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Microbial structure.

MD2001

QuestionAnswer
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).
Created by: robertspedding