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PRIS > Bacteria Structure > Flashcards

Bacteria Structure Flashcards

1
Q

What types of cell are bacteria?

A
  • prokaryotic cells
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2
Q

What are prokaryotic cells?

A
  • cells have simple structure and lack a nucleus an membrane- bound organelles i.e., specialized structures surrounded by a membrane
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3
Q

What type of organism are bacteria and what is their size?

A
  • unicellular organisms
  • variable length (0.1-5 um)
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4
Q

Bacterial morphology - what are the two main shapes?

A
  • cocci (round-shaped)
  • bacilli (rod-shaped)
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5
Q

What causes the different bacteria shapes?

A
  • the cell wall
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6
Q

What components may up a bacterial cell?

A
  • granules
  • capsule
  • cell wall
  • cytoplasmic membrane
  • flagella
  • single coiled circular chromosome
  • fimbriae
  • cytoplasm
  • ribosomes
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7
Q

What is the cytoplasm?

A
  • jelly-like aqueous solution (80% water)
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8
Q

What does the cytoplasm contain?

A
  • one nucleoid
  • one or several plasmids
  • many ribosomes
  • granules
  • various types of solutes
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9
Q

What is a nucleoid?

A
  • The bacterial chromosome is one large circular molecule that is largely composed of DNA (60%) with small amounts of RNA and proteins that regulate transcription (transcription factors) or carry out dynamic spatial organisation of the nucleic acid (nucleoid-associated proteins, NAPs)
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10
Q

What is a plasmid?

A
  • a large circular molecule of double stranded DNA that can replicate autonomously from the chromosome
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11
Q

What are granules?

A
  • concentrated deposits of various nutrients or wate such as starch or glycogen
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12
Q

What are the various types of solutes found in the cytoplasm?

A
  • macromolecules such as proteins (enzymes) and nucleic acids (DNA and RNA)
  • small molecules that are energy sources, precursors of macromolecules, metabolites or vitamins
  • inorganic ions required for enzymatic activity
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13
Q

What is the structure if the nucleoid?

A
  • 1000 times longer than a bacterial cell and extensively folded to form a dense body that can be visualised by electron microscopy
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14
Q

Proteins encoded by plasmid genes are not essential under normal conditions but are important in what?

A
  • important to cause disease (virulence factors) or to survive to antibiotics and heavy metals (resistance genes)
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15
Q

What are ribosomes the site if?

A
  • these organelles are the site of protein synthesis
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16
Q

How is ribosome size measured?

A
  • their size is measured by the Svendberg, which is a measure of sedimentation rate by centrifugation
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17
Q

What is the difference in ribosome size in eukaryotic cell and bacteria?

A
  • bacteria = 70S
  • eukaryotic cells = 80S
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18
Q

Ribosomes consist of two subunits what are they?

A
  • A small subunit (30S) that reads the mRNA
  • A large subunit (50S) that assembles amino acids into the peptide chain
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19
Q

What is the cytoplasmic membrane?

A
  • flexible structure composed of a phospholipid bilayer and proteins (e.g., membrane receptors, transport protein and enzymes)
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20
Q

What are the three main functions of the cytoplasmic membrane?

A
  • permeability barrier containing a variety of different transport systems that selectively mediate passage of substances into and out of the cell (selective permeability)
  • it plays a key role in bacterial respiration since adenosine 5’ - triphosphate (ATP) is synthesized using electron transport systems located on the membrane
  • anchor for external structures such as flagella and fimbriae
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21
Q

Describe the phospholipid bilayer:

A
  • Each phospholipid molecule has one head that ‘likes’ water (hydrophilic) and two tails that ‘hate’ water (hydrophobic)
  • The inner double layer of tails forms a barrier to most hydrophilic molecules
  • Only small molecules (H2O, O2 and CO2) and some lipid-soluble compounds can enter the bacterial cell by passive diffusion
22
Q

What is the cell wall or envelope?

A
  • ridged structure that protects the cell from osmotic lysis and provided mechanical protection
23
Q

What is the main component of the cell wall or envelop?

A
  • peptidoglycan, a polymer of alternating polysaccharide subunits (NAG and NAM) cross-linked by short chains of peptides
24
Q

What is the structure of gram positive cell wall?

A
  • gram-positive bacteria have a thick peptidoglycan layer and tectonic acids
25
Q

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

A
  • Gram-negative bacteria have a thin layer of peptidoglycan surrounded by an outer membrane, which is similar to the cytoplasmic membrane but the outer surface contains lipopolysaccharides (LPS) and open channels (porins) that allow diffusion of small hydrophilic molecules into the periplasmic space
26
Q

The LPS structure has 3 regions what are these?

A
  • An external polysaccharide chain (somatic O antigen used for serotyping)
  • A core oligosaccharide that contains unusual sugar residues (e.g., heptose)
  • An internal lipid region (lipid A) responsible for the toxicity if Gram-negative bacteria (endotoxin)
27
Q

What are two types of atypical bacteria?

A
  1. mycoplasma
  2. mycobacteria
28
Q

Mycoplasma do not have a cell wall which means what?

A
  • they cant be visualised by Gram stain and are resistant to antimicrobials targeting the cell wall such as penicillin
29
Q

What are mycobacteria?

A
  • Gram-positive bacteria with a wax-like outer membrane composed of mycolic acids that prevent uptake of the dyes used in the Gram stain.
    Their detection by microscopy requires another method
    (Ziehl-Neelsen staining) based on the
    use of carbol fuchsin, a dye that binds
    to lipids.
30
Q

What is a capsule or glycocalyx?

A
  • a polysaccharide layer outside of the cell wall, which confers mucoid appearance to bacterial colonies
31
Q

What do capsules mediate?

A
  • mediate attachment to particular surfaces that protect bacteria from phagocytosis by protozoa or white blood cells (phagocytes) and from antimicrobial agents
32
Q

Why are surface components important in bacterial ecology?

A
  • they mediate contact of the bacterial cell with the surrounding environment
33
Q

What are the three main types of surface components?

A
  • flagella
  • fimbriae
  • endospores
34
Q

What are flagella?

A
  • (3-20 um long, 0.01 um diameter) are filamentous protein structures that allow the bacterial cell to move/swim and have antigenic properties (H antigen of Salmonella)
35
Q

What are fimbriae?

A
  • (0.5 um long, 10 nm diameter) are shorter and stiffer than flagella and are usually involved in adherence to surfaces (virulence factors)
36
Q

Bacteria can have one or multiple flagella that can be arranged in 4
different ways - what are these?

A

-Monotrichous
- Lophotrichous
- Amphitrichous
- Peritrichous

37
Q

What is monotrichous?

A
  • bacteria have a single flagellum
38
Q

What is Lophotrichous?

A
  • bacteria have multiple flagella located at the same end on the bacterial surface
39
Q

What is Amphitrichous?

A
  • bacteria have a single flagellum on each of two opposite ends (only one flagellum operates at a time).
40
Q

What are peritrichous?

A
  • bacteria have flagella projecting in all directions
41
Q

Name 4 example of flagella in veterinary pathogens:

A
  1. Vibrio Cholera
  2. Pseudomonas
  3. salmonella
  4. campylobacter
42
Q

Some bacteria produce endospores - what are they?

A
  • dormant highly resistant
    bodies that ensure survival during adverse environmental conditions
    (heat, dessication and toxic chemicals)
43
Q

Spore structure - what does the core contain?

A
  • The core contains genomic DNA and is surrounded by the inner membrane and a ‘normal’ peptidoglycan layer (germ cell wall)
    followed by:
  • A thick but ‘looser’ peptidoglycan layer that confers resistance to heat and desiccation (cortex) surrounded by the outer membrane
  • A keratin-like protein coat that serves as a permeability barrier (coat)
  • The outermost layer (exosporium) has variable composition and is not present in all spore-forming bacteria
44
Q

What can be used for classification of endospore-forming species?

A
  • Shape, size and position within the mother cell
45
Q

What are the non-bulging classes of endospores?

A
  • oval central
  • spherical central
  • oval sub terminal
46
Q

What are the bulging classes of endospore?

A
  • oval sub terminal
  • oval terminal
  • spherical terminal
  • free spore (not bulging)
47
Q

What are the spore-forming bacteria of veterinary interest?

A
  • Bacillus
  • Clostridium
48
Q

What are examples of bacillus?

A
  • B anthracis
  • B larvae
49
Q

What are examples of clostridium?

A
  • C. perfringens and C. difficile
  • C. tetani
    -C. botulinum
50
Q

What is sporulation and germination?

A
  • The process leading to spore formation is called sporulation
  • the reverse process leading to the vegetative cycle is called germination
51
Q

How is sporulation triggered?

A
  • triggered by unfavourable conditions
52
Q

Germination occurs in response to what?

A
  • Germination occurs in response to specific factors such as heat,
    abrasion of the spore coat or environmental acidity

PRIS (16 decks)

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