Astrobio Exam 2

Molecules Common to All Life

ATP, DNA, RNA, proteins with iron-sulfur clusters, DNA polymerase, ribosomes,

acetyl-CoA

Similar features between humans and methanogens metabolism

Use of electron transfers to form a proton gradient across a membrane that allows for the generation of ATP through ATP synthase

Methanogen electron source and electron sink

Source: H2

Sink: CO2

Bold Traveler

Bacterium found 2.8 k below earth’s surface whose genome was sequenced:

• Energy production pathway: Radioactive decay of uranium produces radioactive nuclei which then allow for the creation of H₂ via radiolysis. The electrons from H₂ are used to reduce sulfate/sulfite to H₂S/HS^-, creating a pH gradient.

Sources of earth’s heat

• Radioactive decay of uranium (from stars and supernovas)

• Tidal friction (gravity from nearby celestial objects creates tidal bulges in earth’s ocean and crust) Tidal force proportional to 1/R³

Mars vs Earth (day + year length, mass, solar energy, atmosphere)

• Day length: ~same

• Year length: ~2x

• Mass: 1/9x

• Solar Energy: .5x

• Atmosphere: 1/100x as dense, very low pressure, 95% CO₂, 3% N₂ → most lost to space due to low mass and no magnetic field

Purpose of a magnetic field

Solar wind is the stream of charged particles flowing through space from the sun → a magnetic field protects from solar wind and prevents DNA damage and atmospheric stripping

Mar’s climate and presence of liquid water

Climate: Dry, desert-like, cold, dust storms

Evidence of water: IR spectroscopy of mineral composition from Mars Reconnaissance Orbiter

• likely covered in water in the distant past

ALH84001

Meteorite from mars found in Antarctica. Had similar shapes to earth life in carbonate globules and magnetite particles but not strong enough evidence bc also found in inorganic material.

• Evidence of mars origin: Trapped gas composition and ³⁶Ar/³⁸Ar isotope ratio match that of mars atmosphere

Commonalities between all hydrogenases and acetyl CoA synthases

All have metal-sulfur clusters at their active sites (FeS, NiS, NiFeS)

Sources of methane on mars

geology (water reacts with olivine to produce serpentine and methane); ancient methane trapped in clathrates that gets released; methanogens.

Jupiter’s Moons

 (closest) Io, Europa, Ganymede, and Callisto (furthest)

(heaviest) Ganymede, Callisto, Io, and Europa (lightest)

Jupiter’s solar flux compared to earth

Jupiter is 5 AU away: F∝1/5² → 1/25 of earth’s solar energy

Tidal Heating:

Caused by the stretching and squeezing of its interior due to a gravitational pull, depends on distance of moon from planet and eccentricity of orbit.

Potential Metabolism on Europa:

Electron sources: CH₄, Fe²⁺, H₂

Electron sinks: CO₂, SO₄^2-

photosystem II vs photosystem I

Photosystem II:

• P680 absorbs energy (light) and enters an excited P680* state before losing an electron and become P680⁺. To regain the electron, water is split and P680⁺ becomes P680 again. Once 4 e^- have been extracted from 2H₂O, O₂ is released. These e^- flow to PSI through electron carriers, forming an H⁺ gradient.

Photosystem I:

• P700 undergoes the same excitation as P680 except its e^- is transferred to NADP⁺ to be used in the dark reactions. It regains e^- from Plastocyanin (Cu⁺)

Location of reactions photosynthesis

Photosystem I and II are located within the thylakoid membrane along with ATP synthase. When e^- are transferred, protons are pumped from the stroma to the lumen (inside of thylakoid). To make ATP protons flow from the lumen into the stroma through ATP synthase.

Wavelengths of Light

Visible: 400-700 nm

UV: 100-400 nm

IR: 780 nm - 1 mm