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PRIS (CLB) > Bacterial structure > Flashcards

Bacterial 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 that have a simple structure and lack a nucleus or membrane-bound organelles

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3
Q

Are bacteria multi or uni-cellular organisms?
How big are they?

A

Unicellular organisms
Variable length (0.1-5um)

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4
Q

What are the 2 main shapes of bacteria?

A
  • Cocci (round)
  • Bacilli (rod-shaped
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5
Q

What determines the shapes of bacteria?

A

The cell wall

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6
Q

What components make up a bacterial cell?

A
  • Granules
  • Cell wall
  • Capsule
  • Cytoplasmic membrane
  • Flagella
  • Single coiled 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 solute
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9
Q

What is a nucleoid?

A

The bacterial chromosome is one large circular molecule 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

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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 waste 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 of the nucleoid?

A

1000x longer than bacteria 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 of?

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 S is the ribosome in a eukaryotic cell vs bacterial cell?

A

Bacteria = 70S
Eukaryotic cell = 80S

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18
Q

Ribosomes consist of 2 subunits - what are they?

A

1) A small subunit (30S) that reads the mRNA
2) 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

1) Permeability barrier containing a variety of different transport systems that selectively mediate passage of substances into and out of the cell (selective permeability)
2) It plays a key role in bacterial respiration since ATP is synthesised using electron transport systems located on the membrane
3) 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 & CO2) and some lipid-soluble compiunds can enter the bacterial cell by passive diffusion.
22
Q

What is the cell wall or envelope?

A

Rigid structure that protects the cell from osmotic lysis and provides mechanical protection

23
Q

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

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 +ve bacteria (cell wall)

A

Thick peptidoglycan layer and tectonic acids

25
Q

What is the structure of gram -ve bacteria (cell wall)

A

Thin layer of peptidoglycan surrounded by an outer membrane. Outer surface contains lipopolysaccharides (LPS) and open channels (porins) that allow diffusion of small hydrophilic molecules into the periplasmic space.

26
Q

LPS structure has 3 regions - what are these?

A

1) An external polysaccharide chain
2) A core oligosaccharide that contains unusual sugar residues
3) An internal lipid region responsible for the toxicity of gram -ve bactera

27
Q

What are 2 types of atypical bacteria?

A

1) Mycoplasma
2) Mycobacteria

28
Q

Mycoplasma do not have a cell wall - which means what?

A

They cannot be visualised by gram stain and are resistant to antimicrobials targeting the cell wall such as penicillin

29
Q

What are mycobacteria?

A

Gram +ve bacteria with a wax-like outer membrane composed of mycolic acids that prevent uptake of the dyes used in the gram stain.

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 WBC (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 3 main types of surface components?

A

1) Flagella
2) Fimbriae
3) Endospores

34
Q

What are flagella?

A

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

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

1) Monotrichous
2) Lophotrichous
3) Amphitrichous
4) 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 of 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 examples of flagella-possessing 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 (e.g., heat, dessication and toxic chemicals)

43
Q

Spore structure - what does the core contain?

A

Core contains genomic DNA and is surrounded by the inner membrane and a ‘normal’ peptidoglycan layer (germ cell wall)

44
Q

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

A

Shape, size and position within 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. difficile
C. tetani

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 (CLB) (23 decks)

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