Experiments simulating primitive Earth conditions can make small organic molecules. Under special conditions, these molecules can make large stable proteins, ribonucleic acids (RNA), and deoxyribonucleic acids (DNA) {origin of life}|. DNA has optimum mutation rate, crossing-over, hybridization, and long length and so can be replication templates.
early-Earth molecules
Experiments replicating early-Earth conditions make formaldehyde, formic acid, lactic acid, acetic acid, urea, sugars, and hydrogen cyanide. From nitrogen, methane, ammonia, water, and hydrogen-gas mixtures, lightning or ultraviolet light can produce amino acids. Metallic carbides and water can react to form acetylene. Formaldehyde can polymerize to make ribose and other sugars.
replication
Living things replicate, so life requires replicating molecules. Proteins cannot be templates, because most amino acids can have no hydrogen bonding. RNAs are easy to create. However, RNA is also easy to hydrolyze, so only short RNA regions can replicate. DNA does not hydrolyze, because deoxyribonucleotides have no oxygen atom and prevent hydrolysis. DNAs are harder to create but can be templates.
cell functions
After DNA formation, DNA regions able to make functional RNAs and proteins arose. To these exons, evolution added and subtracted introns. Archaebacteria have tRNA and rRNA introns. Cyanobacteria eubacteria have leucine-tRNA introns. Eukaryote RNAs typically have introns. Eukaryote DNA has different intron types, such as self-splicing introns. Currently, gene exons have 1000 to 7000 functional DNA regions.
cell functions: photosynthesis
Earth life needs photosynthesis, using metals, enzymes, carbon dioxide, and water.
chirality
Perhaps, chirality is necessary.
sexual reproduction
Earth life needs sexual reproduction, for more variation and more competition. Sexual reproduction began 2.2 x 10^9 years ago. Sexual intercourse began 2 x 10^8 years ago.
mutation
Different DNA types change at different rates. Mitochondrial DNA mutates ten times faster than nuclear DNA. Mitochondrial DNA mostly comes from mother, but some paternal genes can enter and recombine. DNA-change rates can be faster if codon changes do not change amino acids produced. DNA-change rate is slower for histones and other fundamental proteins. DNA-change rate is slower in humans than in other species.
gene duplication
With sexual reproduction, genes can duplicate by unequal crossing over at recombination. If genes duplicate, one copy can change while the other still provides original functions, thus allowing genetic drift.
complexity
DNA amount and gene number can increase for whole genome, tRNA, rRNA, mitochondrial DNA, and globin DNA, increasing organism complexity.
Biological Sciences>Biology>Life>Origin
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Date Modified: 2022.0224