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Difficulty: MediumComparing and Contrasting Models

### Hypotheses on the Origin of Life

#### Model 1 (RNA World Hypothesis)
The RNA World hypothesis proposes that self-replicating ribonucleic acid (RNA) molecules were the precursors to modern life. In this model, RNA served both as the genetic material (storing information) and as a catalyst for chemical reactions (similar to modern protein enzymes called ribozymes). Over time, DNA took over the role of genetic storage due to its greater chemical stability, and proteins became the primary catalysts because of their greater chemical versatility. RNA-based systems evolved in prebiotic aqueous environments rich in nucleotides, requiring external energy sources such as ultraviolet (UV) radiation from the Sun to drive the synthesis of nucleotides and other organic compounds.

#### Model 2 (Iron-Sulfur World Hypothesis)
The Iron-Sulfur World hypothesis proposes that life originated near deep-sea hydrothermal vents. According to this metabolism-first model, the earliest life-like systems were mineral-based metabolic networks that did not rely on self-replicating genetic polymers initially. Instead, geochemical energy—specifically, the temperature and chemical gradients of hot, mineral-rich hydrothermal fluids containing hydrogen sulfide (H2SH_2S) and dissolved iron—drove the synthesis of organic molecules. Iron-sulfur minerals catalyzed the reduction of carbon dioxide (CO2CO_2) into organic molecules through a primitive, non-enzymatic cycle. Genetic systems like RNA and DNA evolved later as late additions to stabilize these existing metabolic pathways.

Based on the models described, match each prebiotic feature or energy source on the left with the correct model classification on the right.

  • Prebiotic catalysis is performed by self-replicating RNA molecules.A catalyst unique to Model 1's prebiotic systems
  • Prebiotic catalysis is performed by transition metal minerals.A catalyst unique to Model 2's prebiotic systems
  • Energy is supplied by solar ultraviolet radiation.The energy source driving prebiotic synthesis in Model 1
  • Energy is supplied by chemical and thermal gradients.The energy source driving prebiotic synthesis in Model 2

Answer

To match the prebiotic features with their correct models, associate the catalysis and energy source described in the text with the corresponding hypothesis. Model 1 is characterized by RNA catalysis and solar ultraviolet radiation, while Model 2 is characterized by mineral catalysis and geothermal gradients.
Matching each prebiotic feature requires identifying the specific catalytic agents and energy sources outlined for each model. Model 1 (RNA World) relies on RNA molecules for catalysis and solar UV for energy, whereas Model 2 (Iron-Sulfur World) relies on transition metal minerals for catalysis and hydrothermal geochemical gradients for energy.

Step-by-Step Solution

1
Locate the catalytic mechanism in Model 1.
Model 1 relies on RNA molecules acting as catalysts.
This links prebiotic catalysis by RNA molecules to Model 1's unique catalyst system.
2
Locate the catalytic mechanism in Model 2.
Model 2 relies on iron-sulfur minerals acting as catalysts.
This links prebiotic catalysis by transition metal minerals to Model 2's unique catalyst system.
3
Locate the primary energy source in Model 1.
Model 1 relies on solar ultraviolet (UV) radiation.
This identifies solar UV radiation as the energy source driving synthesis in Model 1.
4
Locate the primary energy source in Model 2.
Model 2 relies on chemical and thermal gradients of hydrothermal fluids.
This identifies geothermal gradients as the energy source driving synthesis in Model 2.

Key Concept

Comparing and contrasting mechanisms of catalysis and energy transduction in scientific models of prebiotic evolution
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Topics

Comparing and Contrasting Models

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