Topic 1 Flashcards
Why are RNA able to do well at genetic stage AND catalysis
• RNA can catalyze reactions just like proteins.
• RNA can base pair, form double-stranded structures just like
DNA (can also store genetic information)
Some evolutionary forces start to kick in for the development of RNA
- Improved replication
- Simple functions (stability, binding other molecules)
- More complex functions (enzymes)
Eventually, RNA was able to
- Self-replicating RNA (RNA replicase ribozyme)
- Binding amino acids/oligopeptides (stabilize RNA structures/functions) – protein building blocks become more important
- Simple ribosomes that make useful peptides
- More complex proteins
- Introduction of DNA (similar to RNA, more stable.Better long-term genetic storage) o
- “Cell” compartmentalization. RNA/proteins that facilitate these structures
RNA can form intricate, stable structures that can:
- Carry out a wide range of chemical reactions
- Specifically bind many molecules
Proteins are still made today using RNA components
- tRNA
- The active component of ribosomes is a catalytic RNA (proteins = accessory factors, RNA = core of ribosome).
Many apparent “relics” from RNA world
- Common biological molecules with ribonucleotide components (see next slide)
- Various ribozymes (RNA enzymes), riboswitches (mRNA“receptors” that bind ligands – regulate gene expression),
the ribosome itself!
Wheredid the first microbe evolve?
• Precursors to life emerged ~4 bya • We do not know where, but one hypothesis is hydrothermal systems on ocean flood • Stable environment, low UV light, compartments (“cells”), energy, organic molecules (incl. RNA nucleotides)
Last Universal Common Ancestor (LUCA)
- DNA replication, transcription, translation, cell division
- ATP served as energy intermediate
- Lipid bilayer membrane.
- Anaerobic metabolism (no oxygen!) – likely used H2 as energy source, CO2 as carbon source
Chemotroph:
Derive energy from releasing bond energy from chemical compounds
Phototroph:
Absorbs light, transforms it into chemical energy
Chemoorganotrophs
Consume organic chemical for energy
Chemolithotrophs
Consumes inorganic chemicals for energy
The rise of oxygen on earth
• For the first ~ 2 billion years on
earth, the atmosphere was devoid of
oxygen (“anoxic”)
• Oxygen in atmosphere made ideal
electron acceptor – gave rise to
aerobic organisms • Also ozone (O3) layer – protects vs.UV (lethal to cells, damages DNA)
Rise of photosynthetic bacteria that
use sunlight as energy, producing
oxygen as a waste product
(cyanobacteria) - oxygenic
photosynthesis
The endosymbiotic theory
- It is widely agreed that Eukaryotes emerged when an archaea-like ancestor engulfed a bacterium that became an endosymbiont (organism living within another organism in symbiotic relationship)
- Eventually this bacterium became the mitochondria (and transferred many bacterial genes into host organism)
- Plants emerged in a second event when an engulfed photosynthetic bacterium became basis for chloroplast
