Download INTRODUCTION TO MYCOLOGY

MYCOLOGY
(MIC 206)
FUNGAL CELL
FUNGAL CELL
The composition of the
fungal cell wall is rather
variable.
The variability → to have
phylogenetic significance
A cell wall surrounds fungal cells (not present in human cells)
and their slightly different metoblism provides targets for
antifungal compounds.
Characteristics of Fungal Cell
Gives shape to fungi.
Gives strength to fungi.
Provides protection for the protoplasm from ultraviolet rays (presence of melanins)
Ability to resist lysis by organic solvents such as
enzymes, toxins, osmotic integrity.
Ability to bind with metal ions.
Secretes enzymes from their walls (invertase
hydrolyses sucrose to glucose and fructose) and so
assisting in nutrition.
The
main
identifying
characteristic of fungi is the
makeup of their cell walls.
Many contain a nitrogenous
substance known as "chitin,"
which is not found in the cell
walls of plants, but can be
found in the outer shells of
some crabs and mollusks.
Fungal cell wall is (metabolic
point of view) very different
from insect exoskeletons or a
plant cell walls, → terminally
differentiated structures.
Cell Wall
The cell wall is made up of:
1) chitin (polymers of acetylated amino sugar
N-acetyl-glucosamine)
2) glucan (polymers of glucose)
3) proteins (polymers of amino acids).
Glucan and chitin are components of the
primary wall.
Proteins are components of the secondary wall.
Basic component of fungal cell wall
Fungal Cell
Other components include chitosan, melanins
and lipids.
Enzymes include cellulase which acts on
cellulose of plants.
The outermost surface of the cell wall
1) provides a medium between the cell and the
environment
2) a site where antigen and agglutinin gets
attached to the substrate, host and other
cells.
Chitin
Chained polymer β(1-4) N-acetyl-glucosamine.
Found naturally as structural polysacharides in
most invertebrates and protistans. They are used
as cell wall components.
Gives strength where each molecule contains a
unit of sugar that is bonded by hydrogen bond to
give it rigidity.
Each microfibril of chitin gives the shape of the cell
and gives strength to mature cell walls.
Microfibrils can be of various shapes:


in yeast: short and thick
in hyphal wall: long and interwoven
Chitin (cont)
Septa is rich in chitin
Microfibrils of septa are arranged in the form
of a tangent.
Septa can be stained with “calcoflour
white”.
Saccharomyces cerevisiae has low amount
of chitin.
Chitosan
Chained β(1-4) glucosamine.
Result of continuous acetylation of chitin.
An important component in wall of
Zygomycetes and can be found in
ascospore walls of Saccharomyces
cerevisiae.
Glucan
Most fungal walls contain βchained glucan.
Walls of Ascomycetes and
Basidiomycetes contain β(13) glucan with branching of
β(1-6) glucan.
In Schizophyllum commune,
the hypha is protected by
mucilage made up of β(1-6)
glucan and therefore can
make colonies of gelatins.
There are some fungi with
α(1-4) glucan.
The shiitake mushroom
contains beta-glucans.
β-Glucans are polysaccharides of D-glucose
monomers linked by β-glycosidic bonds.
Diagram showing orientation and location
of different beta-glucan linkages.
Glycoprotein and Protein
Glycoproteins (include mannoprotein,
galactoprotein and xyloprotein) are important
components of the matrics of cell walls.
Protein contain chains of manocil-6phosphoryll.
Glycoprotein contain glucosamine and/or Nacetyl glucosamine.
In parasitic fungi such as Candida albicans and
Aspergillus fumigatus, the glycoproteins are
antigens.
Mannoprotein in Saccharomyces cerevisiae
are large molecules.
Glycoprotein and Protein
(cont)
Hydrophobin is a very hydrophobic protein
and found in aerial hyphae of Schizophyllum
commune and are components of rodlets.
Rodlets are found on the surface of conidia of
Neurospora crassa and Aspergillus nidulans
and protects the hyphae from desiccation.