lecture 5 -Archaea Flashcards
What are Archaea?
Archaea are one of the three branches of the tree of life.
• They are prokaryotic, unicellular organisms.
• They thrive in most of earth’s ecological niches, constituting 20%
of the biosphere.
What are methanogens?
archaeal organisms capable to convert carbon dioxide into methane
What is the structure of a ribosome?
Small subunit: 1 rRNA (1500 nucl.) + 20 proteins
Large subunit: 2 rRNA + 35 proteins
What is a molecular chronometer?
an indicator of how similar, how related different organisms are
Why is the small sub unit rRNA a very good molecular chronometer?
1) it’s universal, every prok. organism has this molecule;
2) it’s very conserved;
3) it’s very abundant in the cells.
Where do thermophilic archaea live?
They live in volcanoes, solfataras, hot springs, deep sea vents etc.
What are the strategies to survive at high temperature?
Cell membrane: it is made out of a single phospholipid layer that is resistant to the tendency for heat to pull apart a lipid bilayer normally found in bacteria and non-thermophilic archaea.
• Proteins: they are thermostable. 1) They tend to have highly hydrophobic cores, which increases internal ‘sticking’ and have more ‘salt bridges’ (ionic interactions between amino acids) on their surfaces. This helps the proteins to remain folded.
2) Thermophiles also produce special proteins called
chaperonins whose function is to refold partially denatured proteins.
• DNA: 1) reverse DNA gyrase and 2) DNA binding proteins
What are halophilic archaea and where do they live?
Halophilic = Halos (salt) + philic (loving)
They live in salt lakes, in the Dead sea and all hypersaline habitats (>1.5 M NaCl).
What are the strategies to survive in a hypersaline environment?
Water balance and compatible solutes:
1) pumping inorganic ions into the cell from the environment or
2) synthesizing an organic solute (generally sugars or alcohols). These compounds that adjust the water balance are called ‘compatible solutes’.
Halobacterium, one of the most studied halophiles, pumps large amounts of K+ inside the cell so that the concentration of K+ inside the cell is much greater than the concentration of Na+ outside the cell. This way the water flows inside the cell and there is a situation of positive water balance.
• Highly acidic proteins and low level of hydrophobic amino acids.
What are psychrophilic archaea and where do they live?
Psychrophilic = Psychro (cold) + philic (loving)
They live in Antarctica, icy seas, alpine and polar
environments at temperatures between 1 and 10°.
They can still metabolize at -40° and survive at
-45°.
How do psychrophilic archaea survive?
Cell membranes: contain unsaturated lipids at low temperature to maintain
membrane fluidity and function. ( the C=C double bond generates a kink in the membrane giving it this fluidity and flexibility)
• Proteins: they have a higher content of non-charged polar amino acids, in
particular glutamine (Gln) and threonine (Thr) and a lower content of hydrophobic
amino acids.
• Antifreeze proteins ?
What are methanogenic archaea and where do they live?
A large number of Euryarchaea produce methane (CH4).
They live in niches where there is no oxygen, so swamps, ocean, lake sediments and animal digestive tracts.
What do methanogenic archaea look like?
Some are cocci, some are irregular cocci, some are rods.
Which growth temperature do methanogenic archaea like?
Some are thermophiles and so grow at 80-90°, others grow at 50-60° or lower
temperatures.
