Which effect occurs when the master molecule is struck by radiation?

Which effect occurs when the master molecule is struck by radiation?

• A. Indirect effect
• B. Target theory
• C. Direct effect
• D. Doubling dose

Answer: (C)

The main idea here is whether radiation damages the cell by hitting the genetic material directly. When the master molecule, typically DNA, is struck by radiation, energy is deposited inside that molecule itself, causing ionization and direct damage such as strand breaks or base changes. This is the direct effect, where the target molecule—the DNA—receives the hit. In contrast, indirect effects occur when radiation mainly ionizes surrounding water molecules, producing reactive radicals that then go on to damage DNA. The direct effect is more likely when energy is absorbed directly by the DNA, which can depend on the type of radiation (high-LET more often produces direct hits) and the cellular context. The other concepts relate to different ideas: target theory describes the idea of a critical target within the cell that must be hit to produce an effect, and the doubling dose is a genetic concept about the dose needed to double the incidence of a hereditary effect in a population.

The main idea here is whether radiation damages the cell by hitting the genetic material directly. When the master molecule, typically DNA, is struck by radiation, energy is deposited inside that molecule itself, causing ionization and direct damage such as strand breaks or base changes. This is the direct effect, where the target molecule—the DNA—receives the hit.

In contrast, indirect effects occur when radiation mainly ionizes surrounding water molecules, producing reactive radicals that then go on to damage DNA. The direct effect is more likely when energy is absorbed directly by the DNA, which can depend on the type of radiation (high-LET more often produces direct hits) and the cellular context. The other concepts relate to different ideas: target theory describes the idea of a critical target within the cell that must be hit to produce an effect, and the doubling dose is a genetic concept about the dose needed to double the incidence of a hereditary effect in a population.