Lecture 2 - Origins And Evolution of Life Flashcards
3.8 BYA
microbial life appeared
conditions when life originated
- no oxygen
- high temperature
unresolved questions about early life
- what was the temperature?
- what’s the role of methane in the atmosphere?
- what is the source of earth’s first cells
RNA world hypothesis (60s)
- proposes that there was a stage in the early evolution of life when living organisms only depended on RNA to store genetic information, and catalyze chemical reactions
- DNA is limited to genetic information
- proteins are difficult to replicate
- RNA is involved in ancient processes
- ribosomal proteins built on RNA core
- ribonucleotide is the precursor for deoxyribonucleotide
- ATP is a ribonucleotide
- DNA replication requires a DNA primer
ribozyme
- RNA enzyme that catalyzes a reaction
- RNA can fold into 3D structures
- more chemically reactive than DNA due to the extra hydroxyl group
- many roles in many biological processes in extant cells
ribosome
- RNA and protein complex
- area where protein synthesis occurs
ending of the RNA world
- not optimal for all functions
- life later evolved to use DNA and protein
- RNA is unstable compared to DNA
- RNA has poorer catalytic properties than proteins
reaction centres
- rocks and clays are rich in metal sulfides
- they become reaction centres when there is high accumulation
- metabolism without an organism occurs
replicase
RNA that catalyzes its own replication
ligase
protein enzyme that joins two molecules
RNA ligase activity
RNA may have exhibited RNA ligase activity due to a mutation
hydrothermal vents
- possible sites of prebiotic chemistry
- less hostile and more stable than RNA
- abundant supply of energy through hydrogen and hydrogen sulfide
- abiotic production of molectules
- compartmentalization
compartmentalization
- restrict flow of molecules
- sequesters energy
- both will drive reactions forward.
- facilitate evolution
protocell
- simple version of a cell
- fatty acid membrane encapsulating RNA ribozymes
- capable of growth, replication, and evolution
theories on the evolution of the first coding RNA
- dual functioning ribozyme
- ribozyme synthesized coding molecule
FUCA
first universal common ancestor
LUCA
last universal common ancestor
origin of the genetic code
- an ancestor after FUCA may have a different genetic code
- but the genetic code must have happened before LUCA since all major branches of extant life share the same genetic code, where chirality of amino acids is conserved
- the genetic code is essential for evolution of heritable traits over generations
evolution
change in allele frequencies in a set of organisms over time
evolution factors
- new alleles can rise through mutations or recombination
- changes in allele frequencies can happen due to selection or genetic drift
mutations
random changes in DNA sequence that accumulate in all DNA sequences over time
recombination
segments of DNA are broken and rejoined to create new combinations of genetic material
evolutionary processes that generate diversity
- DNA replication errors
- errors in proof-reading
- replication/repair errors in DNA damage
- mutations (substitutions, indels, and duplications)
- recombination (homologous or non-homologous)
base-pair substitutions
- also called single nucleotide polymorphisms (SNPs)
- a change in amino acid sequence will result in a change in phenotype
- transitions
- transversions
transitions
interchanges A to G (or vice versa) or C to T (or vice versa)
transversions
interchanges of a purine for a pyrimidine base
degeneracy
- most amino acids are specified by more than one codon
mutation rates
- larger genomes have lower per base pair error rates
indels
- insertions
- deletions
- can be frameshift mutations if the indel is not in multiples of 3
duplications
- abnormally copied one or more times
- may alter the function of the resulting protein
levels of mutation
- organism
- population
- selection plays an important role
organism level
mutation is a change in the nucleotide sequence of a genome without incorporation of genetic material from non-progenitor cells, as well as its transmission to descendant after replication of the genome
- in selection, a mutation must yield an organism that can replicate
population level
propagation (possibly fixation) of an event in a population
- in selection, along with genetic drift, determines the abundance of the mutation within a population
genetic drift
- random process
- causes gene frequencies to change over time
- in the absence of natural selection, results in evolution in a population
selection
- basis of fitness
- non-random difference in survival/reproduction of individuals based on their fitness
