2.1. Life, LUCA, microscopy Flashcards
When were the Sun and Earth formed (prebiotic period)/when was the first life formed?
Sun and Earth were formed 4.5 billion years ago. The pre-biotic period in the Earth’s development did not end for another 0.5 billion years and after that first life formed.
What are the possible spots for life formation?
The possible spots for accumulation of complex C-compounds and life formation are hot springs (terrestrial) and hydrothermal vents (ocean).
Compare conditions in prebiotic period and after life was formed.
Conditions: O2 levels, CO2 and CH4 levels, UV radiation, Temperatures, Natural disasters
Pre-biotic period: Low, High, High (no ozone layer), High (because of the greenhouse gases), Intense meteorite bombardment and frequent storms with lighting (providing E for chem reactions)
After 1st organism: Increased, Decreased, Decreased, Decreased
What are the exceptions to the general definition of life?
1| Mature erythrocytes (no nucleus, no DNA)
2| Aseptate fungal hyphae (continuous rows of fused cells)
3| Mule (sterile, reproduction impossible)
What are the steps in the formation of the first step and how was each replicated in a lab?
1| Inorganic into simple organic compounds – Miller-Urey experiment - result: after a few weeks, all a-a, nucleotides, monosaccharides, and ATP in a primordial soup.
2| Simple organic compounds (monomers) into polymers – Dropping the mixture of monomers on hot clay, rocks, sand -> polymers.
3| Plasma membrane surrounds cell content – Spontaneous formation of vesicles by coalescence of phospholipid molecules in primordial soup -> likely how membranes were made.
4| Self-replicating molecules - basis of inheritance – RNA is the presumed first genetic material because it is capable of both storing genes and self-replication without enzymes (unlike DNA) – some types of RNA can act as catalysts
Evaluate benefits and weaknesses of RNA as a genetic material.
Benefits: capable of self-replication (no enzymes needed), high mutation rate
Weaknesses: unstable, low capacity for gene storage, high mutation rate
What is LUCA?
the most recent population from which all organisms on Earth share a common descent – all (eukaryotic) organisms are derived from a common source (sharing certain traits)
What is the evidence for the existence of LUCA?
1| The universality of genetic code
2| All life shares a common mechanism of transcription and translation
3| Certain genes are distributed across all organisms (e.g. instructions for DNA replication)
What are the approaches used to estimate the dates of the first cells and LUCA? Define each.
1| Biochemical evidence – chemicals produced by cellular processes that provide evidence of past or present life. (earliest evidence of life dates to 3.42 bya in the form of stromatolites (layers of sediment laid down by microbes, Australia))
2| Phylogenetic comparisons – comparing the genome of different species to develop a timeline for evolutionary divergence – the number of differences between the genomes of two species is proportional to the time since they diverged from a common ancestor. (original LUCA genome established by searching for genes present in both prokaryotic domains (bacteria and archaea) - 355 genes are proposed to have originated directly from LUCA)
What is the molecular clock? Give an example of it.
- the estimated time of evolutionary divergence using genomic comparisons (the mutation grade of DNA/RNA/proteins) based on the assumption that there is a direct correlation between the number of sequence differences and the time since two species diverged
- if a gene mutates at 1 base pair per 100 000 years rate and 2 species have 6 differences in gene sequence, divergence occurred 600 000 years ago
When did LUCA’s evolution into archaea and bacteria happen? How was this discovered?
at any point between 2 to 4 billion years ago – based on phylogenetic comparisons and the molecular clock
What are white smokers?
alkaline hydrothermal vents (cracks on Earth’s surface with hot water and reduced chemicals (FeS)) that contain CH4, H2, NH3, and CO2, and have optimal conditions for the emergence of the protocell
Compare fossil and genomic evidence for the evolution of LUCA (concerning hydrothermal vents).
- fossilized evidence of bacteria discovered in hydrothermal vent precipitates dated at around 3.7 bya.
- genomic analysis supports the idea that the LUCA developed near hydrothermal vents – genes proposed to belong to LUCA are involved in the use of H2 as an E source.
What is magnification? How is it related to FOV? How is magnification calculated?
Magnification is the number of times an object is magnified (how much smaller/larger is the image than the real specimen). As magnification increases, FOV decreases.
Magnification = (image size)/(actual size)
What is resolution (what does it depend on)? Illustrate it with the example of EM.
Resolution is the ability of a microscope to show two close objects separately. It depends on the wavelength of the rays that pass through the spectrum (e- have a much shorter wavelength so EM has much a higher resolution).
