Lecture 2: origins of life Flashcards
(20 cards)
four undeniable facts:
- there is life on earth 2.all life on earth is essentially made of the same components 3.life on Earth is very complex. 4. all life on earth is related
LUCA
the first organism is referred to as the Last Universal Common Ancestor
How to organisms get the energy for life? 2 aspects to consider:
where they get the pieces: heterotrophs: obtain the molecules needed for nourishment from the environment, instead of synthesizing them directly. Autotrophs: organisms capable of synthesizing their own required molecules using an external energy source (sunlight, geothermal energy, etc).
Do they need oxygen to work: aerobic: organisms that use oxygen in their metabolic processes. Anaerobic: organisms that do not use oxygen in their metabolic processes
Earth 3.8 billion years ago:
had a very different environment, Remember it took about 1 billion years for life to start metabolizing and reproducing. CO2, H2O,CO, NH3, H2S, CH4. NO free O2. SO many sources of energy: lightning, volcano, radiation
Origins of life: origins of replication and metabolism:
abiogenesis: life from non life. the collection of organic molecules synthesized into macromolecules. macromolecules interacted with each other.
origins of life is historically elusive and inherently perplexing:
outdated idea of spontaneous generation: new species sprang into being spontaneously from non-living matter. bacteria from broth, mice from dirty clothes, maggots from meat. We can recognize these associations now as being great living environments for the above species. Series of experiments to explore where life comes from: Francesco Redi, Louis Pasteur and Jon Tyndall, Stanley Miller and Harold Urey, Alexander Oparin and JBS Haldane, Gunter Wachtershauser, Thomas Check and Sydney Altman
Disproving spontaneous generation:
1668 Redi disproved maggots spontaneously form on meat. Kept meat covered, away from flies compared to not covered. 1800s Pasteur and Tyndall disproved that microorganisms grow in sterile broth. sterilized broth and compared between exposed to air vs not exposed to air
Primordial soup hypothesis:
organic precursors formed near the earth’s surface. The scientists who inspired primordial soup hypothesis: 1920s two scientists, A.Oparin and J. Haldane. Suggested very little oxygen in young earths atmosphere, independently proposed that organic molecules such as simple sugars, amino acids, and nucleotide bases could form from basic raw materials. Prebiotics: organic compounds essential to life, before life. Chemical compounds persisted more readily than others, thus accumulated. making a ready supply of precursor organic molecules needed for life.
miller-urey experiment 1953:
stanley miller (a graduate student) and Harold Urey (his professor) designed an experiment that simulated the early earth’s environment. attempted to reproduce early atmosphere and produce organic compounds from hydrogen-rich atmosphere, liquid water, temp below 100c, simulated lightning by bombarding it with energy in the form of sparks. succeeded in producing larger carbon based compounds (macromolecules), later experiments produced more than 30 carbon containing compounds.
what did the miller-urey experiments demonstrate:
that biologically important molecules-amino acids, nucleic acid parts, sugars, etc- can be formed from non-living chemicals through natural processes. this scenario could work under various atmospheric mixtures. but no nucleotides!
issues with the primordial soup hypothesis:
inevitably very dilute. exposed/fragile, small ponds can be swept away in a hurricane for example.
primordial pizza/clay: iron-sulfur world hypothesis
prebiotics were further synthesized/developed on clay surfaces near hydrothermal vents (ridge smokers) of the sea floor. Gunter Wachterhauser 1990s. larger, highly complex, organized compounds formed, including RNA
the iron-sulfur hypothesis
thermal energy, concentrate components to facilitate reaction, iron and sulfur move electrons around easily- catalyzing organic reactions, beginning of autotrophic metabolism
Why is RNA significant:
consider this: DNA replication requires large complex protein enzymes. the instructions for building these enzymes are coded in DNA itself. Requires a lot of energy. RNA can catalyze chemical reactions, likely the first self-replicating informational molecule.
Ribozymes:
RNA molecule that catalyzes metabolic reaction. 1980s: Thomas Check and Sidney Altman discovered a cellular reaction that was catalyzed not by a protein but by a small RNA molecule. Ribozymes can: cut other RNAs, make new RNAs, Splice RNA fragments together (this kind of thing makes new genes!), attaching amino acids to growing proteins.
Vesicles are precursor to cells:
vesicle: simple hollow spheres composed of lipids and proteins. Form spontaneously, chemists have shown that if water containing proteins and lipids is agitated to simulate waves beating against ancient shores, the proteins and lipids combine to form hollow vesicles. Vesicles resemble living cells in several aspects. vesicles have a well-defined outer boundary that separates internal and external environments. organization, metabolism. growth, and replication
protocols are precursor to cells:
protocol: structurally similar to a cell but not alive. Ribozymes and other enclosed molecules would have been protected from degradation by the vesicle boundary. After sufficient growth, the vesicle may have divided, with a few copies of the ribozymes becoming incorporated into each daughter vesicle. The transition from protocol to living cell was a gradual process, with no sharp boundary between one state and the next
biology’s reigning hypothesis about the origins of life:
no definitive account of life’s origin can be tested definitively. the origin of life left no record. researchers exploring this mystery can proceed only by developing a hypothetical scenario and conducting further research. 4.3 billion years ago water was abundantly available on earth. 3.9 billion years ago life arose. that’s 400,000,000 years and a lot of failed almost cells.
life became more complex and diverse:
anaerobic bacteria: very simple. no further compartmentalization and specialization in the cells like eukaryotic cells that have formed organelles. need for synthesizing new macromolecules (requires energy!). some got REALLY good at this. specialized cell machinery for making usable energy. prokaryotic cells were precursors to mitochondria and chloroplasts. endocytosis: 1 cell engulfs something else by wrapping around it and pulling it in.
endosymbiosis:
1 cell engulfs another cell, and it forms a mutually beneficial relationship that stabilizes over time. larger cell benefits from enormous amount of energy produced from smaller cell- expand their metabolic repertoire. smaller cell gets stable, protected environment with influx of nutrients- starts replicating within the cell. mitochondria- present in all eukaryotic cells. chloroplasts- present in all plants, some weirdo protists. chloroplasts don’t replace mitochondria, they are in addition to mitochondira
