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BIOC0034 > L11 : Life in High Toxicity > Flashcards

L11 : Life in High Toxicity Flashcards

(47 cards)

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1
Q

Name earth, space and anthropogenic sources of ionising radiation?

A

Earth:
- Radioactive decay of mantle/crust, minerals
- high altitude
Space:
- Solar radiation
- Cosmic radiation
Anthropogenic:
- Healthcare applications
- Nuclear power and waste, accidents

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2
Q

Explain why radioresistant lineages are unclear?

A

Scattered distribution of radioresistant species
- Ability lost gradually from lineages through natural selection/genetic drift
- Ability evolved independently through horizontal gene/convergent evolution

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3
Q

What is the link between radiation and origin or life?

A

Much higher background radiation when life emerged
Early life must have had considerable radiation resistance and used energy from ionising radiation

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4
Q

How does direct ionising radiation damage DNA in cells?

A
  • Mutations
  • Direct breaks
  • Loss of nitrogenous bases
  • Cell cycle arrest
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5
Q

How does direct ionising radiation damage proteins in cells?

A
  • Denaturation
  • Misfolding
  • Carbonylation
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6
Q

How does direct ionising radiation damage lipids in cells?

A
  • Oxidation
  • Membrane disruption
  • Ion leakage
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7
Q

How does indirect ionising radiation damage the cell?

A
  • Organelle damage
  • Mitochondrial dysfunction (ATP depletion)
  • Dehydration (H2O becomes ROS)
  • Inflammation (cytokines, chemokines released
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8
Q

What is the consequences of ionising radiation on cells?

A

Apoptis or necrosis

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9
Q

What are 3 examples of reactive oxygen species (ROS)?

A

Superoxide (O2-)
Hydrogen peroxide (H2O2)
Hydroxyl free radicals (OH-)

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10
Q

What are 6 DNA adaptations for high radiation?

A
  1. Robust DNA repair mechanisms
  2. Gene redundancy
  3. Formation of highly compact, stable genome
  4. Use of pigmentation
  5. DNA dimer prevention
  6. Robust cell cycle checkpoint
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11
Q

List proteins and components involved in the cellular stress response to high radiation?

A
  • EPS
  • Outer membrane / LPS
  • Aquaporin
  • Thick, modified membranes
  • High levels antioxidants
  • Osmolytes
  • Dark pigments
  • Mn(II) phosphate complexes
  • Hydrolases and ATP dependent proteases
  • Chaperones (eg. HSPs)
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12
Q

How are membranes involved in stress response to high radiation?

A

Outer membrane/LPSs
- Extra barrier for protection
- Retain H2O

Aquaporins
- Allow H2O into cell, preventing dehydration

Thick membrane
- Modified lipids (unsaturated)

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13
Q

How are high antioxidants and dark pigments involved in stress response to high radiation?

A

High levels antioxidants
- Carotenoids, CAT, SOD
- Neutralise ROS

Dark pigments
- eg. melanin
- Absorb radiation
- Prevent oxidative damage
- Act as antioxidants

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14
Q

How are Mn(II) phosphate complexes involved in stress response to high radiation?

A

Unique to radiation resistant microbes
- Protect proteins
- Aid recovery from ROS damage

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15
Q

How are hydrolases, ATP-dependent protease involved in stress response to high radiation?

A

Degrade damaged DNA, proteins, organelles

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16
Q

Example of radioresistant archaea?

A

Euryarchaeota
(Hyperthermophilic - thermococcus gammatolerans)

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17
Q

Example of radioresistant bacteria?

A

Deinococcus
(Deinococcus radiodurans)

Bacteroidetes
(Hymenobacter xinjiangensis)

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18
Q

Example of radioresistant eukaryotes?

A

Fungi
(Cryptococcus neoformans, cladosporium)
Algae
(Hematococcus)
Tardigrades

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19
Q

Definition of radiation resistant organisms?

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A

Non-spore forming species that require ≥ 1 kilogray (kGy) ionising radiation to reduce population by 90% (D10 value)

20
Q

Where was Deinococcus radiodurans discovered?

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A

Isolated 1956 from radiation sterilised corned beef cans

No clear genetic affinity with any other bacterial lineage

21
Q

What are key features of Deinococcus radiodurans?

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A

Cells always exist in pairs or tetrads

Extraordinary ability to repair DNA

Thick cell envelope and 2 membranes separated by peptidoglycan layer

Tightly linked, ring-like nuclei with highly condensed genome

Produces high amounts Mn

Can delay cell cycle

22
Q

What are 3 examples of Chernobyl fungi variety?

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A
  • Cladosporium sphaerospermuum
  • Cryptococcus neoformans
  • Wangiella dermatidis
23
Q

What is a key feature of the Chernobyl fungi variety?

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A

High levels melanin
Absorbs radiation and turns into chemical energy (radiosynthesis)

24
Q

What is the NASA planetary protection program?

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A

Cross contamination concerns
Ensure Earth microbes do not travel along with space missions to planets that could be suitable for life

25
What are xenobiotics?
Substances that are foreign to an organisms normal chemistry
26
How can xenobiotics cause damage?
Dose dependent Heavy metals compete with normal components - Bind to and damage lipids, proteins, DNA
27
What are metalophiles?
Organisms that have an affinity for or thrive in the presence of xenobiotics and metals
28
Examples of toxic environments for metalophiles?
- Mining sites - Metal processing plants - Industrial sewage - Earth crust - Hydrothermal vent systems - Volcanic areas - Healthcare and cosmetics
29
What are the benefits of cell membrane adaptations to high toxicity?
- Increased permeability - Maintain osmotic gradient - Expel heavy metals
30
What are cell membrane adaptations to high toxicity?
- More unsaturated phospholipids - increase permeability - FAs with either bonds and isopropenoid chains (archaea) aid nutrient transport - More phosphate lipid head groups - bind +ve HM ions - More free -COOH groups - bind +ve HM ions
31
Explain adaptations for pumps and channels in membranes to high toxicity?
- Metal specific ion channels (eg. ArsB/C to remove toxic arsenic) - Non specific ion channels (porins, voltage, pH etc.) - Efflux pumps (eg. ABC transporters) - Proton pumps - power transporters
32
What are the benefits of cell environment stress responses in high toxicity?
- Remove excess metals - Neutralise toxicity - Prevent cellular damage
33
List cell environment stress responses to high toxicity?
1. Extracellular sequestration/ chelation 2. Precipitation/ mineralisation 3. Antioxidant production (eg. Glutathione, SOD) 4. Intracellular chelation (citrate, histidine) 5. Metal redistribution through compartmentalisation - minimise HM interference 6. Chaperones (HSPs) - regulate adaptation to HM stress 7. Sequestration with proteins 8. Vacuolar sequestration
34
Explain how sequestration is involved in environment stress response?
Extracellular sequestration - eg. in periplasm Sequestration with eg. metallothioneins or phytochelatins - small metal binding proteins Vacuolar sequestration - particularly eukaryotes - act as storage sites for excess metals
35
Explain how precipitation/ mineralisation is involved in environment stress response?
Trasform HMs into solid forms - Less reactive - Neutralised toxicity
36
What are adaptations against protein misfolding in high toxicity?
1. Cys and His - strong affinity for HMs 2. Asp and Glu acid - COOH bind +ve metal ions 3. Zinc finger motifs - stabilised by Zn+, allow cellular interaction under metal stress conditions 4. Alpha helices to tolerate mild unfolding 5. Chaperones (HSPs) to mediate folding 6. Cysteine - contain thiol (-SH) that binds HMs 7. Helix-turn-helix motifs - sense and bind HMs
37
What are adaptations against protein denaturation and aggregation in high toxicity?
1. Salt bridges 2. Metal cofactors (eg. Rubredoxins bind Fe+)
38
What are adaptations against loss of enzyme activity in high toxicity?
1. Enzyme redundancy - compensation 2. Evolution of specific binding motifs for metal ions
39
What are DNA adaptations against high toxicity?
Must withstand oxidative stress from high HM presence 1. Robust DNA repair mechanisms 2. Metal resistance gene expression 3. Dps (DNA protection during starvation) proteins - bind and shield DNA
40
List energy utilisation adaptations in high toxicity?
1. Dissimilatory metal reduction (DMR) 2. Assimilation 3. Metabolism adjustment - prioritise ATP production for active transport 4. Use alternative energy pathways (glycolysis even in presence of o2) 5. Enhanced redox recycling of HMs - to convert into useable energy 6. Use anaerobic pathways to cope with o2 lack 7. Phosphatase hydrolysis 8. Some use symbiotic relationships
41
What is assimilation?
Uptake and integration of HMs into cellular components for metabolic use eg. as cofactors
42
Why use phosphatase hydrolysis
Releases phosphates and energy Can be used for metal sequestration, chelation, transformation
43
What is dissimilatory metal reduction (DMR)?
Use HMs as terminal electron acceptors in respiratory chain
44
Examples of archaea with resistance to heavy metals?
Sulfolobus acidocaldarius - sulfur-rich geothermal springs Ferroplasma acidarmanus - acidic mine drainage
45
Examples of bacteria with resistance to heavy metals?
Cupriavidus metallidurans - metal-contaminated soils and mines Acidithiobacillus ferrooxidans - thrives in high Fe2+ and sulfur (mines)
46
Examples of eukaryotes with resistance to heavy metals?
Fungi (Aspergillus niger) - contaminated soils Common sunflower (Helianthus annuus) - metal contaminated soils
47
2 examples of Earths toxic environments as astrobiological models
Mercury - Most metal rich planet in solar system - 85% is core made up of Fe and Ni Io (Jupiters moon) - Core predominantly SiO2 rock and Fe - Sulfur rich volcanic surface - Extreme radiation from Jupiters powerful magnetic field

BIOC0034 (15 decks)

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