Joel Huberman and Arthur Riggs used pulse–chase labeling to examine the replication of DNA in mammalian cells. Briefly describe the Huberman–Riggs experiment, and identify how the results exclude a unidirectional model of DNA replication.

Key Concepts

Pulse-Chase Labeling

Pulse-chase labeling is a technique used to study the dynamics of biological molecules, particularly DNA and proteins. In this method, cells are exposed to a labeled compound (the 'pulse') for a short time, allowing the incorporation of the label into newly synthesized molecules. After this period, the labeled compound is replaced with an unlabeled one (the 'chase'), enabling researchers to track the fate of the labeled molecules over time.

DNA Replication Models

DNA replication can occur through different models, including unidirectional and bidirectional replication. The unidirectional model suggests that DNA strands are replicated in one direction only, while the bidirectional model posits that replication occurs simultaneously in both directions from a replication origin. Understanding these models is crucial for interpreting experimental results related to DNA synthesis.

Huberman-Riggs Experiment

The Huberman-Riggs experiment involved using pulse-chase labeling to track the replication of DNA in mammalian cells. Their findings demonstrated that newly synthesized DNA strands were labeled in both directions from the origin of replication, indicating that replication occurs bidirectionally. This result effectively excluded the unidirectional model, as it showed that DNA replication is a more complex process involving simultaneous synthesis on both strands.