microorganisms Flashcards
cell types:
prokaryotes- bacteria, archaea.
eukaryotes- all cells apart from bacteria and archaea.
the major bacterial groups:
bacteria are divided into 23 groups or phyla. the largest group is the proteobacteria. It is an extremely diverse group- most physiological types are represented and the wide range of morphological forms that they possess gives rise to the groups name. (proteus was a mythological Greek god who was able to assume many forms.)
all members of the group are gram negative.
the gram stain:
a differential stain, it does not stain all kinds of cells the same. Bacteria can be divided into 2 major groups, gram positive and gram negative. After staining, gram positive bacteria appear purple, and gram negative appear red. The difference in reaction is because of differences in the cell wall structure and composition of gram positive and gram negative cells.
the proteobacteria:
currently more than 460 genera and 1600 species have been identified, all of which are gram negative and representing almost half of all accepted bacterial genera. The group includes E coli.
importance of fungi:
Production of antibiotics (penicillin), cyclosporins (immunosuppressants in transplant surgery), modification of steroids (contraceptives)
Cell factories for the production of foreign gene products- yeast production of hepatitis B vaccine.
Decomposition of complex plant and animal remains in natural environments such as soil.
Rotting of food, textiles including timber, dry rot caused by serpula lacrymans.
These are all carried out by saprotrophic fungi. There are also parasitic (pathogenic) fungi, which cause diseases of plants and animals. And symbiotic fungi, which form lichens and mycorrhizas.
fungal pathogens of humans:
there are only 200 fungi that infect humans or other warm blooded animals. Humans have a high degree of innate immunity to fungi, with the exception of the dermatophytic fungi, which commonly cause infections of the skin, nails and hair. With the advance of AIDS and the increasing role of transplant surgery, fungi are becoming one of the most significant causes of death of immunocompromised and immunosuppressed patients. There are a few antifungal drugs available to treat the major fungal infections.
characteristics of fungi:
heterotrophic for carbon, eukaryotic cell structure, filamentous in most groups, cell wall present, spores produced in reproduction, non motile except in reproduction in some fungi.
filamentous:
each filament is called a hypha. network of branched hyphae is called the mycelium.
fairy rings show how fungi grow. ringworm is an example of the circular growth pattern.
cell wall is present:
the walls of all fungi contain a mixture of fibrillar and amorphous or matrix components.
The fibrillar components are normally composed of chitin B (1-4) linked polymer of N-acetyl-glucosamine and form a network which confers rigidity to the wall.
The amorphous components include proteins, mannans (polymer of mannose) and glucans (B(1-3), B(1-6) and A(1-3) linked polymers of glucose).
septation:
in the majority of fungi, the hyphae as they grow apically, become divided, at intervals, by transverse walls or septa into compartments.
2 large divisions within the fungi regularly septate- higher fungi aseptate- lower fungi.
spores produced in reproduction:
fungi produce spores for dispersal and survival. There are 2 major types of spores: sexual spores, which are thick walled and resistant to unfavourable environmental conditions and asexual spores, which are produced in very large numbers for dispersal but normally have low resistance to unfavourable conditions.
asexual reproduction- non motile sporangiospores.
sexual reproduction- zygospores.22
