1.5 The Origin of Cells Flashcards
What is abiogenesis?
The theory that living cells arose from non-living matter is known as abiogenesis
Over what 4 stages did abiogenesis occur? simple
- simple organic molecules
- complex polymers
- self-replicating polymers
- molecules packaged in membranes
- How were simple organic molecules formed in abiogenesis?
There was non-living synthesis of simple organic molecules (from primordial inorganic molecules)
- What role did the organic molecules have? abiogensis?
These simple organic molecules became assembled into more complex polymers
- What allowed the complex polymers to develop further? abiogenesis
Certain polymers formed the capacity to self-replicate (enabling inheritance)
- What created structures similar to cells? abiogenesis
These molecules became packaged into membranes with an internal chemistry different from their surroundings (protobionts)
What experiment helped to show the non-living synthesis of simple organic molecules?
The non-living synthesis of simple organic molecules has been demonstrated by the Miller-Urey experiment
What was recreated in the M_U experiment?
Stanley Miller and Harold Urey recreated the postulated conditions of pre-biotic Earth using a closed system of flasks and tubes
What 3 conditions needed to be replicated? M-U
- high temperatures
- reducing atmosphere
- electrical discharge
How were high temperatures created? m-u
Water was boiled to vapour to reflect the high temperatures common to Earth’s original conditions
How was a reducing atmosphere created? m-u
The vapour was mixed with a variety of gases (including H2, CH4, NH3) to create a reducing atmosphere (no oxygen)
How was the electrical discharge created?
This mixture was then exposed to an electrical discharge (simulating the effects of lightning as an energy source for reactions)
What was done to the final mixture? m-u
The mixture was then allowed to cool (concentrating components) and left for a period of ~1 week
What were the results? m-u
After this time, the condensed mixture was analysed and found to contain traces of simple organic molecules
What was needed for the initial formation of biological life?
The chemical processes that contributed to the initial formation of biological life required specific conditions to proceed
This included a reducing atmosphere and high temperatures (>100ºC) or electrical discharges to catalyse chemical reactions
Why can living cells not arise independently by abiogenesis?
These conditions do not commonly exist on modern Earth and hence living cells cannot arise independently by abiogenesis
How are cells formed in today’s conditions?
Instead, cells can only be formed by the division of pre-existing cells (biogenesis)
What is biogensis?
Biogenesis describes the principle that living things only arise from other living things by reproduction (not spontaneous generation)
Who created the law of biogenesis?
The law of biogenesis is largely attributed to Louis Pasteur
What did louis pasteur’s experiment show?
demonstrated that emergent bacterial growth in nutrient broths was due to contamination by pre-existing cells
- What was the set up of his experiment? lp
Broths were stored in vessels that contained long tubings (swan neck ducts) that did not allow external dust particles to pass
- what did he do the broths first and why? lp
The broths were boiled to kill any micro-organisms present in the growth medium (sterilisation)
- In what broths were microorganisms present?
lp
Growth only occurred in the broth if the flask was broken open, exposing the contents to contaminants from the outside
- What was the conclusion from lp experiment?
From this it was concluded that emergent bacterial growth came from external contaminants and did not spontaneously occur
What is an endosymbiont?
An endosymbiont is a cell which lives inside another cell with mutual benefit
How were eukaryotic cells formed?
Eukaryotic cells are believed to have evolved from early prokaryotes that were engulfed by phagocytosis
How did the engulfed prokaryotic cell survive?
The engulfed prokaryotic cell remained undigested as it contributed new functionality to the engulfing cell (e.g. photosynthesis)
Over generations, the engulfed cell lost some of its independent utility and became a supplemental organelle
What 2 organelles are thought to be a result of endosymbiosis?
Mitochondria and chloroplasts are both organelles suggested to have arisen via endosymbiosis
What are the 5 pieces of evidence that support the extracellular origins of these organelles?
Membranes (double membrane bound) Antibiotics (susceptibility) Division (mode of replication) DNA (presence and structural composition) Ribosomes (size)
How can membranes prove that certain organelles are endosymbionts?
some organelles have double membranes (outer membrane may be vesicular in origin)
How can antibiotics prove that certain organelles are endosymbionts?
Susceptible to antibiotics - indicates organelles may have bacterial origins
How can divison prove that certain organelles are endosymbionts?
Reproduction occurs via a fission-like process
How can DNA prove that certain organelles are endosymbionts?
has own DNA which is naked and circular like prokaryotic DNA structure
How can ribosomes prove that certain organelles are endosymbionts?
Have ribosomes which are 70s in size (identical to prokaryotic ribosomes)
