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
2
Q
Size
A
The importance of being small:
- Nutrient exchange and growth rate
- Rapid evolution due to a high selection rate of mutations
3
Q
Colour: Bacteria produce pigments
A
- Prodigiosin
- Staphyloxanthin
- Violacein
- Pyocyanin
4
Q
Prodigiosin
A
- Red colour
- Immunosuppressant
5
Q
Staphyloxanthin
A
- Golden colour
- Antioxidant
- Detoxify ROS
6
Q
Violacein
A
- Purple colour
- Antioxidant
- detoxify ROS
7
Q
Pyocyanin
A
- Blue colour
- Cytotoxicity
- Neutrophil Apoptosis
- Ciliary Dysmotility
- Proinflammatory
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
9
Q
Decarboxylation of Amino Acids to Produce Polyamines
A
- Putrescine, spermidine, cadaverine, etc.
- Role in bacterial physiology (ROS scavenger, signalling)
10
Q
The Gram Stain
A
- Stain; crystal violet
- Fix; iodine “mordant”
- Wash; alcohol
- Counter stain; safranin
11
Q
Gram-positive
A
- NO outer membrane
- Thick cell wall
12
Q
Gram-negative
A
- Outer membrane
- Thin cell wall
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
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
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
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
Gene Expression (Transcription)
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
Rho-independent Termination
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
Rho-dependent Termination
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
A Few Differences Between Transcription in Eukaryotes
- 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
A Few Differences Between Translation in Eukaryotes
- 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
Metabolism
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
Photo-
Use sunlight as their energy source
32
Chemo-
Use preformed molecules as their energy source
33
Organo-
Oxidise organic molecules as their source of electrons
34
Litho-
Oxidise inorganic molecules as their source of electrons
35
Heterotrophs
Use organic compounds as their source of carbon
36
Autotrophs
Use inorganic compounds as their source of carbon
