BI110 Lecture Notes - Lecture 5: Thomas Cech, Reducing Atmosphere, Macromolecule
Biologically important Macromolecules
4 major types of macromolecules important for all forms of life
Nucleic acids (DNA & RNA)
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Proteins
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Lipids
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Carbohydrates
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All except lipids are polymers made up form simpler building blocks, and
all are made within cells by complex metabolic pathways
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Formation of biologically important molecules
Organic molecules that form building blocks of life could have been
formed in conditions that prevailed on primitive earth
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Reducing atmosphere that lacked oxygen
H2S, CO2, NH3, CH4, H2O(vapor)
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Allows for synthesis of complex organic molecules
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Miller-Urey Experiment
Simulated Earth's early conditions and created several organic molecules
including amino acids
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When HCN and CH2O were added, lipids, sugars, and nucleotide
components were generated too
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Protocells: The First Cells
Protocells (or photobionts): group of abiotically-produced organic
molecules that are surrounded by a membrane or membrane-like
structure
Can form spontaneously
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Primitive cell-like structures
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Some properties of life
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May have been precursors of cells
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The Central Dogma
DNA (information is stored in DNA) --> RNA (the information in DNA is copied
into RNA) --> Protein( the information in RNA guides the production of proteins)
Ribozymes
Ribozymes:+RNA+molecules+that+catalyze+specific+reactions+
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DNA+and+proteins+may+have+evolved+after+RNA+
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Discovered+by+Thomas+Cech+
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Scenario for Evolution of Flow of Information
Proteins and DNA
Proteins became dominant structural and functional macromolecule of all
cells
Greater diversity
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Much higher rate of catalysis
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DNA is double-stranded and more stable than RNA and thus evolved as
better repository of genetic information
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Alternatives to the RNA World Hypothesis
It probably wasn’t just RNA -
Earliest forms of Life
Earliest forms of life were most likely simple prokaryotes
Earliest fossil evidence : 3.5 billion years ago
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Indirect evidence (carbon isotope ratios): 3.9 BYA
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Earliest prokaryotes
Heterotrophs (as opposed to autotrophs)
Use anaerobic respiration to extract energy
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The first autotrophs performed an oxygenic photosynthesis
Used H2S instead of H2O
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Oxygenation of the atmosphere
Atmospheric oxygen began increasing approx. 2.5 BYA-
Due to cyanobacteria that evolved the ability to use H2O instead of H2S
as the source of electrons
Oxygenic photosynthesis
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Module 73 & 74
Document Summary
4 major types of macromolecules important for all forms of life. All except lipids are polymers made up form simpler building blocks, and all are made within cells by complex metabolic pathways. Organic molecules that form building blocks of life could have been formed in conditions that prevailed on primitive earth. Simulated earth"s early conditions and created several organic molecules including amino acids. When hcn and ch2o were added, lipids, sugars, and nucleotide components were generated too. Protocells (or photobionts): group of abiotically-produced organic molecules that are surrounded by a membrane or membrane-like structure. Dna (information is stored in dna) --> rna (the information in dna is copied into rna) --> protein( the information in rna guides the production of proteins) Dna and proteins may have evolved after rna. Proteins became dominant structural and functional macromolecule of all cells. Dna is double-stranded and more stable than rna and thus evolved as better repository of genetic information.
