1.5 ORIGIN OF CELLS Flashcards
Cell division and the origin of cells
Cells can only be formed by the division of pre existing cells
1st cell: zygote from the fusion of sperm and egg
Spontaneous generations and cell origin
S.G: formation of living organisms from non-living matter
Popular because cells/ microorganism had not yet been discovered
Reasons for universal acceptance of cell origin
Cells are highly complex structures and no natural mechanism has been suggested for producing cells from simpler subunits
No example is known to increase in the number of cells in a population, organisms or tissue without cell division
Viruses are produced form simpler sub units but they do not consists of cells, and they can only be produced inside the infected host cells
Spontaneous generation and Pasteur
Swan neck flask experiment
Samples of broth in flasks them melted the necks and bent it into a variety of shapes
Boiled broth to kill organisms and left one un boiled as control
Fungi/other orgs appeared in unboiled flask
Even after a long period of time there were no organisms in boiled flask
Snapped neck: orgs apparent/ decomposed broth
Tested other subs: milk/ urine = same results
Conclusion: no org appeared “spontaneously”
Similar features of mitochondria and chloroplast
Suggest that they evolved from independent prokaryotes
Own genes: on circular DNA M
Own 70S ribosomes
Transcribe DNA and use mRNA to syn some of their own proteins
Only produced by division of pre existing mitochondria: chloroplast
Endosymbiosis and eukaryotes
The origin of eukaryotic cells is explained by the endosymbiotic theory: explains evolution or eukaryotes
Endosymbiosis step 1
- Mitochondria were once free living prokaryotes organisms that had developed the process of aerobic respiration
Endosymbiosis step 2
Larger prokaryotes that could only repairs anaerobically took the mitochondria in by endocytosis
Endosymbiosis step 3
Instead of killing/ digesting the smaller pro they lived in the cytoplasm of the larger one
Endosymbiosis step 4
As long as the small pro grew and divided as fast as the larger pro they could persist indefinitely inside larger cells
Endosymbiosis/ mutualistic relationship of smaller and larger prokaryotes
Larger cells provided smaller cells with food
Smaller cells provided larger cells wij efficient E: aerobic respiration
Natural selection favoured cells that had this developed this type of relationship
Endosymbiosis and photosynthesis
Origin of chloroplasts: if a prokaryote had developed photosynthesis and was taken in by a larger prokaryote it could
have developed the chloroplast of a photosynthetic eukaryote
Origin of the first cells
The first cells must have arisen from non-living matter
Complex structures can’t arise by
evolution–> evidence that this CAN happen in a series of stages of a long period of time
Origin of first cells step 1
Producing carbon compounds such as sugar and amino acids: miller and Urey
Steam passes through as mixture of CH4/H+/NH3+ = early earth atmosphere
Electric discharges= lightning
Produced AA and other subs needed for life
Origin of the first cells step 2
Assembly of carbon compounds into polymers
Deep sea vents
Chemical represents supplies of E for the assembly of carbon compounds into polymers
