Biology 1002B Chapter Notes - Chapter 2.3-2.4: Ribozyme, Lipid Bilayer, Nucleic Acid Sequence
29 Apr 2018
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3.3 From Macromolecules to Life
Attributes of a modern cell:
1. A membrane-defined compartment - the cell
2. A system to store genetic info and use it to synthesize proteins
3. Energy-transforming pathways to bring in energy from environment and harness it
to sustain life
3.3a Lipid Spheres May Have Led to the Development of Cells
• Membrane-defined compartment needed for primitive metabolic reactions
• Protobiont: abiotically produced organic molecules surrounded by a membrane
o Could have formed spontaneously without input of energy given conditions
of primordial Earth
o Similar to liposome (vesicle with lipid bilayer)
o Clay accelerates formation of liposomes
o Lipid membrane system must have evolved simultaneously with genetic info
system
3.3b RNA Can Carry Info and Catalyze Reactions
• The central dogma
o Info stored in DNA
o DNA copied into RNA
o RNA guides production of proteins
• Products of this process, proteins, are required to catalyze each step of the
process
• Ribozymes: RNA-based catalyst that is part of biochemical machinery of all cells
o Single-stranded molecules can fold into specific shapes - function like
proteins
o Nucleotide sequence carry info - function like DNA
o Early life existed in an "RNA world"
3.3c RNA is Replaced by DNA and Proteins
• DNA and proteins do a better job than RNA
• Possible development of today's system:
1. First cells only contained RNA
2. RNA evolved and could catalyze formation of proteins before development of
ribosomes
3. DNA nucleotides produced by random removal of oxygen from RNA
nucleotides
4. DNA nucleotides paired with RNA molecules
5. Once DNA copies were made, selection favoured DNA
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