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MD2001 Week 4 > Microbial Structure > Flashcards

Microbial Structure Flashcards

1
Q

What are the main features of prokaryotes? (7)

A
  • 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
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2
Q

What are the main features of eukaryotes? (7)

A
  • 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
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3
Q

What do prokaryotes and eukaryotes have in common?

A
  • plasma membrane
  • cytoplasm
  • DNA
  • ribosomes
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4
Q

How is DNA organised in prokaryotes?

A
  • no nucleus
  • nucleoid instead - no membrane
  • circular DNA
  • plasmids
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5
Q

How is DNA organised in eukaryotes?

A
  • double membrane bound nucleus
  • linear DNA
  • DNA organised into chromosomes, complexed with proteins
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6
Q

What are ribosomes like in prokaryotes?

A

70S ribosomes (smaller than ribosomes of eukaryotes)

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7
Q

What are ribosomes like in eukaryotes?

A

large complex ribosomes - many types of rRNA and proteins - 80S

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8
Q

Explain organelles of prokaryotes?

A

no membrane bound organelles independent of plasma membrane

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9
Q

Explain organelles of eukaryotes?

A

cytoplasm filled with large collection of complex organelles

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10
Q

Where does aerobic respiration occur in prokaryotes?

A

mesosomes - increase the surface of the plasma membrane - are used in aerobic respiration - site “cytoplasm”

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11
Q

Where does aerobic respiration occur in eukaryotes?

A

mitochondria with cristae

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12
Q

Explain DNA replication in prokaryotes?

A

transcription and translation occur simultaneously

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13
Q

Explain DNA replication in eukaryotes?

A

transcription requires the formation of mRNA and movement of mRNA from the nucleus to cytoplasm for translation

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14
Q

List the main structural components of bacteria? (6)

A
  • capsule
  • pili (fimbriae)
  • flagellae
  • spores
  • slime
  • cell wall
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15
Q

Structure of the capsule in bacterial cells?

A

loose polysaccharide structure

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16
Q

Function of the capsule in bacterial cells?

A
  • protects cell from phagocytosis

- protects cell from desiccation (loosing moisture in dry environments)

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17
Q

Structure of pili?

A
  • oligomeric proteins
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18
Q

Function of pili?

A
  • 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
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19
Q

Function of fimbriae?

A
  • facilitates bacterial attachment to host surfaces

structure - longer and more of them than pili

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20
Q

Structure of flagellae?

A
  • 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
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21
Q

Function of flagellae?

A
  • organs of locomotion

- move towards nutrients or away from immune system

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22
Q

Structure of spores?

A
  • 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
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23
Q

Function of spores?

A

important for survival and dispersal

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24
Q

Structure of slime?

A
  • polysaccharide material

- secreted by some bacteria growing in biofilms (cells stuck together)

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25
Q

Function of slime?

A
  • protects against immune attack

- protects against eradication by antibiotics

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26
Q

What are the two classifications of bacteria in terms of cell walls?

A
  • gram positive
  • gram negative
    based on chemical and physical properties of cell wall
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27
Q

What makes a cell wall gram positive?

A
  • two layers - thick PGN layer, cytoplasmic membrane

- LTA lipoteichoic acid

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28
Q

What makes a cell wall gram negative?

A
  • 3 layers - outer membrane, thin PGN (peptidoglycan) inside periplasmic space, cytoplasmic membrane
  • LPS lipopolysaccharide
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29
Q

What is PGN?

A

peptidoglycan

  • polymer of sugars and amino acids
  • forms mesh like layer outside plasma membrane
  • sugar component = alternating residues of N-acetylglucosamine + N-acetlymuramic acid
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30
Q

What is LTA

A

lipoteichoic acid

  • complex of trichroic acid + lipids
  • provides cell rigidity
  • recognised by host immune cells
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31
Q

What is LPS

A

lipopolysaccharide

  • in gram negative bacteria
  • essential for function of outer membrane
  • elicits potent immune and inflammatory host responses
  • produces endotoxins
32
Q

What are the outer membrane proteins?

A
  • lipoproteins and porins

- not endotoxins but contribute to virulence

33
Q

Why is the cell wall of bacteria important?

A

its what the immune system first recognises - this can trigger responses
also important for cell structure

34
Q

How do bacteria reproduce?

A

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
35
Q

What are the consequences of slow replicating bacteria in medicine?

A
  • harder to detecting diagnose

- harder to treat with antibiotics (since antibiotics usually attack what allows cell to divide and grow)

36
Q

What are the 4 phases of bacterial growth?

A
  • lag
  • log/exponential
  • stationary
  • death
37
Q

Lag phase?

A
  • period of active growth (in size not number)

- bacteria prepare for reproduction - synthesising DNA and enzymes for cell division

38
Q

Log/exponential phase?

A
  • cells divide at maximum rate
  • uniform replication
  • graph line is almost straight
39
Q

Stationary phase?

A
  • 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
40
Q

Death phase?

A
  • number of dying cells exceeds the number of newly born cells and so the number of viable cells starts to decline
41
Q

What are the processes of bacterial recombination?

A
  • conjugation
  • transformation
  • transduction
42
Q

What happens in conjugation?

A
  • one bacterium connects itself to another through the pilus

- genes are transferred from one bacterium to the other through this tube

43
Q

What happens in transformation?

A
  • some bacteria are capable of taking up DNA from their environment
44
Q

What happens in transduction?

A
  • involves the exchanging of bacterial DNA through bacteriophages (virus that infects bacteria)
45
Q

How can bacteria be classified?

A
  • gram stain - positive, negative
  • cell shape - cocci, bacilli, helical, spiral
  • atmospheric preference - aerobic, anaerobic, microaerophilic (growth)
  • key enzymes
  • fastidiousness
46
Q

What is a virus?

A
  • 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
47
Q

What are the structural components of a virus?

A
  • nucleic acid (DNA or RNA) (double or single)
  • capsid
  • envelope
  • spikes
48
Q

What is the capsid?

A
  • protein coat
  • composed of protein subunits - capsomeres
  • capsomeres consist of aggregated protomeres
  • various shapes of capsids - rod like, polyhedral, complex
49
Q

What is the envelope?

A

amorphous (no clear shape or form) surrounding SOME viruses

- composed of lips, protein and carbohydrate

50
Q

What are spikes?

A
  • glycoprotein projections arising from envelope
  • highle antigenic
  • may have enzymatic, adsorption or haemagglutin activity
  • often have a function related to binding to target cells
51
Q

What are the 6 steps of viral replication?

A
  • adsorption
  • penetration
  • replication
  • assembly
  • maturation
  • release of naked viruses or enveloped viruses
52
Q

What happens in adsorption?

A
  • virus binds to host cell

- highly specific to certain types of cell

53
Q

What happens in penetration?

A
  • virus injects genome into host cell - occurs by fusion, binding, ingestion
54
Q

What happens in replication?

A
  • capsid digested by proteolytic enzymes

- viral genome replicates using hosts cellular machinery

55
Q

What happens in assembly?

A
  • viral components and enzymes are produced and begin to assemble
56
Q

What happens in maturation?

A
  • virus fully develops
57
Q

What happens in release of naked viruses?

A
  • 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
58
Q

What happens in release of enveloped viruses?

A
  • 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
59
Q

What are protozoa?

A

single cell eukaryotes

60
Q

How are protozoa classified?

A
  • sporozoa
  • flagellates
  • amoeba
  • ciliates
61
Q

What are sporozoa?

A

intracellular parasites

62
Q

What are flagellates?

A

posses tail-like structures for mobility

63
Q

What are amoeba?

A

use temporary cell-body projections (pseudopods)

64
Q

What are ciliates?

A

move by beating multiple hair-like structures (cilia)

65
Q

List common protozoal infections?

A

malaria (plasmodium falciparum), giardiasis (guardia lamblia) “food poisoning”, toxoplasmosis (toxoplasma gondii), cryptosporidiosis (cryptosporidium parvum)

66
Q

What are fungi?

A
  • eukaryotic
  • multinucleate or multicellular
  • part of normal microbiota as well as being pathogens
67
Q

What are yeast?

A

single cell fungi - can form multicellular structures

68
Q

Structure of fungi?

A
  • thick carbohydrate wall containing chitin and gluons
  • usually grow as thread like filaments (hyphae)
  • multinucleate or multicellular
69
Q

How do yeast reproduce?

A
  • asexually - by budding - and occasionally binary fission
70
Q

What are fungal infections known as?

A

mycoses

71
Q

What are helminths?

A
  • parasitic worms
72
Q

What are the three groups of helminths found in humans?

A
  • Cestoda
  • trematoda
  • Nematoda
73
Q

What are Cestoda?

A

tapeworms

74
Q

What are Trematoda?

A

flukes

75
Q

What are Nematoda?

A

roundworms

76
Q

Where in the body are helminths usually found?

A

intestine

77
Q

How do helminths transmit?

A
  • via intermediate host
  • fecal-oral route
  • active skin penetration
  • injection by blood sucking insect “vector”

MD2001 Week 4 (10 decks)

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