L4 & L5 : Molecular Adaptations for Survival Flashcards
(57 cards)
How can extremophiles be categorised?
By specific conditions (eg. thermophile)
Extreme environments may pose combined challenges (eg. haloalkaliphiles)
Extremophiles adapt, defend, exploit
As an example, what challenges do extremophiles face in deep sea vents?
High pressure
High temperature
Lack of light
What are important functions of the cell membrane in extremophiles?
- Barrier function to prevent unregulated in/outward transport
- Regulates proton transport and maintains gradients for energy production
- Ensure membrane fluidity for protein function
How does membrane fluidity change with temp and pressure?
Increases at high temps
Decreases at low temps or high pressure
Affects protein mobility and membrane function
How do extremophiles adapt the cell membrane?
Different membrane compositions to alter fluidity and stability
Maintain function under extreme conditions
How do archaeal thermophiles decrease membrane fluidity?
Isoprenoid ether lipids
- Liquid crystalline
- Provide low permeability from 1-100 deg
Tetraether-linked lipids
- Increase rigidity
- Can span entire membrane
- Less space between phospholipids
How does piezophilic Colwellia increase membrane fluidity
- More polyunsaturated FAs in phospholipids
- Express delta-9-acyl phospholipid desaturase to introduce douvle bonds
- No cis to trans isomerases
- Metabolism adapted to create required fatty acids
Why is proton impermeability important for acidophiles?
Preserves proton gradient
- Used for ATP synthesis
- Prevents cytoplasmic acidification
How does S. acidocaldarius lower proton permeability?
Thermophilic acidophile
Lipids form liposomes with low proton permeability across range of temperatures
How do acidophiles maintain membrane potential?
Mesophile typically have ~-73 mV
Degrade weak acid uncouplers
- Prevent disruption of pH balance
Actively pump in K+
- 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 protons and maintain neutral internal pH
- Mutations give adaptations that allow enhanced ability to bind H+ at high pH
How do alkaliphiles create localised lowered extracellular pH
- Make and secrete acids produced through fermentation
- Produce acidic, negative components for cellular surface
How are proteins structurally adapted in extremophiles?
- Denser core and tighter packing in high pressure environment
- Surface residues of proteins may be altered to cope with altered internal conditions
- Different chaperones required for different conditions to maintain stability under stress
How are psychrophile enzymes adapted?
- More flexible active sites
- Allows function despite low kinetic energy
- Also results in lowered substrate affinity and decreased specificity
Why is Fe2+ oxidation exploited by acidophiles but not in neutral pH?
At neutral, Fe2+ rapidly oxidises to Fe3+
- Unusable
Acidic conditions stabilise Fe2+
- Viable energy source
How do psychrophiles exploit increased oxygen solubility at low temps?
Upregulate aerobic metabolism enzymes
Use oxygen-dependent acyl desaturases to maintain membrane fluidity
Risks of lower temps and increased oxygen solubility? How do psychrophiles cope?
Increased ROS production
Decrease production of oxidisable residues
Deletion of ROS-producing pathways
Upregulate SOD and glutathione synthetase
Why are extremophiles hard to cultivate?
~1% of bacteria in samples are cultivatable
Many require:
- Complex growth conditions
- Specific symbiotic factors
- Often grow very slowly (eve in optimum)
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
What are challenges of adapting to environments?
Evolution suited to particular habitat with limited variation
Acute or chronic respone changes may not be suitable or sustainable
Why is oxygen important?
Terminal electron acceptor of aerobic respiration
Complex IV (cytochrome oxidase) of ETC reduces oxygen
What challenges do hypoxic environments pose to organisms?
Limited oxygen availability
Reduced aerobic respiration
Need for rapid or sustained physiological and molecular adjustments
How does oxygen concentration vary in different environments?
At sea level:
21% O2
0.03% CO2
Underground
7.2% O2
6% CO2 (lower ratio)
Higher altitude
= decreased pressure
= same proportions but lower concentrations
What are some general responses to cope with hypoxia?
- Reduce need for oxygen
- decrease metabolic rate
- switch to anaerobic metabolism - Improve delivery of oxygen
- changes to cardiovascular and respiratory system - Modify oxygen-sensing machines
