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Microbial structure.
MD2001
Question | Answer |
---|---|
What is a mesosome? | An organelle of bacteria that appears as an invagination of the plasma membrane and functions either in DNA replication and cell division or excretion of exoenzymes. |
What are the structural components of bacteria? | Capsule, pili, flagellae, spores, slime and cell wall. |
What is the structure of the capsule? | Loose polysaccharide structure. |
What is the function of the capsule? | Protects the cell from phagocytosis and protects the cell from desiccation. |
What is the structure of the pili? | Composed of oligomeric pilin proteins. |
What is the function of the pili? | Appendage used for bacterial conjugation and forms a bridge that enable transfer of plasmids between bacteria. |
What is the structure of fimbriae? | May contain lectins which recognise oligosaccharide units on host cells. |
What is the function of fimbriae? | Facilitates bacterial attachment to host cells. |
What is the structure of the flagellum? | Organs of locomotion, composed of flagellin protein. 20nm-thick helical hollow tube. Driven by rotary engine at anchor point on inner cell membrane. |
What is a spore? | Metabolically inert form triggered by adverse environmental conditions. |
What adaptations do spores have? | Adapted for long-term survival allowing regrowth under suitable conditions. Hard, multi-layered coats making spore difficult to kill. |
Which bacteria causes botulism? | Clostridium botulinum. |
What causes gas gangrene? | Clostridium perfringes. |
What causes tetanus? | Clostridium tetani. |
What causes food poisoning? | Clostridium perfringes? |
What causes anthrax? | Bacillus anthracis. |
What is the structure and origin of slime? | Structure: polysaccharide material. Secreted by some bacteria growing in biofilms. |
What is the function of slime? | Protects against immune attack. Protects against eradication by antibiotics. |
How can you differentiate between bacterial cells? | Gram staining differentiates bacterial species into 2 groups: gram positive and gram negative. |
What are the four steps of gram staining? | Primary stain (crystal violet dye), trapping agent (Gram's iodine), decolourisation (alcohol) and counterstain (safranin). |
What does the gram positive test show about the cell wall? | 2 layers: thick PGN layer, cytoplasmic membrane and lipoteichoic acid. |
What does the gram negative test show about the cell wall? | 3 layers: outer membrane, thin peptidoglycan layer, cytoplasmic membrane and lipopolysaccharide. |
What are the main cell wall components? | Peptidoglycan, lipoteichoic acid, lipopolysaccharide and outer membrane proteins. |
What is peptidoglycan? | Polymer of sugars and AAs. Forms mesh-like layer outside plasma membrane. |
What is the sugar component of peptidoglycan? | Alternating residues of N-acetylglucosamine+N-acetylmuramic acid. |
What is lipoteichoic acid? | Complex of teichoic acid+lipids. Provides cell rigidity and are recognised by host immune cells. |
What is lipopolysaccharide? | Essential for function of outer membrane. Elicits potent immune and inflammatory host responses. Produces endotoxins. |
What is outer membrane proteins? | Lipoproteins and porins. Not endotoxins but do contribute virulence. |
What is the bacterial growth cycle? | During active growth, the number of cells continuously doubles at specific time intervals. |
What are the four phases of bacterial growth? | Lag phase, log phase, stationary phase and death or decline phase. |
What is the lag phase? | Represents the period of active growth (in size). Bacteria prepare for reproduction (i.e. synthesising DNA and enzymes for cell division). |
What is the log phase? | Cells divide at maximum rate. Uniform replication and graph line is almost straight. |
What is the stationary phase? | Cessation of growth, exhaustion of nutrients. Accumulation of inhibitory end products of metabolism or oxygen availability. |
What is the cell growth rate in the stationary phase? | Number of cells dying balances the number of new cells, so population stabilises. |
What happens in the death phase? | Number of dying cells starts to exceed the number of newly born cells and so the number of viable cells starts to decline. |
What is conjugation? | One bacterium connects itself to another through the pilus. Genes are transferred from one bacterium to the other through this tube. |
What is transformation? | Some bacteria are capable of taking up DNA from their environment. |
What is transduction? | Involves the exchanging of bacterial DNA through bacteriophages. |
What are the phases of bacterial recombination? | Conjugation, transformation and transduction. |
How are bacteria classified? | Gram stain, cell shape, atmosphere preference, key enzymes and fastidiousness. |
What are the different cell shapes of bacteria? | Cocci, bacilli and helical/spiral. |
What are the different atmospheric preferences of bacteria? | Aerobic, anaerobic and microaerophilic. |
What does a virus contain? | Only contains the parts needed to enter and control a host cell. |
What are the viral structural components? | Nucleic acid, capsid, envelope and spikes. |
What is the structure of the viral capsid? | Protein coat/shell, composed of protein subunits (capsomeres). |
What are capsomeres? | Consist of aggregated protomeres. |
What are the shapes of capsids? | Rod-like, polyhedral and complex. |
What is the viral envelope? | Amorphous structure surrounding some viruses. |
What is the viral envelope made of? | Composed of lipid, protein and carbohydrate. |
What are the viral spikes? | Glycoprotein projections arising from envelope. Highly antigenic. May have enzymatic, adsorption or haemagglutinin activity. |
How do viruses replicate? | Use hosts cellular machinery to replicate and produces many progeny which leave host to infect other cells in the organism. |
What are the steps of viral replication? | Adsorption, penetration, replication, assembly, maturation and release. |
What happens in adsorption? | Virus binds to host cell. Highly specific. |
What happens during penetration? | Virus injects its genome into host cell. Occurs by: fusion, binding and ingestion. |
What happens in viral replication? | Capsid digested by proteolytic enzymes. Viral genome replicates using the host's cellular machinery. |
What happens in assembly? | Viral components and enzymes are produced and begin to assemble. |
What happens in maturation? | Virus fully develops. |
What happens during viral release? | Occurs at the site of nucleic acid replication. Viral enzymes break down bacterial cell wall. |
When are RNA viruses released? | As they are produced. |
When are DNA viruses expelled from the host cell? | As cells autolyse and in inclusion bodies. |
How are enveloped viruses released? | Viruses migrate to either plasma or nuclear membrane. Envelopes formed around nucleocapsids by budding of cell membrane. Slow continuous release of mature viral particles. No inclusion bodies. |
What are the classifications of protozoa? | Sporozoa, flagellates, amoeba and ciliates. |
What are sporozoa? | Intracellular parasites. |
What are flagellates? | Possess tail-like structures for motility. |
What are amoeba? | Use temporary cell-body projections (pseudopods). |
What are ciliates? | Move by beating multiple hai r-like structures (cilia). |