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Related Concept Videos

Reaction Mechanisms03:06

Reaction Mechanisms

Chemical reactions often occur in a stepwise fashion, involving two or more distinct reactions taking place in a sequence. A balanced equation indicates the reacting species and the product species, but it reveals no details about how the reaction occurs at the molecular level. The reaction mechanism (or reaction path) provides details regarding the precise, step-by-step process by which a reaction occurs.
For instance, the decomposition of ozone appears to follow a mechanism with two steps:
Multi-Step Reactions02:31

Multi-Step Reactions

Chemical reactions often occur in a stepwise fashion involving two or more distinct reactions taking place in a sequence. A balanced equation indicates the reacting species and the product species, but it reveals no details about how the reaction occurs at the molecular level. The reaction mechanism (or reaction path) provides details regarding the precise, step-by-step process by which a reaction occurs. Each of the steps in a reaction mechanism is called an elementary reaction. These...
Introduction to Mechanisms of Enzyme Catalysis01:13

Introduction to Mechanisms of Enzyme Catalysis

For many years, scientists thought that enzyme-substrate binding took place in a simple "lock-and-key" fashion. This model stated that the enzyme and substrate fit together perfectly in one instantaneous step. However, current research supports a more refined view scientists call induced fit. The induced-fit model expands upon the lock-and-key model by describing a more dynamic interaction between enzyme and substrate. As the enzyme and substrate come together, their interaction causes a mild...
Phase II Reactions: Methylation Reactions01:17

Phase II Reactions: Methylation Reactions

Methylation is a phase II biotransformation process involving the attachment of a methyl group to a substrate. Enzymes known as methyltransferases orchestrate this reaction.
The mechanism of methylation unfolds in two stages. The first stage sees a methyltransferase enzyme facilitating the transfer of a methyl group from S-adenosylmethionine (SAM) to the substrate, forming S-adenosylhomocysteine (SAH). The second stage involves further metabolism of SAH into homocysteine, which can be recycled...
Catalysis01:27

Catalysis

Catalysis influences the rate of chemical reactions by providing an alternative reaction pathway with lower activation energy. A catalyst speeds up a reaction, but it is not consumed during the process. The fundamental principle of catalysis is the ability of a catalyst to alter the reaction mechanism, often introducing a more efficient pathway than the uncatalyzed process.In a catalyzed reaction, the catalyst participates directly in the reaction mechanism. It interacts with reactants to form...
Catalysis02:50

Catalysis

The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.

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Related Experiment Video

Updated: Jun 24, 2026

Identification of Intracellular Signaling Events Induced in Viable Cells by Interaction with Neighboring Cells Undergoing Apoptotic Cell Death
09:18

Identification of Intracellular Signaling Events Induced in Viable Cells by Interaction with Neighboring Cells Undergoing Apoptotic Cell Death

Published on: December 27, 2016

Mediation and mechanism.

Tyler J VanderWeele1

  • 1Department of Health Studies, University of Chicago, Chicago, IL 60637, USA. vanderweele@uchicago.edu

European Journal of Epidemiology
|March 31, 2009
PubMed
Summary
This summary is machine-generated.

This study clarifies mediation and mechanism in causal inference. Mediation implies mechanism, but the reverse is not always true, impacting statistical and mechanistic causality distinctions.

Related Experiment Videos

Last Updated: Jun 24, 2026

Identification of Intracellular Signaling Events Induced in Viable Cells by Interaction with Neighboring Cells Undergoing Apoptotic Cell Death
09:18

Identification of Intracellular Signaling Events Induced in Viable Cells by Interaction with Neighboring Cells Undergoing Apoptotic Cell Death

Published on: December 27, 2016

Area of Science:

  • Causal Inference
  • Statistical Methodology
  • Philosophy of Science

Background:

  • Distinguishing between mediation and mechanism is crucial in causal inference.
  • Existing formalizations for mediation (counterfactuals) and mechanism (sufficient causes) differ.
  • Recent causal inference methods blur the lines between statistical and mechanistic causality.

Purpose of the Study:

  • To contrast the concepts of mediation and mechanism.
  • To describe the logical implications between mediation and mechanism.
  • To discuss the impact of recent causal inference work on these distinctions.

Main Methods:

  • Formalizing mediation using counterfactual definitions of indirect effects.
  • Formalizing mechanism within the sufficient cause framework.
  • Illustrating both concepts using a single causal diagram.

Main Results:

  • Mediation implies mechanism.
  • Mechanism does not necessarily imply mediation.
  • Both concepts can be represented within a unified causal diagram.

Conclusions:

  • The distinction between statistical and mechanistic causality is challenged by modern causal inference techniques for mediation and mechanism analysis.
  • A clear understanding of the relationship between mediation and mechanism is essential for accurate causal interpretation.
  • Formalization through counterfactuals and sufficient causes provides a rigorous framework for analyzing these concepts.