Unit 4 - Lec 14 Flashcards
when did LUCA appear?
4 bya
what is LUCA?
thermophilic
what are hyperthermophiles mostly?
mostly Archaea
what can bacteria also be?
hyperthermophilic
what is the superheated vent water?
sterile- no microogranisms
- no biochemical markers that signal life
who is the record holder for temp?
methanopyrus
what happens at 150C?
- ATP degrades
- life forms have to deal with heat liability of a molecule that is universally distributed in cells
how to maintain stabilitity of DNA/RNA and proteins at higher temps?
- thermostable proteins
- thermosomes
- chaperonins
- reverse DNA gyrase
- RNA modification
thermosome function?
- keeps other proteins properly folded and functional at high temps
- maintains DNA
what happens after heat shock treatment?
sufficient to enable cells to keep growing and dividing
thermostable proteins
- specific folding
- not specific amino acids
- alpha helical structure in thermostable proteins
- very hydrophobic core - can’t easily fold
- high ionic interactions on surface - can’t easily fold
chaperonins
heat shock proteins
- help refold partially denatured proteins
DNA/RNA involved thermostability
- increased K+
- reverse DNA gyrase
- reverse gyrase introduces positive supercoils into DNA
- pos supercoiling stabilizes DNA
- highly basic DNA-binding proteins
- heat resistant lipids
ribosomal RNAs
- structural and functional components of ribosome- cell’s protein synthesizing apparatus
- small ribosomal subunit in hyperthermophiles has 15% greater proportion of GC base pairs
what does higher GC content of ribosomal RNA confer?
greater thermal stability
GC content of genomic DNA of hyperthermophiles is often _____
low
hypothesis for hyperthermophilic archaea, h2, microbial evolution
- biological molecules, biochemical processes and first cells arose on Earth around hydrothermal springs and vents on sea floor
- phylogeny of modern thermophiles suggests that they may be closest remaining descendants of ancient cells
what does the oxidation of H2 link to?
reduction of Fe3+, S^0, NO3- and sometimes O2
what is commonly spread in hyperthermophiles and why?
use of H2
H2 was available and there was many suitable inorganic e acceptors in primordial enviro
- metabolism evolved in primitive organisms
where do chemolithotrophic organisms live?
hottest temp possible
- 110C
what is the least heat-tolerant of all bioenergetic processes?
photosynthesis
- no hyperthermophilic representatives
hydrogen-metabolizing bacteria
H2 is sole e donor
O2 is e acceptor
fix CO2
hydrogenase enzyme
microaerophilic
Ni2+ must be present
some fix N2
what do diverse aerobic bacteria use?
atmospheric H2 for growth and survival
H2 oxidation
- globally significant process
- regulates composition of atmosphere
- enhances soil biodiversity
- drives primary production in extreme enviro
atmospheric H2 oxidation
- uncharacterized members of Ni-Fe hydrogenase superfamily
what conditions are unsuitable for enzymes?
very low level H2 and O2
NiFe hydrogenase
membrane bound H2 oxidizing metalloenzymes
low affinity to H2
no support oxidation of atmospheric H2
O2 poisoning problem
what are high affinity lineage NiFe hydrogenases?
capable to transfer electrons derived from atmospheric H2 oxidation to ETC
what are newly discovered enzymes?
significantly higher affinity for H2 and are insensitive to inhibition by O2
Ginter et al.
determined cryo-electron microscopy structure of hydrogenase Huc from Mycobacterium smegmatis
Huc
- enzyme that oxidizes atmospheric H2
- O2 tolerant hydrogenase
- multiple metal clusters
- highly stable at room temp with melting temp 78.3C
- oxidize atmospheric H2 below levels of detection in chromatography
- gas channels provide entrance for H2 (road to active site)
was O2-tolerant hydrogenase from E.coli Hyd1 able to tolerate high O2 levels?
no
structural basis for energy extraction from H2
four-lead clover
associated with membrane vesicles via stalk-like protrusion
cellular membrane
activity mainly associated with soluble fraction
where are bottlenecks?
between active site and enzyme surface
- H2 enters active site
- O2 excluded by bottlenecks
- O2 not getting close to active site
what is the critical point in O2-insensitivity?
bottleneck after three gas tunnels that precedes active site
