L7 : Life in Extreme Heat Flashcards
Parts of the Earth thermosphere?
Geothermal activity commonly associated with tectonic plate boundaries
- Tectonic plate ridges, pressure, continuous heat circulation
Land: volcanic areas, geysers, deserts
Ocean: vents, volcanoes
What extremophiles live within the thermosphere?
Hyperthermophiles: >80*c
Thermophiles: 45-80 *c
What are features of environments with extreme heat?
- Environmental stability
- No light
- High temps
- Desiccation (lack of water)
- High pressure (particularly subterranean)
- Low o2
- High UV radiation
- High toxicity (eg. heavy metals)
- High salinity
What are challenges for organisms in extreme heat?
Mechanical stress: fluid membrane, high diffusion, loss of structural integrity
Thermal stress: impaired metabolism, misfolded/denatured proteins
Oxidative stress: heavy metal toxicity, metabolic byproducts (ROS), lipid oxidation, DNA/RNA damage
Osmotic stress: dehydration, high salt conc
Adaptations for organisms in extreme heat?
Physical: smaller size, flagella (bacteria/eukaryotes), archaella
Behavioural: thermotaxis, chemotaxis, symbiosis
Biochemical: stress response systems, cell structure changes
What are the cell membrane heat adaptations?
Adaptations to maintain membrane stability
- More membrane transporter channels (eg. Na+/K+): regulate osmotic balance
- More saturated phospholipids: tightly packed
- Longer fatty acid chains: increased VDWs and Tm
- More cyclised lipids (5C FAs): structurally rigid
- More glycolipids: increase membrane rigidity
- More HSPs and thermoprotectants
- More pigments: protection from UV
What are the cell membrane modifications in Archaea?
- Ether bonds between glycerol backbone and lipid chains: stronger
- Isoprenoid lipids instead of FAs: stronger
- Monolayer membranes: thinner, allow more exchange
- Extra glycolipids
How do cell membrane modifications in Archaea assist with stress response?
Lower phase transition temperature
Maintain membrane fluidity
Aid nutrient transport
What proteins and components are involved in the cell environment stress response?
- Extracellular polymeric substances (EPS) bind and retain H2O, protect from dehydration, form biofilms
- Ion pumps/transporters regulate cytoplasmic K+/Na+, salts
- Trehalose protect cell from osmosis stress and dehydration
- Ribosomes with rigid structure
- Polyols act as osmolytes, regulate solute levels/pressure
- Compartmentalisation of proteins and metabolites into clusters offers localised protection against stress
What are 5 problems against DNA in extreme heats?
- High radiation
- ROS production
- Depurination
- Deamination
- Supercoiling stress
What are DNA adaptations for extreme heat?
- Hypermethylation
- High GC content
- Histone-like proteins
- DNA Gyrase
- Increased K+ levels
- Use of polyamines
- Robust DNA repair
- Thermostable polymerase
- Small genome
How do proteins adapt against heat-structural damage?
Tightly packed hydrophobic core, H-bonds, short loops
How do proteins adapt against protein misfolding in extreme heat?
- Increased Arg, Pro, Glutamic acid (forms multiple H-bonds, salt bridges)
- Increased Tyr, Trp, Phe (hydrophobic/aromatic help protein folding)
- Reduced Gly (small compact, adds structural flexibility)
- Reduced Ser and Thr (OH- at high temp increases susceptibility to denaturation)
- Shorter surface loops
- More disulfide bonds
How do proteins adapt against denaturation and aggregation in extreme heat?
- More chaperones to mediate folding (eg. HSPs)
- More alpha helices in proteins
- More thermoprotectants (eg. trehalose forming protective hydration cover)
- More polyamines to reduce aggregation
How do proteins adapt against loss of enzyme activity?
- Increased thermal stability
- Allosteric modulators (eg. ATP, AMP, NAD, metal ions)
- PTMs (eg. phos, meth)
What is the purpose of modifying DNA and RNA nitrogenous bases?
- Stabilise nucleic acids
- Protect from heat denaturation
- Regulate gene expression
- Involved in DNA repair
How are DNA bases modified?
Methylation of adenine and cytosine
Note: A methylation not seen in mesophiles
How are RNA bases modified?
tRNA replacement of uridine with dihydrouridine (D) and/or pseudouridine
More stable, avoiding deamination
How are sugars modified?
2’-O-ribose methylation
Common in archaea
