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.