L4 & L5 : Molecular Adaptations for Survival Flashcards
How can extremophiles be categorised?
By specific conditions (eg. thermophile)
Extreme environments may pose combined challenges (eg. haloalkaliphiles)
Extremophiles adapt, defend, exploit
What are important functions of the cell membrane and associated challenges?
Barrier function to prevent unregulated in/outward transport
Improved impermeability to protons for acidophiles
Fluidity required for lateral movement of proteins
Fluidity of mesophilic membrane increased at high temps and decreased at low temp/high pressure
Modifications of cell surface proteins to support respiration in alkaliphiles
How do archaeal thermophiles decrease membrane fluidity?
Archaeal membranes have different kinds of phospholipids within them (ether-linked)
Isoprenoid ether lipids are liquid crystalline and provide low permeability from 1-100 deg
Tetraether-linked lipids increase rigidity and can span entire membrane
Nature of the chain is regulated over temperature changes and has lower permeability due to less space between phospholipids
How does piezophilic Colwellia increase membrane fluidity
Different membrane composition so more fluid to maintain function under high pressure
More polyunsaturated FAs in phospholipids
Express delta-9-acyl phospholipid desaturase
No cis to trans isoemrases
Metabolism adapted to create required fatty acids
How does S. acidocaldarius lower proton permeability?
Thermophilic acidophile
Liposomes prepared from lipid fractions of S. acid show distinctive low proton permeability at different temperatures
How do acidophiles maintain membrane potential?
Mesophile typically have ~-73 mV
Proton gradient used by secondary transporters etc
May degrade weak acid uncouplers to prevent disruption of pH balance
Actively pump in K+ to maintain positive intracellular environment against high external proton conc
How do alkaliphiles use proton gradients as source of energy?
Rely on proton-motive force for ATP synthesis
Use ATP synthase to import proteins and maintain neutral internal pH
- Mutations give adaptations that allow enhanced ability to bind H+ at high pH
- Modified so ATPase activity absent and cannot release H+ extracellularly
Create localised lowered extracellular pH
- Make and secrete acids produced through fermentation
- Produce acidic, negative components for cellular surface
Examples of protein adaptations in extremophiles?
Structures and general characteristics may be adapted to maintain structure
Eg. denser core and tighter packing in high pressure environment
Surface of proteins may be altered to cope with altered internal conditions
Different chaperones for different conditions
How are psychrophile enzymes adapted?
Low temps mean less energy available
More flexible active sites with decreased substrate affinity
Also results in decreased specificity for substrates
Examples of opportunities that can be exploited?
In acidic conditioons:
Fe2+ more stable and oxidises less quickly to Fe3+
Acidophiles able to use Fe2+ oxidation as energy source
At low temps:
O2 more soluble
Psychrophles increase expression of aerobic metabolism enzymes
Acyl desaturases can use O2 as substrate in desaturation of FAs (flexible membranes)
What is the risk of low temps and increased O2 solubility?
Increased ROS and oxidative stress
Decreased levels of oxidisable AAs in proteins
Deletion of ROS-producing pathways
Increased synthesis of glutathione synthetase and superoxide dismutase
How can extremophiles be studied through cultivation?
~1% of bacteria in samples are cultivatable
Can attempt to recreate conditions or grow extremotolerants
Microbes may require growth factors provided by others
Optimal conditions can still result in slow growth
Material needed for DNA/mRNA analysis
How can extremophiles be studied using bioinformatics?
Phyla can be classified on basis of 16S rRNA genes
High throughput sequencing allows bioinformatic analysis, predict gene function based on homology, infer metabolic pathways
Large proportion of genes may have no predicted function
Challenges of adapting to environments?
Evolution suited to particular habitat with limited variation
Acute changes require immediate response - may not be sustainable
Chronic changes may induce alternative responses - may not be suitable
Adaptation may therefor alter sensory strategies and resulting responses
Why is oxygen important?
Terminal electron acceptor of aerobic respiration
Complex IV (cytochrome oxidase) of ETC reduces oxygen
Examples of hypoxic environments?
At seas level: 21% O2, 0.03% CO2
Higher altitude = decreased pressure and lower concs
Underground = 7.2% O2, 6% CO2 (lower ratio)
Diving mammals = up to 2h, anaerobic (adaptations affected by anticipated length of dive)
Frozen lakes = decreased photosynthesis
Eutrophication depletes O2
What are some general responses to hypobaric hypoxia?
Reduce need for oxygen
- decrease metabolic rate and switch to anaerobic metabolism
Improve delivery of oxygen
- changes to cardiovascular and respiratory system
Modify oxygen-sensing machines
What does acute response entail?
Immediate
Largely though nervous system
What does chronic response entail?
Acclimatisation, mitigates issues caused by immediate response
Changes in gene expression, altering behaviour and number of cells
What does adaptation entail?
Improve survivability (including next gen)
Changes in allele frequency
- Spontaneous mutations/admixture
Strategies differ between populations
Examples of established high altitude human populations?
Tibetan plateau - largest, most studied
Andean - most recent, seem less well-adapted
Ethiopian highlands - longest, least studied
Studies typically compare genetics with local sea-level populations
How is respiratory rate controlled by ventilatory drive?
Typically controlled by CO2 levels and pH sensing
Central chemoreceptors in brain stem stimulate hyperventilation at low pH (acidosis)
Alkalosis depresses ventilation
Kidneys may also regulate pH through production of bicarbonate
What is the acute hypoxic ventilatory response?
Carotid bodies detect decreased O2 - signals to nervous system, leading to hyperventilation
Pulmonary SMCs detect decreased O2 - cause constriction of vessel for ventilation-perfusion matching
What does hypoxic ventilatory response lead to?
Decreased CO2 and respiratory alkalosis
Kidneys mitigate through increased production of bicarbonate ions
Acute response to hypobaric hypoxia disrupted by regulatory response to hypercapnia (central chemoreceptors send stronger signals)
