Structure and propagation of fungi, protozoa,
and bacteriophages
FUNGI
• Fungal cells are organized a little differently from
animal and plant cells. Like plant cells, they have a cell
wall; however, unlike plant cells, the cell wall lacks
cellulose (in true fungi) and there are no chloroplasts.
• The typical fungal structure is that of a colony of cells
strung together in a filament called a Hypha (plural,
hyphae). The cells in a hypha are separated by a crosswall called a Septum. Hyphae tend to form a larger
network of cells called a Mycelium. Fungal hyphae
have a number of unique features:
Cell Wall:
The cell wall has four main biochemical constituents:
• a) Chitin – microfibrils – Chitin is a polymer of the sugar N-acetyl
glucosamine formed by chitin synthase. (Oomycetes have cellulose, a
glucose polymer, instead). The microfibrils form a high strength mesh in
the cell wall.
• b) Glucans – These are polymers of glucose bound in a variety of
covalent bonds. Unlike chitin they aren’t in any set pattern, and as such
are said to be amorphous.
• c)
Proteins – A variety of proteins are included in the structure. Waterresistant hydrophobins make up a dehydration resistant layer when the
hypha is in contact with the air. Over 6% of all proteins in the cell are in
the hydrophobin class.
• d) Melanin – This black pigment helps prevent ultraviolet radiation
damage, and acts to make the cell wall even tougher. Melanins are formed
by the action of phenoloxidase enzymes (laccase, tyrosinase and
peroxidase, for example) on phenolic compounds.
Septum (plural, septa): This structure can be thought of as a valve
between adjacent hyphal cells to prevent the accidental loss of cell
organelles between hyphal compartments. Pores within the septa
allow the organelles and nutrients to flow freely when required. Not
all fungi have septa. Oomycetes lack septa, and the form of septum
varies from phylum to phylum. Ascomycetes have simple septa.
Basidiomycetes have a more complex system for preventing the loss
of material between adjacent cells. The Dolipore septa are
restrictive to the extent that the migration of nuclei is only possible
under certain circumstances (mating), when the septum dissolves.
Propagation of fungi
• Asexual
1. Bud formation
2. Fragmentation
3. Sporulation
• Sexual reproduction
I. Chytridiomycetes
II. Zygomycetes
III. Ascomycetes
IV. Basidiomycetes
Protozoa
Protozoans
• What are the
characteristics of
protozoans?
9.1 Protozoans
• A protozoan is a singlecelled eukaryotic animal.
• Protozoans are most
often placed in the
Kingdom Protista with
algae and slime molds.
Protozoans need a moist
environment to survive.
ASEXUAL REPRODUCTION
BINARY FISSION
• TYPES OF BINARY FISSION
1. The binary fission is irregular in - Amoeba proteus
2. Longitudinal in - Euglena
3. Transverse in – Paramecium
MULTIPLE FISSION
• The division of the parent into numerous daughter individuals is called - multiple
fission (e.g. sarcodines and sporozoans)
PLASMOTOMY
• The division of a multinucleate protozan into multinucleate duaghter individuals by
cytoplasmic division but without nuclear divisional is called - Plasmotomy eg :
Opalina
BUDDING
• Budding is common in - Suctorian protozoans eg : Acinata
Sexual reproduction
• Conjugation
Temporary pairing or two individuals for the exchange of the pronuclei and the fusion
of pronuclei takes place during e.g. paramecium
bacteriophages
• A bacteriophage is a virus that infects and replicates
within a bacterium.
• Bacteriophages
are
composed
of proteins that encapsulate a DNA or RNA genome,
and may have relatively simple or elaborate
structures. Their genomes may encode as few as
four genes, and as many as hundreds of genes. Phages
replicate within the bacterium following the injection
of their genome into its cytoplasm. Bacteriophages
are among the most common and diverse entities in
the biosphere.