Primitive bio-chemistry to

molecular biology

Primitive bio-chemistry to

molecular biologyASTR 3300

Guest Lecture by Bonnie MeinkeSeptember 2, 2009

ASTR 3300Guest Lecture by Bonnie Meinke

September 2, 2009

RNA worldRNA 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 worldRNA 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 worldRNA worldsimple 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

RNA and retroviruses

Primitive Biochemistries

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

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 SourcesEnergy SourcesMost important energy source for Earth is the sun: Photosynthesis

uses light energy to produce sugars and oxygen from water and carbon dioxide

nCO2 + nH2O + energy (CH2O)n + nO2

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.

MetabolismMetabolism• Two most common metabolisms on Earth today:

• Fermentation

• Carbohydrate glucose CO2 + ethanol/ lactic acid + energy

• Only extracts 2 phosphate bonds’ worth of energy

• Respiration

• (CH2O)n + nO2 nCO2 + H2O + energy

• Extracts a whopping 36 phosphate bonds’ worth of energy!

• Much more efficient than fermentation

Molecular phylogenyMolecular 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

Phylogenic tree from ribosomal RNA

Life broken into 3 domains

Bacteria

Archaea

Eukarya

Tree of LifeTree of LifeThermophiles 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)