Microbiology

• Flagella

  • Number and location in cell varies
  • 5-10/cell
  • 10-20 nm in diameter
• Fimbriae

  • thinner, shorter and more numerous 100-1000/cell and 2-8 nm in diameter.
• peptidoglycan carbohydrates backbone- a series of NAG (N- acetylglucosamine) and NAM (N- acetyl-muramic acid) with tetrapeptide side chain and peptide cross-links,
• Gram positive

  • 20-80 nm
• Endospore are formed under unfavourable condition and germinate under favourable condition- protect cells from stress

  • only present in gram + bacteria
  • Triggered by nutrient starvation and high cell density
• Prokaryotes are so dominant because they have a fast growth rate ( 13 minutes doubling time) and evolve/ adapt fast
• Batch culture assays measure the average behaviour of cells. No growth can mean that death rate and growth rate are in balance.
• Growth phase:

  • Catabolism- when food is broken down, energy is generated and building blocks are produced
  • The energy released during chemical bond braking is captured in ATP (the most common energy currency molecule)
• ·      Auxotrophy is common in nature and partially explains our inability to culture most microbes.
• Cross feeding also known as syntrophy is when one organism gains metabolic products from another organism.

  • It allows auxotroph to survive by harvesting resources generated by another species.
• Viruses are acellular microorganisms that cannot survive without a host; they have no metabolic activities of their own and rely completely on the biosynthetic machinery of the infected cell to multiply.
• Viruses are obligate intracellular parasites and infect ALL CELL TYPES.
• The viral capsid is a protein coat. Its function is to protect viral genome of virus.
• spike is critical for attachment and cell entry. It is also a main target for neutralising immunity. Hence, vaccines target spike to prevent attachment to cells.
• Sars-CoV-2 Replication

  A) Genome translation replication module only

  B) Spike binding to ACE2 receptor

  C) 2/3. Cell entry and fusion

  D) Viral RNA synthesis (transcription)

  E) 4. Viral mRNA & genome

  F) 4. Translation

  G) 5. Assembly

  H) 6. Exocytosis

  
• Antibiotic resistance:

  • consumption of livestock and grain treated with antibiotics significantly increase spread of resistance in bacteria.
  • Manure of eg chicken fed with antibiotics also contain antibiotic resistant bacteria and are used as fertiliser for grains.
• Structures that would contain a complete chromosome of a bacterium:

  • Nucleoid
  • endospore
• The largest number of viable cells in a bacterial culture is found during the growth phase known as:

  • Stationary phase (largest)
• A characteristic of photoheterotrophic metabolism is:

  • dependence on organic carbon (CO2) for building blocks.
  • not fixed carbon or inorganic
•  Bacterial identification:

  • Identification of bacteria can be achieved
  • Many 16S rRNA sequences come from uncultivated bacteria.
  • Traditional microbiology focussed on pathogens and fast-growing bacteria. 
• The composition of the human microbiome is:

  • phylum poor but species rich
  • only 92 bacterial and 26 archaeal groups but many species and strains.
• Components of a bacteriophage:

  • Capsid head
  • Sheath
  • Tail fibre

  
• 1. Chemo-heterotroph: carbon source- organic compounds (fixed carbon), energy source- chemical compounds.
  2. Chemo-autotrophs: carbon source- CO2, energy source- chemical compounds.
• 1. Photo-heterotroph: Carbon source is organic compounds, energy source is solar.
  2. Photo-autotroph: carbon source is CO2, energy source is solar.
• Example of each trophism:

  1. Chemo-hetero: most animals, fungi, protozoa and bacteria
  2. Chemo-auto: sulfur, hyrogen, nitrifying bacteria, some archaea
  3. Photo-hetero: green and purple non-sulfur bacteria, some archaea.
  4. Photo-auto: plants, algae, cyanobacteria ( ancestor of chloroplast)
• Axis labels:

  • X: time
  • Y: number of micro-organism or intensity of signs or symptoms

  
• Selection pressure the HIV is under within an individual patient:

  • Advent of resistance: HART (highly active retroviral therapy.
  • Immune response of patient: Virus responds through rapid mutation and evolution. The virus evolves to evade immune surveillance, leading to the emergence of viral variants that are less susceptible to immune-mediated clearance.
• Viruses in each individual tissue are more closely related to each other than they are to viruses from other tissues.

  • Relatedness = Single viruses infect individual tissues and then remain in those tissues where they evolve.

  
• Selection pressures; (HIV)

  • Immune System
  • Drug Regimen
  • Changes in receptor
  • Tropism in tissues
•  

  Bacteriophage attaches to surface of bacterial cell, tail sheath contracts injecting phage DNA into the cell. Phage DNA and proteins synthesised, then self-assemble to form phage heads, tails and tail fibres. Phage directs production of an enzyme that damages bacterial cell wall allowing fluid to enter which bursts the cell releasing large numbers of phage particles.
• (A)RNA polymerase begins transcribing DNA doesn't need a short RNA primer.
• Possible consequences of a DNA mutation in non-coding gene regions?  

  The gene product is not expressed as it should be, i.e. the protein is not produced as normal - there may be no protein produced; there may be too little protein or too much protein produced).
• List FOUR factors that may alter the basic phenotypic inheritance patterns that were observed by Mendel.           (2 marks)

  Incomplete dominance, Co-dominance, Polygenic traits, Environment, Linked genes, Sex-linked genes.