Bacterial Cell-Surface Structures

Cell-Surface Structures

• Bacterial cell walls have various structures involved in locomotion, attachment, and genetic material transfer.
• Flagella are responsible for locomotion of the cell.
• Fimbriae are involved in attachment to suitable surfaces or other individuals in a colony.
• Sex pili are responsible for transferring genetic material.

Prokaryote Nutritional and Metabolic Adaptations

• Prokaryotes can be categorized by how they obtain energy and carbon.
• Phototrophs obtain energy from light.
• Chemotrophs obtain energy from chemicals.
• Autotrophs require CO2 as a carbon source.
• Heterotrophs require an organic nutrient as a carbon source.
• Four major modes of nutrition are:
  • Photoautotrophy
  • Chemoautotrophy
  • Photoheterotrophy
  • Chemoheterotrophy

Archaea

• Archaea share certain traits with bacteria and other traits with eukaryotes.
• Some archaea are extremophiles, living in extreme environments.
• Examples of extremophiles include:
  • Extreme halophiles (living in highly saline environments)
  • Extreme thermophiles (thriving in very hot environments)
  • Methanogens (strict anaerobes that produce methane as a waste product)

Bacteria

• Bacteria include the vast majority of prokaryotes.
• Proteobacteria are gram-negative bacteria that include photoautotrophs, chemoautotrophs, and heterotrophs.
• Some proteobacteria are anaerobic, while others are aerobic.
• Cyanobacteria are photoautotrophs that generate O2.
• Chlamydias are parasitic bacteria that live within animal cells.
• Spirochetes are helical heterotrophs.
• Gram-positive bacteria include:
  • Actinomycetes (decomposing soil)
  • Some Staphylococcus and Streptococcus (pathogenic)
  • Mycoplasms (the smallest known cells)

Prokaryote Impact on Humans

• Prokaryotes have both beneficial and harmful impacts on humans.
• Some prokaryotes are human pathogens, while others have positive interactions with humans.
• Mutualistic bacteria:
  • Live in human intestines (about 500-1,000 species)
  • Break down undigested food
• Pathogenic bacteria:
  • Cause about half of all human diseases
  • Examples include Lyme disease
• Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxins.
• Exotoxins are secreted and cause disease even if the prokaryotes are not present.
• Endotoxins are released when bacteria die and their cell walls break down.

Structure of Viruses

• Viral genomes are classified as DNA or RNA viruses based on the type of nucleic acid.
• Viral genomes may consist of:
  • Double- or single-stranded DNA
  • Double- or single-stranded RNA
• Capsids are protein shells that enclose the viral genome.
• Capsids can have various structures depending on the type of virus.
• Capsids are built from protein subunits called capsomeres.
• Many complex capsids are found among bacteriophages.
• Phages are viruses that infect bacteria and have elongated capsid heads that enclose their DNA.
• A protein tail piece attaches the phage to the host and injects the phage DNA inside.
• Some viruses have membranous envelopes that help them infect hosts.
• Viral envelopes contain a combination of viral and host cell molecules.
• Examples of viruses with membranous envelopes include influenza viruses.