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Microbiology > Cell Structure and Function in Bacteria > Flashcards

Cell Structure and Function in Bacteria Flashcards

1
Q

Morphology

A
  • Cocci; e.g. Staphylococcus aureus
  • Rods; e.g. Escherichia coli
  • Curved; Vibrio cholerae
  • Spiral; e.g. Titanospirillum velox and Borrelia burgdoferi
  • Exotic; e.g. Stella humosa and Aloquadratum walsbyi
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2
Q

Size

A

The importance of being small:

  • Nutrient exchange and growth rate
  • Rapid evolution due to a high selection rate of mutations
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3
Q

Colour: Bacteria produce pigments

A
  • Prodigiosin
  • Staphyloxanthin
  • Violacein
  • Pyocyanin
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4
Q

Prodigiosin

A
  • Red colour

- Immunosuppressant

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5
Q

Staphyloxanthin

A
  • Golden colour
  • Antioxidant
  • Detoxify ROS
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6
Q

Violacein

A
  • Purple colour
  • Antioxidant
  • detoxify ROS
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7
Q

Pyocyanin

A
  • Blue colour
  • Cytotoxicity
  • Neutrophil Apoptosis
  • Ciliary Dysmotility
  • Proinflammatory
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8
Q

Contribution to Human Odors

A

Degradation of apocrine secretion products

  • Conversion of leucine to isovaleric acid (short chain fatty acid)
  • Production of propionic acid (propanoic acid) by propionibacteria
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9
Q

Decarboxylation of Amino Acids to Produce Polyamines

A
  • Putrescine, spermidine, cadaverine, etc.

- Role in bacterial physiology (ROS scavenger, signalling)

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10
Q

The Gram Stain

A
  • Stain; crystal violet
  • Fix; iodine “mordant”
  • Wash; alcohol
  • Counter stain; safranin
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11
Q

Gram-positive

A
  • NO outer membrane

- Thick cell wall

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12
Q

Gram-negative

A
  • Outer membrane

- Thin cell wall

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13
Q

Capsules

A
  • Most are made of polysaccharides
  • Some are made of amino acids
  • Covalently bound to cell wall or outer membrane
  • Conver resistance to host phagocytes/bacteriophages
  • Keep environment hydrated
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14
Q

Exopolysaccharides

A
  • Homo- or heteropolysaccharides non-covalently attached to the cell surface
  • Important for biofilm formation
  • Some are economically important, e.g. xanthan gum
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15
Q

S-layers

A
  • Facultative structures; don’t exist in most model organisms
  • Non-covalently bound to the cell surface
  • Proteinaceous crystalline arrays; self assembly products
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16
Q

Outer Membrane (Gram -)

A
  • Phospholipids
  • Proteins including porins (trimeric assembly for solute transport)
  • Lipoproteins (Braun Lipoprotein/Lpos) covalently linked to peptidoglycan; others like ompA bind non-covalently
  • LPS (endotoxin): potent activator of the immune system (sceptic shock)
17
Q

Peptidoglycan

A
  • Glycan chains alternating N-acetylglucosamine (G) and N-acetylmuramic acid (M), substituted via short peptides (L- and D- amino acids)
  • Old school; Exoskeleton (protective role): acts as a sieve to regulate exchanges with surrounding environment
  • Real life?; elastic 3D network, subcellular compartment and dynamic regulation of exchanges with the environment
18
Q

Cytoplasmic Membrane

A
  • Phospholipids
  • Hopanoids (equivalent to sterols in eukaryotes)
  • Proteins (transporters, sensors, etc.)
19
Q

Role of Phospholipids in Membrane

A
  • Unsaturated fatty acids modulate membrane fluidity and permeability
20
Q

Role of Hopanoids in Membrane

A
  • Modulate membrane fluidity and permeability
21
Q

Role of Proteins in Membrane

A
  • Ion, proteins or nutrient transport
22
Q

Chromosome

A
  • Always made of dsDNA
  • Single circular chromosome in the vast majority of bacteria
  • Variable size: between 0.5-9.4 Mbp
  • The chromosome is organised as a nucleoid (histone-like proteins/supercoiling)
23
Q

Plasmids

A
  • Always dsDNA, usually circular
  • Variable copy number (1 to several hundreds)
  • Size between 2-600 kbp
  • Can be (self)-transferable (horizontal transfer)
  • Carry resistance genes
24
Q

Gene Structure

A
  • No introns
  • Operons: one promoter, several Open Reading Frames (“ORFs”)
  • Genes are relatively small as compared to eukaryotes
25
Q

Gene Expression (Transcription)

A

1) The RNA polymerase scans DNA forming a loose complex
2) The sigma factor binds to two specific sequences upstream of the start codon (“close complex”)
3) The DNA is unwound, allowing the formation of the “open complex”; transcription starts, the sigma factor is released

26
Q

Rho-independent Termination

A

1) Requires a palindromic GC-rich region upstream of an AT-rich sequence
2) Once the GC-rich region has been transcribed, it forms a hairpin structure that makes RNA pol fall apart; helped by AT-rich sequence (few H bonds)

27
Q

Rho-dependent Termination

A

1) Rho proteins recognise and bind 72 residues GC-rich
2) Thanks to its RNA-dependent ATPase activity, the downstream RNA wraps around itself; once it reaches the polymerase, Rho unwinds the RNA-DNA duplex and releases the RNA polymerase

28
Q

A Few Differences Between Transcription in Eukaryotes

A
  • Transcription site (nucleus vs. cytoplasm)
  • 1 RNA pol in prokaryotes, 3 in eukaryotes
  • Transient direct interaction RNA pol/TF
  • Termination involves AAUAAA seq (mRNA cleavage)
  • mRNA is modified in eukaryotes (cap, polyA, splicing)
29
Q

A Few Differences Between Translation in Eukaryotes

A
  • Ribosomes are different
  • 80S ribosomes bind mRNA efficiently in the absence of tRNA; 70S interact with mRNA more productively in the presence of tRNA
  • The 40S subunit is guided by the 5’ cap on mRNA; The 30S subunit recognises the Shine-Dalgarno sequence
  • Translation is coupled with transcription in prokaryotes
  • Eukaryotic translation is specifically inhibited by cycloheximide
30
Q

Metabolism

A

Bacteria need:

  • An energy source; e.g. sunlight or preformed molecules
  • A source of electrons; e.g. organic or inorganic
  • A carbon source; e.g. organic or inorganic
31
Q

Photo-

A

Use sunlight as their energy source

32
Q

Chemo-

A

Use preformed molecules as their energy source

33
Q

Organo-

A

Oxidise organic molecules as their source of electrons

34
Q

Litho-

A

Oxidise inorganic molecules as their source of electrons

35
Q

Heterotrophs

A

Use organic compounds as their source of carbon

36
Q

Autotrophs

A

Use inorganic compounds as their source of carbon

Microbiology (6 decks)

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