1.5 - The Origin of Cells Flashcards
Pasteurs experiment.
Louis Pasteur designed an experiment to test if sterilized nutrient broth could spontaneously generate microbial life.
- He placed nutrient broth into two swank necked flasks with an S-shaped end.
- He heated up each of the broths to kill existing microbes.
- He then broke off the neck of flask one, exposing it to the microbes in the air.
- After a while the first flask turned white and misty, while the second flask remained clear.
- This indicates that microbe growth only occurred in experiment 1.
-For the growth of microbes to occur, a source of contamination is needed.
All cells arise from preexisting cells
- cells multiply through division
- mitosis generates genetically identical diploid daughter cells
- meiosis generate haploid gametes
What supports the idea that all cells arise from preexisting cells
- Cells are complex structures and no mechanism has been found for producing cells from simpler subunits
- all known growth, whether it be tissue, organism, or population, is a result of cell division.
- Viruses can be formed from simpler subunits, but they do not contain cells and need the infected hosts cells to replicate
- genetic code is universal, each of the 64 codons create the same amino acid translation regardless of the organism.
What challenges the idea that all cells arise from preexisting cells
- Non-living synthesis of simple organic molecules (sugars and amino acids)
- arrangements of organic molecules into polymers
- ability of polymers to self replicate (enabling inheritance)
- Formation of membranes to package organic molecules
Conditions of prebiotic earth
oxygen did not exist in the atmosphere until plants began photosynthesizing
- hydrogen, ammonia, methane, water vapour
- “primeval soup”
Describe miller and ureys experiment.
Miller and Urey recreated the conditions of prebiotic earth in 1953.
- They wanted to demonstrate chemical evolution: the formation of complex molecules from simpler stock in the primeval soup
- They mixed molecules from above in a closed gas vessel to stimulate atmosphere, heated up water to stimulate volcanic activity, and sent electrical activity to stimulate lightning.
- after about a week, they found 13 of the 20 amino acids
- around 15% of the carbon was now in organic molecules
Miller and Urey - all cells arise from preexisting cells
- They recreated the conditions of prebiotic earth in a closed environment
- they heated up water to form vapour
- the vapour was mixed with methane, hydrogen, and ammonia
- Electrical discharges were sent through the gas to stimulate lightning
- they let the gas cool, and found simple amino acids and complex hydrocarbons.
- under the conditions of prebiotic earth, organic molecules could be formed.
2- rearrangment of organic molecules into polymers
In millers and Ureys experiment, bonds kept hydrolysing so amino acids couldn’t become polymers
deep sea thermal vents:
- fissures in a planets surface that allow geothermally heated water to release
- generally found near volcanic activity
- allow for the continued supply of reduced inorganic chemicals
- provide the right conditions and chemicals for the formation of organic polymers
3 - the ability to self replicate (enabaling inheritance)
- Dna, although good at storing information, can not self-replicate and needs enzymes to replicate.
- Rna can self replicate and store information - it can catalyze the formation of copies of itself
- in ribosomes rna is found in the catalytic site and plays a role in peptide bond formation
4 - formation of membranes to package the organic molecules
- phospholipids rearrange into a bilayer, creating an isolated internal environment.
- Optimal conditions like catalysis can be maintained
Endosymbiotic theory
Explains the origin of organelles. the theory states that organelles originated as symbioses of separate single-celled organelles
Formation of nucleus
- as prokaryotes grew, membrane folded over to maintain a viable surface area: volume ratio
- the membrane would pinch off into the cell forming an internal membrane
- nucleoid region is enclosed in the internal membrane to form the nucleus
Formation of mitochondria
- an aerobic proteobacterium would enter a larger anaerobic prokaryote
- it somehow survives digestion and becomes an endosymbiont
- it provides ATP for the prokaryote, allowing it to outcompete other prokaryotes and divide into more prokaryote with the endosymbiont
- aerobic proteobacterium evolves over time and is assimilates to become mitochondria
Evidence for endosymbiont theory for chloroplasts and mitochondria
- both contain DNA (naked and circular)
- both have ribosomes similar to prokaryotes (70s)
- both are a similar size to bacterium and are susceptible to antibiotics like chloramphenicol
- have a double membrane, and the inner membrane has proteins similar to prokaryotes
- both can transcribe DNA, mRNA can be used to synthesize proteins.
