Microbial Structure Flashcards
What are the main features of prokaryotes? (7)
- no nucleus - nucleoid instead - no membrane present
- circular DNA
- plasmids
- 70s ribosomes
- no membrane bound organelles independent of plasma membrane
- mesosomes used in aerobic respiration
- transcription and translation occur simultaneously
What are the main features of eukaryotes? (7)
- true nucleus - bound by a double membrane
- linear DNA
- DNA organised into chromosomes complexed with proteins
- large complex ribosomes with many types of rRNA and proteins
- cytoplasm filled with large complex collection of organelles
- mitochondria with cristae - aerobic respiration
- transcription requires formation of mRNA and movement of mRNA from nucleus to cytoplasm for translation
What do prokaryotes and eukaryotes have in common?
- plasma membrane
- cytoplasm
- DNA
- ribosomes
How is DNA organised in prokaryotes?
- no nucleus
- nucleoid instead - no membrane
- circular DNA
- plasmids
How is DNA organised in eukaryotes?
- double membrane bound nucleus
- linear DNA
- DNA organised into chromosomes, complexed with proteins
What are ribosomes like in prokaryotes?
70S ribosomes (smaller than ribosomes of eukaryotes)
What are ribosomes like in eukaryotes?
large complex ribosomes - many types of rRNA and proteins - 80S
Explain organelles of prokaryotes?
no membrane bound organelles independent of plasma membrane
Explain organelles of eukaryotes?
cytoplasm filled with large collection of complex organelles
Where does aerobic respiration occur in prokaryotes?
mesosomes - increase the surface of the plasma membrane - are used in aerobic respiration - site “cytoplasm”
Where does aerobic respiration occur in eukaryotes?
mitochondria with cristae
Explain DNA replication in prokaryotes?
transcription and translation occur simultaneously
Explain DNA replication in eukaryotes?
transcription requires the formation of mRNA and movement of mRNA from the nucleus to cytoplasm for translation
List the main structural components of bacteria? (6)
- capsule
- pili (fimbriae)
- flagellae
- spores
- slime
- cell wall
Structure of the capsule in bacterial cells?
loose polysaccharide structure
Function of the capsule in bacterial cells?
- protects cell from phagocytosis
- protects cell from desiccation (loosing moisture in dry environments)
Structure of pili?
- oligomeric proteins
Function of pili?
- sex structure - for DNA transfer - “bacterial conjugation” - tube forms which allows the transfer of plasmids between bacteria
- highly antigenic (avoids detection by altering surface proteins)
- plays role in host attachment
Function of fimbriae?
- facilitates bacterial attachment to host surfaces
structure - longer and more of them than pili
Structure of flagellae?
- composed of flagellin protein
- 20nm thick
- helical hollow tube
- driven by rotary engine at anchor point on inner cell membrane
- cells can have one or many
Function of flagellae?
- organs of locomotion
- move towards nutrients or away from immune system
Structure of spores?
- hard multi-layered coats - making spore difficult to kill
- adapted for long term survival allowing regrowth under suitable conditions
- metablolically inactive form - but triggered by adverse environmental conditions
Function of spores?
important for survival and dispersal
Structure of slime?
- polysaccharide material
- secreted by some bacteria growing in biofilms (cells stuck together)
Function of slime?
- protects against immune attack
- protects against eradication by antibiotics
What are the two classifications of bacteria in terms of cell walls?
- gram positive
- gram negative
based on chemical and physical properties of cell wall
What makes a cell wall gram positive?
- two layers - thick PGN layer, cytoplasmic membrane
- LTA lipoteichoic acid
What makes a cell wall gram negative?
- 3 layers - outer membrane, thin PGN (peptidoglycan) inside periplasmic space, cytoplasmic membrane
- LPS lipopolysaccharide
What is PGN?
peptidoglycan
- polymer of sugars and amino acids
- forms mesh like layer outside plasma membrane
- sugar component = alternating residues of N-acetylglucosamine + N-acetlymuramic acid
What is LTA
lipoteichoic acid
- complex of trichroic acid + lipids
- provides cell rigidity
- recognised by host immune cells
What is LPS
lipopolysaccharide
- in gram negative bacteria
- essential for function of outer membrane
- elicits potent immune and inflammatory host responses
- produces endotoxins
What are the outer membrane proteins?
- lipoproteins and porins
- not endotoxins but contribute to virulence
Why is the cell wall of bacteria important?
its what the immune system first recognises - this can trigger responses
also important for cell structure
How do bacteria reproduce?
by binary fission - asexual
- genetic information which is found in circular DNA is distributed equally between each daughter cell
- DNA is self replicating and makes a copy of itself before cell division
- “bi-directional” replication of circular DNA- replicates in 2 directions
What are the consequences of slow replicating bacteria in medicine?
- harder to detecting diagnose
- harder to treat with antibiotics (since antibiotics usually attack what allows cell to divide and grow)
What are the 4 phases of bacterial growth?
- lag
- log/exponential
- stationary
- death
Lag phase?
- period of active growth (in size not number)
- bacteria prepare for reproduction - synthesising DNA and enzymes for cell division
Log/exponential phase?
- cells divide at maximum rate
- uniform replication
- graph line is almost straight
Stationary phase?
- growth stops
- exhaustion of nutrients
- accumulation of inhibitory end products of metabolism or oxygen availability
- number of cells dying balances the number of new cells, so population stabilises
Death phase?
- number of dying cells exceeds the number of newly born cells and so the number of viable cells starts to decline
What are the processes of bacterial recombination?
- conjugation
- transformation
- transduction
What happens in conjugation?
- one bacterium connects itself to another through the pilus
- genes are transferred from one bacterium to the other through this tube
What happens in transformation?
- some bacteria are capable of taking up DNA from their environment
What happens in transduction?
- involves the exchanging of bacterial DNA through bacteriophages (virus that infects bacteria)
How can bacteria be classified?
- gram stain - positive, negative
- cell shape - cocci, bacilli, helical, spiral
- atmospheric preference - aerobic, anaerobic, microaerophilic (growth)
- key enzymes
- fastidiousness
What is a virus?
- an infective agent
- a nucleic acid molecule in a protein coat
- is able to multiply only within living cells of a host
- can infect all cell types
- DNA or RNA
- too small to be seen by light microscopy
What are the structural components of a virus?
- nucleic acid (DNA or RNA) (double or single)
- capsid
- envelope
- spikes
What is the capsid?
- protein coat
- composed of protein subunits - capsomeres
- capsomeres consist of aggregated protomeres
- various shapes of capsids - rod like, polyhedral, complex
What is the envelope?
amorphous (no clear shape or form) surrounding SOME viruses
- composed of lips, protein and carbohydrate
What are spikes?
- glycoprotein projections arising from envelope
- highle antigenic
- may have enzymatic, adsorption or haemagglutin activity
- often have a function related to binding to target cells
What are the 6 steps of viral replication?
- adsorption
- penetration
- replication
- assembly
- maturation
- release of naked viruses or enveloped viruses
What happens in adsorption?
- virus binds to host cell
- highly specific to certain types of cell
What happens in penetration?
- virus injects genome into host cell - occurs by fusion, binding, ingestion
What happens in replication?
- capsid digested by proteolytic enzymes
- viral genome replicates using hosts 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 in 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 the host cell - as cells autolyse - in inclusion bodies
What happens in 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 cell eukaryotes
How are protozoa classified?
- sporozoa
- flagellates
- amoeba
- ciliates
What are sporozoa?
intracellular parasites
What are flagellates?
posses tail-like structures for mobility
What are amoeba?
use temporary cell-body projections (pseudopods)
What are ciliates?
move by beating multiple hair-like structures (cilia)
List common protozoal infections?
malaria (plasmodium falciparum), giardiasis (guardia lamblia) “food poisoning”, toxoplasmosis (toxoplasma gondii), cryptosporidiosis (cryptosporidium parvum)
What are fungi?
- eukaryotic
- multinucleate or multicellular
- part of normal microbiota as well as being pathogens
What are yeast?
single cell fungi - can form multicellular structures
Structure of fungi?
- thick carbohydrate wall containing chitin and gluons
- usually grow as thread like filaments (hyphae)
- multinucleate or multicellular
How do yeast reproduce?
- asexually - by budding - and occasionally binary fission
What are fungal infections known as?
mycoses
What are helminths?
- parasitic worms
What are the three groups of helminths found in humans?
- Cestoda
- trematoda
- Nematoda
What are Cestoda?
tapeworms
What are Trematoda?
flukes
What are Nematoda?
roundworms
Where in the body are helminths usually found?
intestine
How do helminths transmit?
- via intermediate host
- fecal-oral route
- active skin penetration
- injection by blood sucking insect “vector”
