Sigam o Carbono -2

Four types of organic macromolecules in living systems. Most of the molecules in the living systems are water (H 2 O) and large organic macromolecules: Carbohydrates Lipids Proteins Nucleic Acids

Carbohydrates (sugars, starches) Representatives: Glucose, Fructose Many hydroxyl groups (-OH) Soluble in water Form Polysaccharides Good energy source Structural support for organisms (cellulose - the main constituent of wood)

Glucose Fructose Table sugar

Glucose polymerization In starch molecule (potato) there can be 100s thousands of glucose units H2OH2O Linked by dehydration reaction Polysaccharides

Carbohydrates are important as a source of energy for life Respiration CH 2 O + O 2 → CO 2 + H 2 O + Energy In reality: C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O +Energy Fermentation C 6 H 12 O 6 → 2CO 2 + 2C 2 H 6 O + Energy

But there are ways to get energy without carbohydrates. Methanogenesis CO H 2 → CH 4 + 2H 2 O + Energy Sulfate reduction 4H 2 + SO 4 2- → S H 2 O + Energy

Lipids (fats and oils) Representatives: fatty acids and cholesterol Poorly soluble Good (concentrated) energy source Flexible (cell membrane material)

Some lipids have hydrophilic (love water) head and hydrophobic tail In solution these lipids can form monolayers, bilayers and bilayer vesicles spontaneously – pre-cells. Lipids are important for the formation of the cell membrane

Monolayer Bilayer Bilayer vesicle Micells

Membrane Lipids are very complex

Cell Membrane Lipids

ORIGINS OF LIFE?

Two Approaches to the origin of life “Top-down strategy” is to look at the present day biology and extrapolate (project) back towards the simplest living entities. “Bottom-up strategy” is to make the complex building blocks of life (organic macromolecules) and put them together.

Cells are very diverse in size, shape and complexity but there are 2 basic cell types Prokaryotes are much simpler and smaller than eukaryotes Eukaryotes have a cell nucleus (to protect DNA) while prokaryotes do not Prokaryotes are single-celled only Eukaryotes may be either single-celled or multicellular Top-down strategy: How would the most ancient cell look like?

Prokaryotes

Eukaryotic cell

Eukaryotes vs. Prokaryotes Who outnumbers and outweighs the other? Who is more dependent on the other?

Eukaryotes look much more complex then prokaryotes. Do we see the difference in the DNA structure? Yes

Is the genome (order of nucleotides) of Eukaryotes and Prokaryotes completely different? No Some parts of the genome change more easily than others in the course of evolution A segment of the DNA responsible for coding of ribosomal parts (16S RNA, 1500 nucleotides) is very well conserved.

A part of the gene for 16S RNA (~1500 nucleotides) for different organisms. Corresponding segments of nucleotide sequence from an archaean (Methanococcus jannaschii), a eubacterium (Escherichia coli) and a eucaryote (Homo sapiens) are aligned in parallel. Sites where the nucleotides are identical between species are indicated by a vertical line. Genetic information conserved since the beginnings of life.

Top-down strategy: The Tree of Life By looking at the changes in 16S RNA we can identify three domains of life Bacteria, Archaea, and Eucaryotes Prokaryotes

“Bottom-up” strategy to the origin of life is to make complex building blocks of life and try to put them together. But first we need to answer how was it possible to make any organic molecules at all without biology? Bottom-up strategy

EARTH TODAY Abiotic synthetic reactions on the early Earth Prebiotic soup Prebiotic polymers The origin of life RNA world Protein/DNA world (modern biochemistry) Organics from space Bada & Lazcano (Science, 2002)

Problems with abiotic organic synthesis. Almost all organic carbon which we observe today is produced biologically (photosynthesis): CO 2 + H 2 O  CH 2 O + O 2 Carbon which comes out of volcanoes is in a form of CO 2 CO 2 gas mixture does not produce organic molecules on its own inorganic organic

Terrestrial vs. Extraterrestrial Terrestrial origin – organic synthesis occurred somewhere in the Earth environment Extraterrestrial origin – organic material was synthesized in space and was brought to Earth somehow

Urey-Miller Experiment 1) At some point scientists believed that the ancient atmosphere was rich in CH 4 and NH 3 2) But! Just mixing CH 4, NH 3, H 2 O, H 2 would not produce any organic material 3) Miller showed that a spark discharge (lightning) would produce organic molecules up to 10-15% of the initial CH 4 by mass

The Miller-Urey-Experiment FIRST EXPERIMENTAL FORMATION OF BIOLOGICALLY RELEVANT MOLECULES UNDER PREBIOTIC CONDIDTIONS

Formation of organic molecules in the gas phase UV can be used for organic synthesis as well The key is to produce carbon radicals CH 4 + h  CH 3 + H CH 3 + CH 3  C 2 H 6 + M C 2 H 6 + h C 2 H C 2n H 2 + C 2 H  C 2n+2 H 2 + H Polymerization is extremely sensitive to O abundance

Titan’s Organic Haze Layer Haze is thought to form from photolysis (and charged particle irradiation) of CH 4 (Picture from Voyager 2)

Advantages of Organic synthesis in the ancient atmosphere UM-like experiments produced many types of organic molecules which are used in proteins We would expect lightning and UV radiation in the prebiotic atmosphere No need to deliver organic material to Earth – it would be already here

Difficulties for the organic synthesis via UM experiment It is hard to justify large amounts of NH 3 and CH 4 in the prebiotic atmosphere In the CO 2 -rich atmosphere organic production by spark discharge is not very efficient If CH 4 /CO 2 < 0.1 essentially no organic production

Trainer et al., 2005; 2006)

Hydrothermal vents Fischer-Tropsch synthesis. Under high temperatures and pressures CO and H 2 can form hydrocarbons (2n+1)H 2 + nCO → C n H (2n+2) + nH 2 O where 'n' is a positive integer

Advantages of Organic synthesis in the Hydrothermal Vents Hydrothermal vents were likely to be present in the prebiotic environment Organic synthesis requires only CO 2, H 2 O and silicate rocks. Serpentinization: Spinel polymerization: Olivine SerpentineMagnetite (spinel group)

Difficulties of the organic synthesis via Hydrothermal Vents No clean catalysts in nature. Original Fischer- Tropsch reaction goes fast in the presence of iron and cobalt Only very simple organics can be generated. No amino-acids, no PAHs etc.

Since both atmosphere and hydrothermal vents have problems producing organics we need to look somewhere else. Space!

Hale-BoppMurchinson Gaseous Pillars – Eagle Nebula Key hole Nebula Titan