Priscilla Johanesen; Week 2 MED1011; Microbiology
Three major domains are determined by RNA, bacteria and archaea are prokaryotes, eukarya are prokaryotes. Both prokaryotes and eukaryotes are surrounded by a plasma membrane, structurally very different (prokaryotes smaller and have a greater surface air to volume ratio). Prokaryotes are almost all unicellular, lack nuclei and organelles, contain genetic and protein synthesising systems, are different shapes (cocci, bacilli, spiral).
Prokaryotes have cytoplasm, ribosomes, nucleoid, plasma membrane and a cell wall containing peptidoglycan on the inside, outer membrane and a capsule. Peptidoglycan is unique to bacteria, is a complex carbohydrate and forms a strong mesh surrounding the cell. Gram staining involves crystal violet, water rinse, Gram's iodine, water rinse, ethanol/acetone, water rinse, safranin.
Gram positive cells have a thick cell wall with peptidoglycans, gram negative cells have a thin peptidoglycan layer which will be lost and stain will be washed out. Cell wall is a common target for combating disease as it is not found in eukaryotes, some antibiotics interfere with peptidoglycan synthesis. Flagella for motility has a long filament, can have single or multiple, on one end, both ends or all over, a single fibril is made of flagellin and rotates like a propeller.
- Vibrio cholerae has one flagellum, bacillus cereus and bacillus brevis have many
Pili and fimbriae project from cell surface, shorter than flagella, threadlike, aid in adherence of bacteria.
Bacteria replicate with binary fission. Prokaryotic environments are ubiquitous, oxygen requirements vary for strict aerobes, microaerophilic (need small amount of oxygen), facultative anaerobes (can be aerobic or anaerobic), aerotolerant anaerobe (can survive in oxygenated environment), strict anaerobes, other eg. carbon dioxide.
Eukaryotes have nucleus, ribosomes, mitochondrion, Golgi apparatus, smooth and rough endoplasmic reticulum, cell wall, lysosome, vacuoles, chloroplasts
|single cell||single or multicellular|
|simple structure||complex structure|
|no true nucleus||true nucleus|
|no membrane bound subcellular organelles||membrane bound subcellular organelles|
|complex cell wall||simple cell wall (plants) or membrane|
|divide by asexual binary fission||divide by asexual or sexual means|
|small cell size (0.4-2um diameter)||large cell size (5-100um diameter)|
|3 main shapes||animals, plants, fungi and protists|
|many environments||restricted environments|
Viruses are not classified, are very small (0.1-0.00001um cubed), are acellular, obligate intracellular parasites. Virion has virus genome surrounded by capsid/coat comprised of one or more proteins, may have an envelope (lipid and protein membrane acquired from the host cell in animal viruses). Viruses are classified by their type of nucleic acid, morphology (size, shape, symmetry of capsid), envelope presence or absence, host and disease produced. Capsid symmetry can be helical, icosahedral.
Bacteria and viruses are useful in the study of molecular biology as they are easy to grow and reproduce rapidly, have biological simplicity (contain less DNA than eukaryotes, replication of DNA, mechanisms of gene expression, haploid), have ease of manipulation (recombinant DNA technology, biotechnology)