(iv.) origins of life

gen bio 01:119:115

abiogenesis

a- lack of, bio- “life”, genesis- “create” = “first life developed from nonliving organic molecules

getting life out of nothing

4 steps of abiogenesis

abiotic synthesis of monomers → formation of macromolecules → formation of protocols → appearance of self replication

abiotic synthesis

creation of organic molecules from inorganic components spontaneously

4 requirements of abiotic synthesis

low oxygen (oxygen is highly electronegative which causes bonds with low electronegative elements)

energy source: solar radiation, geothermal, hydrothermal, volcanism

chemical precursors: CO2, H2O, CO, H2, N2, (CHON)

lots of time!

abiotic factors

water, atmosphere, temperature, soil, sunlight, wind

oparin-haldane

(competing hypothesis of origin of life) surface/shallow water (prebiotic soup)

life formed near earth’s surface through spontaneous formation of monomers

ion sulfur: deep sea vents, hydrothermal vents in cracks of ocean floor

hot water, minerals released from cracks, iron acts as catalyst

formation of organic macromolecules

can form on clay or rock surfaces

metal ions catalyze polymerization

→ facilitated by metal ions (Zn2+, Fe2+)

experimentally: polypeptides, polynucleotides, vesicles

formation of protocells

vesicle: fluid filled compartment surrounded by lipid membrane

→ forms spontaneously from lipids in water

protocells: aggregate of abiotically produced organic macromolecules, especially a vesicle exhibit attributes of living cells

→ unique internal chemical environment: outside and inside cell

electrical potential across membrane

absorbs material from environment as the environment increases (osmotic swelling)

→ divide if sufficiently large (no mechanism of hereditary: reproduction and metabolism)

self replication

rna leading candidate molecule as it can both store genetic information and act as a catalyst (ribozyme) → leads to copying

central dogma

(in living cells) dna → rna → protein

dna: genetic information stored, blueprint for all

“RNA came before DNA”

peptide world hypothesis

first replicating systems used rna to store and copy genetic information

used ran as both hereditary and as enzymes

divide and replicate until they became a protocell

limited role for polypeptides, not capable of carrying genetic information (no DNA as it is incorporated later)

ribozymes

RNA molecule with enzymatic properties, catalyzed reactions

→ results in cell replication

cleave RNA, RNA polymerization

DNA

double stranded, more stable through RNA-DNA hybrid

prokaryotes

has no nucleus

anaerobic (does not require/need oxygen)

heterotrophic (obtained organic molecules from environment)

autotrophy

obtains energy from sunlight to make own organic molecules

releases S2, (sulfur) after obtaining food

cyanobacteria

prokaryotes that use oxygenic photosynthesis

released O2 → caused oxygen revolution (2.5bya) which caused aerobes to become primary life form

proof: banded de formation

aerobes

capable of aerobic respiration

higher ATP yield compared to anaerobes

eukaryotes

cells with nuclei and membrane bound organelles

originated through endosymbiosis

endosymbiosis

larger cells eat smaller cells, resulting with the smaller cells becoming incorporated as a part of bigger cells

key events in history of life

1.) abiotic synthesis (early earth’s condition)

2.) abiogenesis

monomers → polymers → protocols → self-replication

3.) (first living cells) heterotrophic anaerobic bacteria

4.) photosynthesis bacteria

5.) aerobic respiration bacteria

6.) endosynthesis leads to eukaryotic cell