RNA World Flashcards
(28 cards)
What is the central dogma as we know it?
-Replication
-Catalysis
-Mutability
Summarization of the basics of the origin of life
-Growth in complexity enables organisms to out-compete each other
-Life started from a single point
-Originator looked very different from life today
-Conditions of Earth (the pond) allowed for an exit from the prebiotic soup (chemical to biological)
Why are DNA mutations important?
-Enable novelty
-Are heritable
Why are most mutations not helpful?
-Mutation is (mostly) random
-The genetic code is degenerate, some mutations are silent
-Many mutations inactivate proteins
-Mutations that alter function are rare
What happens when there is a good mutation?
-Mutation occurs in a germ cell
-Expressed in offspring
-Offspring survive between
-More organisms with mutations
Where did the first clue of relatedness of distant organisms come from?
-Macroscopic observations
-Ex: fossils
What is convergent evolution
-Macroscopic observations are undermined by convergent evolution
-Convergent evolution describes when distant organisms evolve similar traits independently
-Can be obvious (evolution of flight)
-Can be cryptic (marsupials and placental mammals)
What is divergent evolution and how does it work
-When organisms evolve divergently from a common ancestor
-Common ancestors are usually hypothetical because we can only study present day organisms
-Nodes of genetic trees are common ancestors
-Organizing a genetic tree relies on distinguishing convergent and divergent evolution
What does convergent evolution look like on a molecular scale?
-Virtually impossible for two proteins to evolve to adopt the same structure by convergent evolution
-If proteins show structural similarity they arose through divergent evolution
-Chymotrypsin and Subtilisin
—Have virtually identical catalytic triads
—Catalyze peptide bond cleavage
—Proteins adopt distinct folds
What are missense, nonsense, and silent mutations
-Missense: mutation changes an amino acid
-Nonsense: Premature stop codon
-Silent: Same amino acid despite mutation
What can be used to determine relatedness of proteins?
-DNA sequence
-Protein structure is defined by DNA sequence
What can be used to build the genetic tree of life?
-DNA sequences of highly conserved proteins and rRNA
What is LUCA
-Last Universal Common Ancestor
Why is there no DNA world?
-DNA is maintained double stranded and inert
-DNA is less reactive
-No natural DNA-based enzymes
Why is there no protein world
-No mechanism to store information and faithfully replicate
-rRNA, not protein, is required for protein synthesis
What is the evidence for the RNA world?
-RNA provides information storage
—Base-pairing provides a mechanism to replicate the genome
—Replication can, in principle, occur spontaneously (albeit slowly)
-RNAs can catalyze virtually any reaction
-RNA relics can be found throughout life
-Building blocks for DNA (dNTPs) are synthesized from rNTP precursors
What is the model of the RNA world?
-Primordial ribosomes may have been entirely RNA
-A cooperative relationship between RNA and protein might have arisen when proteins could increase the efficiency and/or accuracy of RNA synthesis
-Perhaps RNA was the primary substance of life, the participation of proteins were later refinements that increased Darwinian fitness of an already established self-replicating system
What are the arguments against the RNA world?
-RNA is unstable
-Building blocks of RNA had to come from somewhere
-How would synthesis of long 3’ to 5’ linkages compete with 2’ to 5’ or 5’ to 5’ linkages
Was RNA the first molecule of its kind?
-Unlikely
-More likely that first molecules had catalytic activity and information storage capabilities, but may have been polymers that resemble RNA, but were chemically simpler
-There was a world before RNA
What elements were living systems made up of?
-Most organisms are ~70% water
-No biological requirement for 64 of the 90 naturally occurring elements
-Major roles for C, O, and N
-Living systems are very different from the Earth’s crust
Why is carbon so important?
-It is very versatile
-Can form up to four covalent bonds, and single, double, and triple bonds
—Allows for many combinations and pendent side chains (3 or more bonds)
What other elements could be used on the place of carbon?
B, N, Si, P
Why was carbon selected for over the other feasible elements
-C-C bonds are very strong
-C-N-C or C-O-C or C-O-P-O-C are weaker, enabling enzymatic destruction at specific sites
-Other elements have less ideal bond energies
What were the prebiotic conditions?
-~4.5 billion years ago, Earth would finally have a stable atmosphere and oceans
-Almost no oxygen (highly reactive and there was no life)
-Primarily H2O, N2, CO2
-Smaller amounts of CH4, NH3, SO2, and H2
