1.5 Origin of Cells

Pasteur’s experiments that spontaneous generation of cells and organisms

does not now occur on Earth

Pasteur’s experiment

Two broth in two different flasks with S shape necks, boiled, one neck is broken off

Results of pasteur experiment

The broth in experiment 1 turned cloudy while the broth in the 2nd one remained clear

Cell theory states

all living things are composed of cells, the cell is the smallest unit of life, cells only arise from pre-existing cells

Cells can only be formed by division of pre-existing cells

division, mitosis, meiosis

Examples of how cells only form from pre-existing cells

Cells are complex is the smallest unit, all known examples of growth be it of a tissue, an organism or a population are all a result of cell division, viruses are produced from simpler subunit, but they do no consist of cells, and they can only be produced inside the host cells that they have infected

Genetic code is universal of the

64 codons, produces the same amino acid in translation, regardless of the organism

logical deduction

all cells have arisen as the result of cell division from a single common ancestor

key problems

1. Non-living synthesis of simple organic molecules, sugars, and amino acids

2. Assembly of these organic molecules into polymers

3. Formation of polymers that can self-replicate

4. Formation of membranes to package the organic molecules

Reducing in the early days atmosphere

Hydrogen, nitrogen, water vapour, methane, ammonia, hydrogen sulfide

Miller & Urey 1953

Primeval soup full of monomers, trying to demonstrate chemical evolution

Conditions of miller and urey experiement

close galss vessel (stimulated atmosphere), they heated the water (stimulated volcanic activity) and sparked electricity through gases (simulated lightning)

Results of Miller and Urey experiments

12/20 naturally amino aicds found, 15% of the carbon was now in organic compounds

Miller and Urey recreated system

Low oxygen (reducting atmosphere), high radiation levels, high temp, electrical storms, water ….was boiled to from vapor, and mixed with methane, ammonia, and hydrogen, exposed to electrical charges for lightning

what was found

simple amino acids and complex oily hydrocarbons

Hydrolyse

miller and urey’s experiment allowed and prevented polymers forming

Deep-sea thermal vents

-Fissures in a planet’s surface from which geothermally heated water issues. Vents are commonly found near volcanically active areas

-Along with heat energy the vents issue a ready supply of reduced inorganic chemicals

-Vents provide the right conditions and chemicals to allow organic polymers to arise

formation of polymers that can self-replicate

• dna stable, effective at storing info but no rep with no enzymes

• rna can store info and self-rep

• in ribosomes rna is found in catalytic iste and plays a role in peptide bond formation

formation of membranes to package the organic molecules

found fatty acids→ phospholipid→ plasma membrane, isolated internal environment, optimal conditions for replicated or catalysis can be maintained

Endosymbiotic theory

explain existence of several organelles of eukaryotes, organelles originated as symbioses between separated single -celled organism

Nucelus formation

prokaryote grows in size and develops folds in its membrane to maintain an efficient SA: Vol, infoldings are pinched off forming internal membrane, nucleoid region is enclosed in the internal membrane and hence becomes the nucleus

Evidence supporting for mitochondria and chloroplast

own dna, 70s ribosomes, double membrane, same size as bacteria, transcribe own dna and use mRNA to synthesize own proteins, can only be produced by division of preexisting mitochondria and cholorplast