Microbes 1 Flashcards
What are the 2 main divisions of microbes?
- Prokaryotes
2. Eukaryotes
What are the 2 domains within prokaryotes?
- Archaea
2. Bacteria
What are the 4 kingdoms within eukaryotes?
- Protista
- Fungi
- Plantae
- Animalia
What are 3 differences between prokaryotes and eukaryotes?
- Prokaryotes have no discrete organelles
- Prokaryotes have no nucleus
- Prokaryotes have DNA with circular genome
What is Koch’s 1st Postulate?
The microorganism should be isolated from all cases of a specific disease but should not be found in healthy individuals
What is Koch’s 2nd Postulate?
The microorganism should be isolated from the diseased individual and grown in a pure culture on an artificial medium
What is Koch’s 3rd Postulate?
The microorganism should reproduce the specific disease when inoculated into a healthy person
What is Koch’s 4th Postulate?
The microorganism should be re-isolated in pure culture from the experimental infection
What is a potential limitation of Koch’s Postulated?
Healthy individuals may possess some levels of a microorganism but not enough to make them unhealthy
Name 5 main types of pathogenic organisms
- Bacteria
- Viruses
- Fungi
- Protozoa and Helminths
- Prions
Describe the cell wall of gram-positive bacteria
Thick, peptidoglycan layer containing lipoteichoic acid
Describe the cell wall of gram-negative bacteria
Thin, peptidoglycan layer containing lipopolysaccharide
Name 3 key differences between gram-positive and gram-negative bacteria
- Gram-positive cell wall has a thick peptidoglycan layer
- Gram positive cell wall has no LPS
- Gram negative cell wall has inner and outer membrane
What is the function of peptidoglycan in bacterial cell wall?
Cell wall strength obtained through cross links between adjacent strands through a pentapeptide bridge
What are the 2 main structural components of peptidoglycan?
- N-acetylglucosamine (NAG)
2. N-acetylmuramic acid (NAM)
What are the 3 components of LPS?
- Lipid A
- Core oligosaccharide
- O-polysaccharide or O-antigen
Name 2 functions of LPS
- Protect peptidoglycan from lysozyme
2. Impedes entry of antibiotics
What is cytoplasm?
Aqueous environment packed with biosynthetic machinery required for growth and cell division and the genetic material
What is a nucleoid?
Double helix of DNA arranged in supercoiled circular state
What are inclusion granules?
Storage products
What is the bacterial cell envelope?
Several layers of material which enclose the cytoplasm
What makes up a bacterial cell envelope?
Plasma membrane, cell wall and sometimes a capsule
What makes up a bacterial capsule?
Mainly polysaccharides
What are 3 functions of bacterial capsules?
- Protect against phagocytosis
- Complement lysis
- Important for adhesion to surfaces and biofilm formation
Give 2 examples of surface appendages on bacterial cells
- Flagella
2. Pili/Fimbriae
What are flagella?
Long, helical filaments extending from the cell surface
What is the function of flagella?
Enable movement
What are flagella made up of?
Protein subunits called flagellin
What is the function of pili?
Attachment to other bacteria or to host cells
On what type of bacteria are pili generally found on?
Gram negative
What is a bacterial spore?
Highly resistant resting phase, facilitating survival in adverse conditions
What is sporulation?
Process of a vegetative cell forming a spore
What is germination?
The process of a spore transforming into a vegetative cell
What are the 4 main ways to classify bacteria?
- Gram staining
- Morphology
- Respiration
- Shape/Reproduction
What are 3 minor ways to classify bacteria?
- Motility
- Spores
- Enzyme activity
What colour does gram negative bacteria stain?
Pink
What colour does gram positive bacteria stain?
Purple
What are the 2 main shapes of bacteria?
- Cocci (circle)
2. Bacilli (rods)
What are the two ways a bacterium can respire?
- Aerobically
2. Anaerobically
What are obligate anaerobe bacteria?
Bacteria which cannot live in the presence of oxygen
What are facultative anaerobe bacteria?
Bacteria which can live either in the presence or absence of oxygen
What are the two processes which bacteria use to produce energy?
- Respiration
2. Fermentation
How do bacteria reproduce?
Asexually by binary fission
How does replication of genes occur in bacteria?
- DNA helicase unwinds DNA stand by breaking H bonds
- DNA polymerase adds bases to leading strand in continuous fashion
- DNA polymerase adds bases to lagging strand in discontinuous fashion
What direction can DNA polymerase add bases?
3’ to 5’
What is the name of the replication mechanism of bacterial DNA?
Semi conservative
Name 2 ways changes can occur in bacterial genome
- Mutation
2. Recombination
What is a mutation?
Changes in DNA nucleotide sequence
What are 4 types of mutation?
- Point mutations
- Deletions
- Insertions
- Inversions
What is recombination?
Rearrangement of DNA involving breaking and re-joining of 2 homologous DNA double helices
Name 2 extrachromosomal elements of bacteria
- Plasmids
2. Bacteriophages
What is an extrachromosomal element?
Small, independently replicating nucleic acid molecules
What are plasmids?
Small replicating circular units of double stranded DNA
What can larger plasmids offer to a bacteria?
Can carry genes conferring phenotypic advantage-resistance to antimicrobials
What are bacteriophages?
Bacterial viruses that can survive inside and out bacterial cells
What are 4 methods of genetic transfer in bacteria?
- Transformation
- Transduction
- Conjugation
- Transposition
What is transformation?
Naked DNA released following lysis of a bacterial cell wall, which is recombined with recipient cell chromosomal DNA
What is transduction?
Transfer of genetic material by infection with a bacteriophage
What is conjugation?
A sex pilus allows cell to cell contact for DNA contact (only between closely related species)
What is transposition?
DNA sequences jump from a site in one DNA molecule to another cell
