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MD2001 Week 4 lectures > Microbial structure > Flashcards

Microbial structure Flashcards

• Recognise the structural differences between eukaryotic and prokaryotic cells • Identify the main structural features of bacteria, viruses, protozoa, fungi, helminths, and yeasts. • Describe how bacteria and viruses replicate and how genetic information is transferred between bacterial cells.

1
Q

What are the 2 basic types of cells?

A
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2
Q

What do eukaryotic and prokaryotic cells have in common?

A
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3
Q

Differences in Genetic Material for prokaryotes and eukaryotes

A

Eukaryotes

Has true nucleus; bound by double membrane

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4
Q

Differences in strucutre between prokaryotes and eukaryotes

A

Eukaryotes

Cytoplasm filled with large complex collection of organelles

Mitochondria with cristae are “energy centres”

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

Prokaryotes

  • No membrane bound organelles independent of plasma membrane
  • Mesosomes are used in aerobic respiration
  • Transcription and translation occur simultaneously
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5
Q

Bacteria - structural components

A
  • Capsule
  • Pili (fimbriae) • Flagellae
  • Spores
  • Slime
  • Cell wall
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6
Q

Bacteria - capsule

A
  • Loose polysaccharide structure
  • Protectscellfrom phagocytosis
  • Protectscellfrom dessication
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7
Q

Bacteria - Pili/Fimbriae

A

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

  • Singular = fimbria (“thread”)
  • Not on all bacteria
  • May contain lectins which recognise oligosaccharide units on host cells
  • Facilitates bacterial attachment to host surfaces
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8
Q

Bacterial adherence to host cell

A
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9
Q

Bacteria - Flagellae

A

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

Singular = flagellum (“whip”)

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10
Q

Bacteria - spores

A

Metabolicallyinertform triggered by adverse environmental conditions

Adapted for long-term survival allowing regrowth under suitable conditions

Hard,multi-layered coats making spore difficult to kill

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11
Q

Common diseases caused by sporing bacteria

A
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12
Q

Bacteria - slime

A

Polysaccharide material

secreted by some bacteria growing in biofilms

Protects against immune attack

Protects against eradication by antibiotics

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13
Q

Cell walls - gram staining created by christian gram

G-/G+ differences

The four steps of Gram staining

A

• Differentiates bacterial species into 2 groups:

–Gram positive (+)

–Gram negative (-)

• Based on chemical and physical properties of the cell walls

Primary stain (crystal violet dye)

– Stains all the bacterial cells purple

Trapping agent (Gram’s iodine) (Mordent)

– Forms CVI complexes in the cell wall (larger than CV so not to be easily washed out of the PGN layer)

Decolourisation (alcohol / acetone)

– Interacts with lipids in cell wall

– Gram negative: loses outer LPS layer; exposes thin inner PGN layer; coloured complexes mainly wash away

– Gram positive: becomes dehydrated and traps the complexes in thicker PGN layer of cell wall

Counterstain (safranin)
– Gram negative: pink / reddish – Gram positive: purple

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14
Q

Cell wall components

A
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15
Q

Bacterial replication of genome

A

• 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 replication)

– 2 replication forks split off from origin and meet at bottom

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16
Q

What is the bacterial growth cycle?

What are the four stages of the bacterial growth cycle?

A
  • 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 = 2n

n = number of generations

1 - lag phase

  • Represents the period of active growth (ie. in size, not number)
  • Bacteria prepare for reproduction ie. Synthesising DNA and enzymes for cell division

2 - log/ exponential phase

• Cells divide at maximum rate

  • Uniform replication
  • Graph line is almost straight

3 - stationary phase

  • 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 population stabilises

4 - death phase

17
Q

Bacterial recombination

A

• Conjugation

– One bacterium connects itself to another through the pilus

– Genes are transferred from one bacterium to the other through this tube

• Transformation
– some bacteria are capable of taking up DNA from their

environment • Transduction

– involves the exchanging of bacterial DNA through bacteriophages.

18
Q

How to we identify bacteria?

A

• Bacteria are identified using a series of physical, immunological or molecular characteristics

– Gram stain: Gram positive / negative

– Cell shape: cocci; bacilli; helical / spiral

– Atmospheric preference: aerobic, anaerobic, microaerophilic

– Key enzymes – Fastidiousness

19
Q

What are some important bacteria?

A

Gram Stain

Gram pos - cocci - staphylococcus aureus

Gram negn - cocci - neisseria meningitidis

Gram neg - coccibaccili - haemophilus influenzae

Gram pos - bacilli - listeria monocytogenes

Gram neg - bacilli - escherichia coli

Gram neg - spiral - helicopter pylori

Cocci - spherical

Bacilli - rod- shaped

Spiral - helical rod

20
Q

Viruses

A
21
Q

Viral structural compnents

A

Nucleic acid

  • Double stranded or single stranded
  • Deoxyribonucleic acid or ribonucleic acid

ds dna, ss dna, ds rna, ss rna

Capsid

  • Protein coat / shell
  • Composed of protein subunits – capsomeres
  • Capsomeres consist of aggregated protomeres

• Various shapes of capsids – Rod-like – Polyhedral – Complex

Envelope

  • Amorphous structure surrounding some viruses
  • Composed of lipid, protein & carbohydrate

Spikes

• Glycoprotein projections arising from envelope

  • Highly antigenic
  • May have enzymatic, adsorption or haemagglutin activity
22
Q

Viral replication

A
  • 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

23
Q

Viral replication 6 steps

A

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 the host’scellular 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 the 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
24
Q

protozoa

A
25
Q

What is a common protozoal infection ?

A

Malaria and giardiasis and toxoplasmosis and cryptosporidiosis

26
Q

Fungi

A
27
Q

Common fungal infections?

A
28
Q

What is helminths?

A

Term used for all parasitic “worms”

3 main groups important in humans: – Cestoda: tapeworms
– Trematoda: flukes
– Nematoda: roundworms

Infections most common in tropical / sub- tropical climates

Usually intestinal species

29
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30
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31
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MD2001 Week 4 lectures (9 decks)

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