfated.
Uronic acids : C-6 of the hexose is
oxidized to a carboxyl group.
Common sulfated GAGs are dermatan sulfate,
chondroitin sulfate, keratin sulfate, and
haparan sulfate.
(Exception: Hyaluronan is a non-sulfated GAG
and the only GAG that occurs as a single long
polysaccharide chain)
42.
43. Proteins linked covalently to
glycosaminoglycans (GAGs).
Carbohydrates(polysaccharides) make up
about 95% of its weight.
Proteins bound covalently to GAGs are
called core proteins.
Many have been classified; they vary in
tissue of origin, function, core
protein types.
Examples include aggrecans, syndecan,
betaglycan, serglycan.
44.
45. A number of
proteoglycans interact
with hyaluronan to
form large complexes
in the ECM. A well-
characterized example
is aggrecan, the major
proteoglycan of
cartilage.
46. Principal adhesion protein of connective
tissues.
Dimeric glycoprotein consisting of two
polypeptide chains , each containing nearly
2500 amino acids.
Has binding sites for both collagen and
GAGs so it cross-links these matrix
components.
Attached to cell membrane by membrane-
spanning receptor – integrin.
Derived by alternative splicing of the mRNA
of a single gene.
47. Laminins are cross- or T-shaped
heterotrimers of α,β,and γ subunits, which
are the products of five α genes, three β
genes, and three γ genes.
Principal components of basal laminae.
Like type-IV collagen, laminins can self-
assemble into meshlike networks.
Laminins are tightly associated with another
adhesion protein, called nidogen, which also
binds to type-IV collagen.
Laminin, nidogen, collagen, and the
proteoglycans form cross-linked networks
within basal laminae.
