Microbial Structure Flashcards
What is the difference in the genetic material of eukaryotes vs prokaryotes concerning nuclei?
Eukaryotes:
- has true nucleus; bound by double membrane
Prokaryotes:
- no nucleus; has a nucleoid; no physical boundary
What is the difference in the genetic material of eukaryotes vs prokaryotes concerning DNA?
Eukaryotes:
- linear DNA
- organised into chromosomes; complexes with proteins
Prokaryotes:
- circular DNA
- DNA “naked”; plasmids present
What is the difference in the genetic material of eukaryotes vs prokaryotes concerning ribosomes?
Eukaryotes:
- large complex ribosomes with many types of rRNA & proteins
Prokaryotes:
-70S ribosomes
What is the difference in structure between eukaryotes and prokaryotes concerning membrane bound organelles?
Eukaryotes:
+ Cytoplasm filled with large complex collection of membrane bound organelles
Prokaryotes:
+ No membrane bound organelles independent of plasma membrane
Which type of cells have mitochondria and what are they?
Eukaryotes - mitochondria with cristae are “energy centres”
Which type of cells have mesomes and what are they?
Prokaryotes - mesomes are used in aerobic respiration, cell division, DNA replication
What are the structural components of bacteria?
\+ Capsule \+ Pili (fimbriae) \+ Flagellae \+ Spores \+ Slime \+ Cell wall
What are features/properties of the bacteria capsule?
+ Loose polysaccharide structure
+ Protects cell from phagocytosis
+ Protects cells from dessication
What are features/properties of pili?
+ Singular = pilus “hair”
+ Composed of oligomeric pilin proteins
+ Appendage used for bacterial conjugation
+ Forms tube/bridge to enable transfer of plasmids between bacteria
+ Highly antigenic
+ Plays role in attachment
What are the features/properties of fimbriae?
+ Singular = fimbria “thread”
+ Not on all bacteria
+ May contain lectins which recognise oligosaccharide units on host cells
+ Facilitates bacterial attachment to host surfaces
What are the features/properties of flagellae?
+ Singular = flagellum “whip”
+ Organs of locomotion
+ Single/multiple
+ Composed of flagellin protein
+ 20nm-thick helical hollow tube
+ Driven by rotary engine at anchor point on inner cell membrane
What are the features/properties of spores?
+ Metabolically inert form triggered by adverse environmental conditions
+ Adapted for long-term survival allowing regrowth under suitable conditions
+ Hard, multi-layered coats making spore difficult to kill
What are some common diseases caused by sporing bacteria?
\+ Botulism \+ Gas gangrene \+ Tetanus \+ Food poisoning \+ Anthrax
What sporing bacteria causes botulism?
Clostridium botulinum
What sporing bacteria causes gas gangrene?
Clostridium perfringens
What sporing bacteria causes tetanus?
Clostridium tetani
What sporing bacteria causes food poisoning?
Clostridium perfringens
What sporing bacteria causes anthrax?
Bacillus anthracis
What are the features/properties of slime?
+ Polysaccharide material
+ Secreted by some growing bacteria in biofilms
+ Protects against immune attack
+ Protects against eradications by antibiotics
What is Gram staining?
+ Based on chemical and physical properties of the cell walls
+ Differentiates bacterial species into 2 groups:
- Gram positive (+)
- Gram negative (-)
What are the 4 steps involved in Gram staining?
- Primary stain
- Trapping agent
- Decolourisation
- Counterstain
What is involved in step 1: Primary stain?
Cresyl violet dye stains all the bacterial cells purple
What is involved in step 2: Trapping agent?
+ Gram’s iodine is used
+ Forms CVI complexes in cell wall (larger than CV so not to be easily washed out of the PGN layer)
What is involved in step 3: Decolourisation?
+ Alcohol/acetone is utilised
+ Interacts with lipids in cell wall
What happens during decolourisation if the bacterial is Gram negative?
+ Loses outer LPS layer
+ Exposes thin inner PGN layer
+ Coloured complexes mainly wash away
What happens during decolourisation if the bacteria is Gram positive?
+ Becomes dehydrated and traps the complexes in thicker PGN layer of cell wall
What is involved in step 4: Counterstain?
The dye safranin is used
What colour is the cell if it is Gram negative?
Pink/reddish
What colour is the cell is it is Gram positive?
Purple
What does PGN stand for?
Peptidoglycan
What does LPS stand for?
Lipopolysaccharide
What does LTA stand for?
Lipoteichoic acid
What are the cellular differences in Gram positive and Gram negative regarding layers of the cell?
Gram positive:
+ 2 layers
- thick PGN layer
- cytoplasmic membrane
Gram negative: \+ 3 layers - outer membrane - thin PGN layer (inside periplasmic space) - cytoplasmic membrane
What are the differences in cell wall components between Gram positive and Gram negative?
Gram positive: LTA
Gram negative: LPS
What are the different cell wall components?
+ Peptidoglycan (PGN; murein)
+ Lipoteichoic Acid (LTA)
+ Lipopolysaccharide (LPS)
+ Outer Membrane Proteins (OMPs)
What are the features of peptidoglycans?
+ Comprised from polymers of sugars and amino acids
+ Forms mesh-like layer outside plasma membrane
+ Sugar component = alternating residues of N-acetylglucosamine + N-acetylmuramic acid
What are the features of lipoteichoic acids?
+ Complex of lipoteichoic acid and lipids
+ Provides cell rigidity
+ Recognised by host immune cells
What are the features of lipopolysaccharides (Gram -ve)?
+ Essential for function of outer membrane
+ Elicits potent immune and inflammatory host responses
+ Produces endotoxins
What are the features of outer membrane proteins?
+ Consist of lipoproteins & porins
+ Not endotoxins but do contribute to virulence
Features of bacterial replication of genome
+ Reproduce by binary fission (asexual)
- 1 cell reproduces to give 2 daughter cells
+ Genetic information found in circular DNA
- distributed equally between each daughter cell
+ DNA is a self-replicating molecule
- can make an exact copy of itself before cell division
+ Circular DNA; replication starts at ‘origin’
- replicates in 2 directions (bi-directional replications)
- 2 replication forks split off from origin and meet at bottom
What are features of the bacterial growth cycle?
+ During active growth, the number of cells continuously doubles at specific time intervals
+ Each binary fission takes a specific duration of time (depends on bacterium)
+ 1=21 =22=23 =24 =25 =26 …2n n = number of generations
What are the 4 bacterial growth phases?
+ Lag
+ Log/exponential
+ Stationary
+ Death
What happens in the Lag Phase (1)?
+ Represents the period of active growth (i.e in size, not number)
+ Bacteria prepare for reproduction i.e synthesising DNA and enzymes for cell division
What happens in the Log/Exponential Phase (2)?
+ Cells divide at maximum rate
+ Uniform cell replication
+ Graph line is almost straight (vertical)
What happens during the Stationary Phase (3)?
+ Cessation of growth
+ Exhaustion of nutrients
+ Accumulation of inhibitory end products of metabolism or oxygen availability
+ Number of cells dying balances the number of new cells so the population stabilises
What happens during the Death Phase (4)?
+ Number of dying cells starts to exceed the number of newly born cells so the number of viable cells starts to deline
Due to what characteristics are bacteria classified/identified?
+ Gram stain: positive/negative
+ Cell shape: cocci; bacilli; helical/spiral
+ Atmosphere preference: aerobic; anaerobic; michroaerophilic
+ Key enzymes
+ Fastidiousness
What shape are ‘cocci’ bacteria?
Spherical
What shape are ‘bacilli’ bacteria?
Rod-shaped
What shape are ‘spiral’ bacteria?
Helical rod
Which bacteria are Gram positive?
+ Staphylococcus aureus
+ Listeria monocytogenes
What are the structural components of viruses?
+ Nucleic acid
+ Capsid
+ Envelope
+ Spikes
What types of nucleic acid might be involved as a structural component of viruses?
+ ds DNA
+ ss DNA
+ ds RNA
+ ss RNA
What are the features of Capsids?
+ Protein coat/shell
+ Composed of protein subunits (capsomeres)
+ Capsomeres consist of aggregated protomeres
+ Various shapes of caspids
- rod-like
- polyhedral
- complex
What are the features of an envelope?
+ Amorphous structure surrounding some viruses
+ Composed of lipid, protein & carbohydrate
What are the features of spikes?
+ Glycoprotein projections arising from envelope
+ Highly antigenic
+ May have enzymatic, adsorption or haemagglutin activity
What are features of viruses?
+ Intracellular obligate parasites
+ Uses host’s cellular machinery to replicate
+ Produces many progeny which leave host to infect other cells in the organism
+ May infect any type of cell
- animal
- plant
- bacterial
What are the 6 steps in viral replication?
- Adsorption
- Penetration
- Replication
- Assembly
- Maturation
- Release
Step 1 - Adsorption:
+ Virus binds to host cell
+ Highly specific
Step 2 - Penetration:
+ Virus injects its genome into host cell
+ Occurs by:
- fusion
- binding
- ingestion
Step 3 - Replication:
+ Capsid digested by proteolytic enzymes
+ Viral genome replicates using host’s cellular machinery
Step 4 - Assembly:
+ Viral components and enzymes are produced and begin to assemble
Step 5 - Maturation:
+ Virus fully develops
Step 6 - Release of Naked Viruses
+ Occurs at site of nucleic acid replication
+ Viral enzymes break down bacterial cell wall
+ RNA viruses released as they are produced
+ DNA viruses expelled from host cell:
- as cells autolyse
- in inclusion bodies
Step 6 - Release of Enveloped Viruses
+ Viruses migrate to either plasma membrane or nuclear membrane
+ Envelopes formed around nucleocapsids by “budding” of cell membrane
+ Slow continuous release of mature viral particles
+ No inclusion bodies
What are protozoa?
Single celled eukaryotes
What are the different classifications of protozoa?
+ Sporozoa: intracellular parasites
+ Flagellates: possess tail-like structures for motility
+ Amoeba: use temporary cell-body projections (pseudopods)
+ Ciliates: move by beating multiple hair-like structures (cilia)
Name some common protozoal infections:
+ Malaria
+ Giardiasis
+ Toxoplasmosis
+ Cryptosporidiosis
What protozoa causes Malaria?
Plasmodium falciparum
What protozoa causes Giardiasis?
Giardia lamblia
What protozoa causes Toxoplasmosis?
Toxoplasma gondii
What protozoa causes Cryptosporidiosis?
Cryptosporidium parvum
What are features of fungi?
+ Eukaryotic
+ Multinucleate or multicellular organisms
+ Yeasts are single-celled
+ Thick carbohydrate wall containing chitin and glucans
+ usually grow as thread-like filaments (hyphae)
+ Reproduce asexually by budding, and occasionally by binary fission
+ Part of normal macrobiota as well as being pathogens
+ Fungal infections = “mycoses”
What are some common fungal infections?
+ Candidiasis
+ Cryptococcosis
+ Aspergillosis
+ Ringworm
What causes Candidiasis?
Candida Albicans (yeast)
What are features of Cryptococcosis?
+ Cryptococcus neoformans
+ Encapsulated yeast
+ Lab diagnosis by India Ink
+ Mainly treated with amphotericin B
+ Affects lungs or meninges
What are features of Aspergillosis?
+ Aspergillus flavus (yeast)
+ Production of aflatoxins
+ Spores inhaled
+ Immune response and hypersensitivity pneumonitis results
What are features of ringworm?
+ Tinea corporis (tinea pedis is athlete’s foot)
+ Skin infection
+ Affects scalp, skin, fingernails, toenails, feet
What are features of helminths?
+ 3 main groups important in humans
+ Infections most common in tropical/sub-tropical climates
+ Usually intestinal species
What are the 3 main groups of helminths?
+ Cestoda: tapeworms
+ Trematoda: flukes
+ Nematoda: roundworms
What are the transmission pathways of helminths?
+ Via intermediate host
+ Faeco-oral route
+ Active skin penetration
+ Injection by blood-sucking insect
What are features of the helminth: Schistosomiasis (bilharzia)?
+ Fluke (trematode)
+ Schisosoma haematobium, schistosoma mansoni, schistosoma japonica
+ Larval development in aquatic snails
+ Urinary & intestinal infections
What are features of the helminth: Trichiuriasis?
+ Nematode (roundworm)
+ Trichuris trichiuria
+ Human whipworm
+ Intestinal infection
What are features of the helminth: Tapeworm?
\+ Taenia solium \+ Acquired from ingesting worms or eggs in undercooked pork \+ Reside in large intestine \+ Can grow up to 7m long \+ Scolex (sucker/hooks) for attachment
