Initiation

Definition

Initiation is the first and critical step in various processes, marking the beginning of a sequence of events or reactions. This term is particularly relevant in the contexts of radical additions to alkenes, radical halogenation of alkanes, transcription of DNA, and translation of RNA during protein biosynthesis.

5 Must Know Facts For Your Next Test

1. In radical additions to alkenes, initiation involves the formation of a reactive radical species, typically through the homolytic cleavage of a covalent bond.
2. Radical halogenation of alkanes is initiated by the formation of a halogen radical, often through the photolysis or thermal decomposition of a halogen molecule.
3. Transcription of DNA is initiated when RNA polymerase binds to a promoter sequence on the DNA, signaling the start of the RNA synthesis process.
4. Translation of RNA is initiated when the small ribosomal subunit binds to the mRNA, recognizing the start codon and positioning the ribosome to begin protein synthesis.
5. Initiation is a crucial step in these processes, as it sets the stage for the subsequent chain of events or reactions to occur.

Review Questions

• Describe the role of initiation in the context of radical additions to alkenes and the formation of chain-growth polymers.
  • In radical additions to alkenes, the initiation step involves the formation of a reactive radical species, typically through the homolytic cleavage of a covalent bond. This initial radical then adds to the alkene, generating a new radical that can propagate the chain reaction. The propagation steps lead to the formation of chain-growth polymers, where the growing polymer chain continues to add monomer units. The initiation step is crucial in this process, as it kickstarts the chain reaction and sets the stage for the subsequent polymerization.
• Explain how the initiation step in radical halogenation of alkanes is different from the initiation in radical additions to alkenes.
  • The initiation step in radical halogenation of alkanes differs from the initiation in radical additions to alkenes. In radical halogenation, the initiation typically involves the formation of a halogen radical, often through the photolysis or thermal decomposition of a halogen molecule. This halogen radical then abstracts a hydrogen atom from the alkane, generating a new alkyl radical that can propagate the chain reaction. In contrast, the initiation in radical additions to alkenes involves the formation of a reactive radical species through the homolytic cleavage of a covalent bond, which then adds to the alkene. The distinct initiation steps lead to different chain reaction mechanisms and products in these two processes.
• Analyze the role of initiation in the transcription of DNA and the translation of RNA during protein biosynthesis, and explain how these initiation steps are interconnected.
  • The initiation steps in transcription and translation are critical for the overall process of protein biosynthesis. In transcription, the initiation occurs when RNA polymerase binds to a promoter sequence on the DNA, signaling the start of the RNA synthesis process. This initiates the transcription of the genetic information from DNA to RNA. In translation, the initiation step involves the small ribosomal subunit binding to the mRNA, recognizing the start codon and positioning the ribosome to begin protein synthesis. These two initiation steps are interconnected, as the mRNA produced during transcription serves as the template for the translation process. The successful initiation of both transcription and translation is essential for the accurate and efficient production of proteins, which are the fundamental building blocks of life.

Related terms

Chain Reaction:

A series of interconnected reactions where the products of one step trigger the next, leading to a self-propagating process.

Propagation:

The continuation of a chain reaction, where reactive intermediates react with other molecules to generate new reactive species.

Termination: The final step in a chain reaction, where reactive intermediates are consumed, and the reaction is stopped.