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PDA > 9 Prokaryotes inside and out > Flashcards

9 Prokaryotes inside and out Flashcards

1
Q

Classification - The Gram Stain

A

Allows you to determine the two major classes - Gram +ve or Gram -ve

  1. Heat with crystal violet
  2. Add iodine solution
  3. Decolourise with alcohol (Gram +ve stain purple)
  4. Stain with safranin (gram -ve stain red)
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2
Q

Key Features of a Prokaryote Cell

A
  • No membrane-bound nucleus
  • Single circular DNA genome
  • Plasmid DNA free in cytoplasm
  • Enzymes and ribosomes free in cytoplasm
  • No mitochondria, Golgi or ER
  • Rigid, complex cell wall with appendages
  • Survival by adaptation to environment
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3
Q

Streptococcus pneumoniae

A
  • Gram +ve
  • Encapsulated coccus
  • Causes respiratory infections
  • SEM x3750
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4
Q

Escherichia coli

A
  • Gram -ve
  • Flagella and fimbriae
  • Enteric, urinary and nosocomal infections
  • SEM x3515
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5
Q

Clostridium difficile

A
  • Gram +ve rods
  • Anaerobic
  • Forms part of normal gut microflora
  • Causes inflammation (colitis) and abdominal disease
  • SEM x1200
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6
Q

Escherichia coli 0157:H7

A
  • Gram -ve rods
  • Anaerobic
  • Causal agent of haemorragic disease due to toxin secretion
  • SEM x9335
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7
Q

Helicobacter pylori

A
  • Gram -ve spirals
  • Moves using flagella
  • Associated with chronic superficial gastritis
  • SEM x2200
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8
Q

Mycobacterium tuberculosis

A
  • Gram +ve rods
  • Moves using flagella
  • Able to reside inside tissues due to hydrophobic cell wall
  • SEM x3000
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9
Q

Staphylococcus aureus

A
  • Gram +ve cocci
  • MRSA
  • Causes a variety of infections and disease
  • SEM x13335
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10
Q

Prokaryote DNA - Nucleoid

A
  • Circular, supercoiled, double stranded
  • Associated with histone-like proteins
  • Generally only one chromosome
  • E.coli chromosome 4.6 x 106 base pairs
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11
Q

Prokaryote DNA - Plasmids

A
  • Small loops of extrachromosomal DNA
  • Not essential for survival a priori
  • May contain genes that are expressed in response to certain situations
  • May be used to transfer genes between cells, e.g. resistance to antibiotics
  • Can be incorporated into the chromosome
  • Single DNA strand transferred between cells by conjugation using ‘rolling circle’ replication

plasmids used to transfer one bacterium to another

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12
Q

Ribosomes and Translation

A
  • Free in cytoplasm, composed of two large subunits
  • Small 30S subunit binds to mRNA
  • Large 50S subunit binds, completes 70S ribosome
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13
Q

Plasma (Cytoplasmic) Membrane

A
  • Phospholipid bilayer, embedded proteins
  • Contains cytoplasm, regulates transport
  • Three types of active transport in bacteria:
  • PMF-driven transport
  • ABC transport (ATP-Binding Cassette) • Group translocation e.g. glucose 6-P
  • Site of assembly of cell wall components
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14
Q

Peptidoglycan

A
  • Highly cross-linked polymer composed of carbohydrates and amino acids
  • Differences between Gram +ve and Gram –ve bacteria
  • Rigid, prevents osmotic lysis
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15
Q

Gram +ve Peptidoglycan

A

Staphylococcus aureus

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16
Q

Gram –ve Peptidoglycan

A

Escherichia coli

17
Q

Gram +ve Cell Wall

18
Q

Gram -ve Cell Wall

19
Q

Periplasmic Space

A

only present in gram -ve bacteria

  • Aqueous gel-like region between two membranes of Gram –ve bacteria
  • Contains enzymes associated with nutrient acquisition and transport
  • Also contains defence enzymes used to resist antibiotics, e.g. b-lactamase
20
Q

Outer Membrane and Capsule

A
  • Porins allow passive diffusion of molecules into periplasmic space
  • Braun’s lipoprotein
  • Lipopolysaccharides
  • Proteinaceous capsule, slime layer
21
Q

Lipopolysaccharide LPS

A
  • Lipid A embedded in membrane
  • Core polysaccharide, contains KDO
  • Antigenic, varies between bacteria
  • Net negative charge over cell surface of Gram –ve bacteria
  • May allow Gram –ve bacteria to evade immune response
22
Q

Flagella, Fimbriae and Pili

A
  • Flagella used for motility
  • Fimbriae and pili used for cell adhesion
  • Sex Pili important for movement of DNA between cells by conjugation
  • Tremendous diversity
23
Q

Bacteria and Disease

A
  • Few bacteria cause disease in humans
  • Commensal versus pathogenic bacteria
  • To cause disease the organism must:
  • Encounter and gain access to host • Evade defence mechanisms
  • Colonise and maintain colony
  • Carriage and spread of infection
  • Asymptomatic vs disease
24
Q

Inhibition of cell wall synthesis:

A

Penicillins, cephalosporins, bacitracin, vancomycin

25
Q

Inhibition of protein synthesis:

A

Chloramphenicol, erythromycin, tetracyclines, streptomycin

26
Q

Inhibition of nucleic acid replication and transcription:

A

Quinolones, rifampin

27
Q

Inhibition of synthesis of essential metabolites:

A

Sulfanilamide, trimethoprim

28
Q

Injury to plasma membrane:

A

Polymyxin B

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