Lecture 20: Origin of Life: Hypothesis Flashcards
(8 cards)
why is life difficult to define, and what are some of these complexities?
because some things life does, like build complex, grow, replicate, metabolise, can also be done by non-living things
may have ethical or social implications, like what qualifies as life
how does the RNA world theory work?
short RNA sequences formed spontaneously on the early earth (nucleobases, sugars, and phosphate derived from meteorites; sugars and nucleobases also form via cyanide chemistry)
some RNA sequences are able to catalyse their own reproduction, like ribozymes, and so come to dominate the population
lipid belayer vesicle growth and division occurs spontaneously, and when coupled to RNA division also provide a protective container and higher activity, leading to protocells
RNAs start building proteins to perform metabolic functions
at some point DNA takes over heredity and protein takes over catalysis
what happened between replicating molecules emerging and the first cells?
short polymers of ribonucleotides can be synthesised abiotically in the lab
monomers polymerise (join together) to form larger molecules like RNA
RNA acted as both the genetic material and a catalyst for reactions
protocells form spontaneously in lab experiments from mixtures of organic molecules
what is the urey-miller experiment and how does it work?
simulated conditions of early earth to test the hypothesis that simple inorganic compounds could form the building blocks of life
created an environment with water vapour, methane, ammonia, and hydrogen, then applied electrical sparks to mimic lighting
resulted in the formation of amino acids
what building blocks of organic chemistry/life have been found in meteorites, and what would the potential significance of this for early life be?
amino acids and nucleobases have been found
suggest they could have been delivered to early earth, potentially contributing to the origin of life
provided a source of raw materials for the formation of more complex organic molecules, and eventually, first living organisms
what are two of the current unknowns in the origin of life?
the precise conditions and chemistry that led to the first self-replicating molecules
specific mechanisms by which these molecules became enclosed within membranes, leading to the formation of the first cells
what problem does the RNA world scenario solve?
ribozymes can create proteins (polymerise amino acids), so possible nucleic acids came first and ‘recruited’ protein chemistry later
solving chicken and egg problem
what is the RNA world theory?
in the prebiotic world, RNA molecules may have been fully capable of ribozyme-catalysed replication, known as the RNA world
