Lecture 2 - Origins And Evolution of Life

Question 1

3.8 BYA

Answer 1

microbial life appeared

Question 2

conditions when life originated

Answer 2

• no oxygen

- high temperature

Question 3

unresolved questions about early life

Answer 3

• what was the temperature?
• what’s the role of methane in the atmosphere?
• what is the source of earth’s first cells

Question 4

RNA world hypothesis (60s)

Answer 4

• 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

Question 5

ribozyme

Answer 5

• 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

Question 6

ribosome

Answer 6

• RNA and protein complex

- area where protein synthesis occurs

Question 7

ending of the RNA world

Answer 7

• 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

Question 8

reaction centres

Answer 8

• rocks and clays are rich in metal sulfides
• they become reaction centres when there is high accumulation
• metabolism without an organism occurs

Question 9

replicase

Answer 9

RNA that catalyzes its own replication

Question 10

ligase

Answer 10

protein enzyme that joins two molecules

Question 11

RNA ligase activity

Answer 11

RNA may have exhibited RNA ligase activity due to a mutation

Question 12

hydrothermal vents

Answer 12

• 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

Question 13

compartmentalization

Answer 13

• restrict flow of molecules
• sequesters energy
• both will drive reactions forward.
• facilitate evolution

Question 14

protocell

Answer 14

• simple version of a cell
• fatty acid membrane encapsulating RNA ribozymes
• capable of growth, replication, and evolution

Question 15

theories on the evolution of the first coding RNA

Answer 15

• dual functioning ribozyme

- ribozyme synthesized coding molecule

Question 16

FUCA

Answer 16

first universal common ancestor

Question 17

LUCA

Answer 17

last universal common ancestor

Question 18

origin of the genetic code

Answer 18

• 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

Question 19

evolution

Answer 19

change in allele frequencies in a set of organisms over time

Question 20

evolution factors

Answer 20

• new alleles can rise through mutations or recombination

- changes in allele frequencies can happen due to selection or genetic drift

Question 21

mutations

Answer 21

random changes in DNA sequence that accumulate in all DNA sequences over time

Question 22

recombination

Answer 22

segments of DNA are broken and rejoined to create new combinations of genetic material

Question 23

evolutionary processes that generate diversity

Answer 23

• DNA replication errors
• errors in proof-reading
• replication/repair errors in DNA damage
• mutations (substitutions, indels, and duplications)
• recombination (homologous or non-homologous)

Question 24

base-pair substitutions

Answer 24

• also called single nucleotide polymorphisms (SNPs)
• a change in amino acid sequence will result in a change in phenotype
• transitions
• transversions

Question 25

transitions

Answer 25

interchanges A to G (or vice versa) or C to T (or vice versa)

Question 26

transversions

Answer 26

interchanges of a purine for a pyrimidine base

Question 27

degeneracy

Answer 27

• most amino acids are specified by more than one codon

Question 28

mutation rates

Answer 28

• larger genomes have lower per base pair error rates

Question 29

indels

Answer 29

• insertions
• deletions
• can be frameshift mutations if the indel is not in multiples of 3

Question 30

duplications

Answer 30

• abnormally copied one or more times

- may alter the function of the resulting protein

Question 31

levels of mutation

Answer 31

• organism
• population
• selection plays an important role

Question 32

organism level

Answer 32

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

Question 33

population level

Answer 33

propagation (possibly fixation) of an event in a population

• in selection, along with genetic drift, determines the abundance of the mutation within a population

Question 34

genetic drift

Answer 34

• random process
• causes gene frequencies to change over time
• in the absence of natural selection, results in evolution in a population

Question 35

selection

Answer 35

• basis of fitness

- non-random difference in survival/reproduction of individuals based on their fitness