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Cell Biology > Microbial Structure > Flashcards

Microbial Structure Flashcards

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1
Q

What are the six main structural components of bacteria?

A 
1- Capsule
2- Pili (fimbriae)
3- Flagellae
4- Spores
5- Slime
6- Cell wall
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2
Q

Describe the structure and function of the bacteria capsule.

A

1- Loose polysaccharide structure
2- Protects cell from phagocytosis
3- Protects cell from dessication

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3
Q

Describe the structure and function of the bacteria pili

A

1- Singular: pilus
2- Composed of oligomeric pilin proteins
3- Appendage used for bacterial conjugation
4- Forms tube/bridge to enable transfer of plasmids between bacteria
5- Highly antigenic
6- Plays role in attachment

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4
Q

Describe the structure and function of bacteria fimbriae.

A

1- Singular: fimbria
2- Not on all bacteria (usually on Gram-negative)
3- May contain lectins which recognise oligosaccharide units on host cells
4- Facilitate bacterial atachement to host surface

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5
Q

Describe the structure and function of bacteria flagellum.

A 
1- Singular: flagellum
2- Organs of locomotion (movement)
3- Can be single or multiple
4- Composed of flagellin protein
5- 20nm thick helical hollow tube
6- Driven by rotary engine at the anchor point on the inner cell membrane
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6
Q

What are four examples of bacteria that have flagellae?

A

1- Vibrio cholerae
2- Helicobacter pylori
3- Campylobacter jejuni
4- Escherichia coli

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7
Q

Describe the structure and function of spores.

A

1- Metabolically inert form
2- Triggered by adverse environmental conditions
3- Adapted for long-term survival, allowing regrowth under suitable conditions
4- Hard, multi-layered coats for protection which make the spore difficult to kill

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8
Q

What are common diseases caused by sporing bacteria and what bacteria is responsible for each?

A 
1- Botulism, Clostridium botulinum
2- Gas gangrene, Clostridium perfringens
3- Tetanus, Clostridium tetani
4- Food poisoning, Clostridium perfringens
5- Anthrax, Bacillus anthracis
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9
Q

Describe the structure and function of slime.

A

1- Polysaccharide material
2- Secreted by some bacteria growing in biofilms
3- Protects against immune attack
4- Protects against eradication by antibiotics

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10
Q

What are the two different types of bacteria and what are these two categories based on?

A

1- Gram positive
2- Gram negative
3- Differentiation is based on the chemical and physical properties of the cell walls

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11
Q

What is the structure of a gram-positive cell wall?

A

1- 2 layers
2- Thick peptidoglycan layer facing outside of cell
3- Cytoplasmic membrane facing inside
4- Lipoteichoic acids present in membrane

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12
Q

What is the structure of a gram-negative cell wall?

A

1- 3 layers
2- Outer and inner cytoplasmic membranes
3- Thin peptidoglycan layer in the iddle
4- Liposaccharides present in membrane

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13
Q

What are the four steps of gram staining?

A

1- Primary stain
2- Trapping agent
3- Decolourisation
4- Counterstain

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14
Q

What happens in the first step of gram staining?

A

1- Primary stain
2- Crystal violet dye
3- Stains all bacterial cells purple

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15
Q

What happens in the second step of gram staining?

A

1- Trapping agent
2- Gram’s iodine
3- Forms CVI complexes in the cell wall which are larger than CV so as not to be easily washed out of the PGN layer

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16
Q

What happens in the third step of gram staining?

A

1- Decolourisation
2- Alcohol or acetone
3- Interacts with lipids in cell wall
4- If gram-negative: loses outer LPS layer, exposes thin inner PGN layer, coloured complexes wash away
5- If gram-positive: becomes dehydrated and traps the complexes in the thick PGN layer of the cell

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17
Q

What happens in the fourth step of gram staining?

A

1- Counterstain
2- Safranin
3- If gram-negative: pink/reddish
4- If gram-positive: purple

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18
Q

What is peptigoglycan?

A

1- Also known as PGN, murein
2- Polymer of sugars and amino acids
3- Forms mesh-like layer outside plasma membrane
4- Sugar components are alternating residues of N-acetylglucosamine and N-acetylmuramic acid

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19
Q

What is lipoteichoic acid?

A

1- Also known as LTA
2- Complex of teichoic acid and lipids
3- Provides cell rigidity
4- Recognised by host immune cells

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20
Q

What are lipopolysaccharides?

A

1- Also known as LPS
2- Found in gram negative bacteria
3- Essential for the function of the outer membrane
4- Elicits potent immune and inflammatory host responses
5- Produces endotoxins

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21
Q

What are outer membrane proteins?

A

1- Also known as OMPs
2- Lipoproteins and porins
3- Not endotoxins but do contribute to virulence

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22
Q

What are the main characteristics of bacterial replication

A

1- Asexual, reproduce by binary fission
2- Genetic information is found in circular DNA, which is distributed equally between each daughter cell
3- DNA is a self-replicating model: it makes an exact copy of itself before cell division
4- Replication in circular DNA starts at origin and has bi-directional replication

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23
Q

What are the four phases of bacterial growth?

A

1- Lag
2- Log/expotential
3- Stationary
4- Death

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24
Q

What does the lag phase represent?

A

1- The period of active growth in size and not number

2- Bacteria prepare for reproduction by synthesising DNA and enzymes for cell division

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25
Q

What does the log/expotential phase represent?

A

1- Cells divide at maximum rate
2- Uniform replication
3- Graph line almost straight

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26
Q

What does the stationary phase represent?

A

1- Cessation of growth
2- Exhaustion of nutrients
3- Accumulation of inhibitory end products of metabolism or limited oxygen availability
4- Number of cells dying balances the number of new cells, population stabilises

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27
Q

What does the death phase represent?

A

1- Number of dying cells begins to exceed number of newly born cells
2- Number of viable cells declines

28
Q

What is bacterial conjugation?

A

The transfer of genetic material from one cell to another via direct contact or via a bridge-like connection

29
Q

What are the four steps of bacterial conjugation?

A

1- Donor cell attaches to recipient cell with its pilus, which draws the cells together
2- The cells contact one another
3- One strand of plasmid DNA transfers to the recipient
4- The recipient synthesises a complementary strand, and so does the donor cell, so that each cell has its own complete plasmid

30
Q

In what categories can bacteria be classified?

A

1- Gram stain: positive or negative
2- Cell shape: cocci, bacilli, helical or spiral
3- Atmospheric preference: aerobic, anaerobic, microaerophilic
4- Key enzymes
5- Fastidiousness

31
Q

What is the gram stain and shape of Staphylococcus aureus?

A

1- Gram positive

2- Cocci

32
Q

What is the gram stain and shape of Neisseria meningitidis?

A

1- Gram negative

2- Cocci

33
Q

What is the gram stain and shape of Haemophilus influenzae?

A

1- Gram negative

2- Coccobaccili

34
Q

What is the gram stain and shape of Listeria monocytogenes?

A

1- Gram positive

2- Bacilli

35
Q

What is the gram stain and shape of Escherichia choli?

A

1- Gram negative

2- Bacilli

36
Q

What is the gram stain and shape of Helicobacter pylori?

A

1- Gram negative

2- Spiral

37
Q

What are the structural components of viruses?

A

1- Nucleic acid
2- Capsid
3- Envelope
4- Spikes

38
Q

What are the types of genetic information that may be present in viruses?

A

1- ds DNA
2- ss DNA
3- RNA

39
Q

What is ds DNA?

A

Double stranded DNA

40
Q

What is ss DNA?

A

Single stranded DNA

41
Q

Describe the structure and function of the capsid.

A

1- Protein coat or shell
2- Composed of protein subunits calls capsomeres
3- Capsomeres consist of aggregated protomeres
4- Various shapes of capsids

42
Q

What are the three different shapes of capsids?

A

1- Rod-like
2- Polyhedral
3- Complex

43
Q

Describe the structure and function of a viral envelope.

A

1- Amorphous structure surrounding some viruses
2- Composed of lipid, protein and carbohydrate
3- Help protect from or avoid host immune system

44
Q

Describe the structure and function of viral spikes.

A

1- Glycoprotein projections arising from the envelope
2- Highly antigenic
3- May have enzymatic, adsorption, or haemagglutinin activity

45
Q

What kind of cells can viruses infect?

A

1- Animal cells
2- Plant cells
3- Bacterial cells

46
Q

What are the six steps of viral replication?

A 
1- Adsorption
2- Penetration
3- Replication
4- Assembly
5- Maturation
6- Release
47
Q

What happens during adsorption in viral replication?

A

1- Virus binds to host cell

2- Highly specific

48
Q

What happens during penetration in viral replication?

A

1- Virus injects its genome into the host cell

2- This occurs by fusion, binding then ingestion

49
Q

What happens during replication in viral replication?

A

1- Capsid is digested by proteolytic enzymes

2- Viral genome replicates using the host’s cellular machinery

50
Q

What happens during assembly in viral replication?

A

Viral components and enzymes are produced and begin to assemble

51
Q

What happens during maturation in viral replication?

A

Virus fully develops

52
Q

What happens during release in viral replication?

A

1- Occurs at site of nucleic acid replication
2- Viral enzymes break down bacterial cell wall
3- RNA viruses are released as they are produced
4- DNA viruses are expelled from the host cells in inclusion bodies as cells autolyse
5- Viruses migrate either to plasma membrane or nuclear membrane
6- Envelopes are formed around he nucleocapsids by ‘budding’ of cell membrane
7- Slow continuous release of mature viral particles
8- No inclusion bodies

53
Q

What are protozoa?

A

1- Single celled eukaryotes

2- Can be a foreign organism leading to infection or disease

54
Q

What are the four classifications of protozoa?

A

1- Sporozoa: intracellular parasites
2- Flagellates: possess tail-like structures for motility
3- Amoeba: use temporary cell-body projections (psedopods)
4- Ciliates: move by beating multiple hair-like structures (cilia)

55
Q

What are four examples of common protozoal infections?

A

1- Malaria; Plasmodium falciparum
2- Giardiasis; Giardia lamblia
3- Toxoplasmosis; Toxoplasma gondii
4- Cryptosporidiosis; Cryptosporidium parvum

56
Q

What are fungi?

A

1- Eukaryotic
2- Multinuceate or multicellular organisms]
3- Reproduce asexually by budding or binary fission
4- Thick carbohydrate walls containing chitin and glucans
5- Grow as thread-like filaments called hyphae
6- Part of normal microbiota as well as being pathogens
7- Fungal infections are called mycoses

57
Q

What do fungal cell walls contain?

A

1- Chitin

2- Glucans

58
Q

How do fungi reproduce?

A

Asexually
1- Budding
2- Binary fission

59
Q

What are fungal infections called?

A

Mycoses

60
Q

What are examples of common fungal infections?

A

1- Candidiasis: Candida albicans
2- Cryptococcosis: Cryptococcus neoformas
3- Aspergillosis: Aspergillus flavus
4- Ringworm: Tinea corporis

61
Q

What are helminths?

A

1- Term used for all parasitic ‘worms’
2- Cestoda, tematoda and nematoda
3- Infections most common in tropical/sub-tropical climates
4- Usually intestinal species

62
Q

Where are helminth infections most common?

A

Tropical or sub-tropical climates

63
Q

What are the three main groups of helminths?

A

1- Cestoda: tapeworms
2- Trematoda: flukes
3- Nematoda: roundworms

64
Q

What are the modes of transmission of helminths?

A

1- Intermediate host: e.g. accidental ingestion of larvae in tissue of another hose
2- Fecal-oral route: e.g. accidental ingestion of eggs or larvae originating from feces of infected host
3- Active skin penetration: e.g. larval stages invade through skin
4- Injection by blood-sucking insect: e.g. larval stages develop to infectivity in insect intermediate host

65
Q

What are common types of infections due to helminths?

A

1- Bilharzia: Schistosoma haematobium, Shistosoma mansoni, Shistosoma japonica
2- Trichiuriasis: Trichuris trichiuria
3- Tapeworm: Taenia solium

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