| Chem 431 |
Biochemistry |
Fall 2007 |
| Lecture Notes: 29 August |
© R. Paselk 2007 |
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Origin of Life, cont.
The biggest problem for the origin of life is the issue of how we go from polymers to living "systems."
- Consider the problem of protein biosynthesis:
- Going from DNA (information archive) to RNA (usable information) requires a rather complex system to assure accurate transcription today. However, we could assume a much simpler system in the early, low-competition, Earth.
- Going from RNA to protein incredibly complex:
- Need adaptor molecules (t-RNA) because there isn't any natural relationship between RNA codes (sequences) and particular amino acids.
- Need enzymes to match specific amino acids to specific tRNA's because even the tRNA's are not specific to amino acids in term of recognizing them.
- as a result, need 20 tRNAs + 20 proteins!
- Need a complex molecular machine, the Ribosome, to read off the mRNA message using the tRNAs and make proteins:
- Ribosome consists of
- 1-2 small RNAs + two large, complexly folded, RNAs,
- 50-100 accesory proteins.
- The chance of such a system arising spontaneously is truly infinitesimal.
- "RNA World" has been potulated to solve these dificulties. (text Figure 1-34)
- In this scenario RNA-based life preceeds "modern" life.
- First "life" combined information and catalytic properties in single RNA-protein molecules.
- Later there was a transition where proteins took over much of machinery over time.
Pre-Cambrian Life:1 (text Figure 1-35)
- 3.8 - microfossils?
- 3.46 - stomatolites (Australia) [3.5-3.3 microfossils of cyanobacteria?]
- 2.8 kerogens with low 13C/12C indicative of O2 use by methanogens
- 2.7-2.5 2-methyl-hopane "fossils" (cyanobacterial markers); steranes (eukaryotic molecular marker, oxygen needed for synthesis)
- Origin of eukaryotes (text Figure 1-36)
- 2.5 -> stromatolite reefs rivaling modern reefs in size and architecture
- 0.6 Ediacaran fauna
- 0.54-0.53 "Cambrian explosion"
DNA vs. Fossils
1A slightly enhanced treatment, with photos of specimens at our natural history museum is available by clicking on the link.
Chapter 2: Water
Water is a very unusual, even incredible substance whose amazing properties are often unappreciated because of its ubiquitousness. Water's special properties include extremely high mp and bp (0 °C & 100 °C K, compare to methane, -183 °C & -161 °C, with a MW of 16 vs. water's 18); a high heat capacity (18 cal/°C mol vs. 8 cal/°C mol for methane); it has a high viscosity; its solid form is less dense than the liquid form at the same temperature (ice floats on water - very rare), it has a large surface tension, and it has a high dielectric constant (78.5 vs. 1.9 for hexane).
The high mp, bp, and heat capacity of water all predict relatively strong bonding between water molecules, so let's first review the types of bonding which occur between atoms and molecules. The most stable bonds are of course covalent bonds (with bond energies of 50 [S-S] to 80 [C-C] to 110 [O-H] kcal/mol), occurring when we have significant overlap of atomic orbitals.
Last modified 29 August 2007
Pathway Diagrams
