Primitive bio-chemistry to molecular biology ASTR 3300 Guest Lecture by Bonnie Meinke September 2, 2009 ASTR 3300 Guest Lecture by Bonnie Meinke September 2, 2009

RNA world Chicken and egg paradox: how could one of the key molecules (DNA, RNA, and protein enzymes) have existed without the other two? Discovery in the mid-1980s: RNA has catalysts (ribozymes), which means a simpler RNA world may preceded the DNA and protein world

RNA world evidence for an early RNA world: RNA nucleotides are more readily synthesized than DNA nucleotides DNA could have evolved from RNA and taken hold because of its greater stability RNA must have evolved before proteins because proteins cannot replicate in absence of RNA

RNA world simple RNA organisms eventually began transcribing DNA DNA is a more efficient replicator, so it outcompeted RNA via natural selection

viruses are parasites made of nucleic acid encased in protein coats once inside a host organism, viruses hijack its chemical energy and replicates itself retroviruses reverse cellular processes by transcribing RNA into DNA, which instructs the cell to produce more viral RNA HIV HPV RNA and retroviruses

Primitive Biochemistries Organisms require energy source Organisms that create organic matter from energy and inorganic substances are called autotrophs What are the energy sources autotrophs utilize?

Primitive Biochemistries Organisms require energy source Organisms that create organic matter from energy and inorganic substances are called autotrophs What are the energy sources autotrophs utilize?  Light  Chemicals

Energy Sources Most important energy source for Earth is the sun: Photosynthesis uses light energy to produce sugars and oxygen from water and carbon dioxide nCO 2 + nH 2 O + energy  (CH2O) n + nO 2 Mid-ocean hydrothermal vents: chemosynthesis Chemical energy is utilized in this process. Superheated water dissolved minerals in rock, which organisms living near such vents use to create organic compounds.

Metabolism Two most common metabolisms on Earth today: Fermentation Carbohydrate glucose  CO 2 + ethanol/ lactic acid + energy Only extracts 2 phosphate bonds’ worth of energy Respiration (CH 2 O) n + nO 2  nCO 2 + H 2 O + energy Extracts a whopping 36 phosphate bonds’ worth of energy! Much more efficient than fermentation

Molecular phylogeny Top-down approach to extrapolate origin of life (~ 4 Ga) from current biosphere Phylogenetic trees show that evolution allows life to build on what has worked Method involved in constructing a tree involves examining similar molecules in different organisms and comparing to trace a common ancestor

Phylogenic tree from ribosomal RNA Life broken into 3 domains Bacteria Archaea Eukarya

Tree of Life Thermophiles and hyperthermophiles lie near roots of branches - life has evolved from high to low temperature environments Organisms near roots also use energy source other than light This means last common ancestor was likely a heat-loving chemosynthetic organism such as those in hydrothermal vents today (thermophile - to be discussed week after next)