IB Biology 2.7 DNA Replication, Transcription and Translation Notes

Introduction

In the field of molecular biology, understanding the processes of DNA replication, transcription, and translation is crucial. These processes are fundamental to the flow of genetic information within a cell, often summarized by the central dogma of molecular biology: DNA → RNA → Protein. This study note document will delve into each of these processes in detail, breaking down complex concepts into digestible sections.

DNA Replication

DNA replication is the process by which a cell duplicates its DNA, ensuring that each daughter cell receives an exact copy of the genetic material. This process is semi-conservative, meaning that each new DNA molecule consists of one old (parental) strand and one newly synthesized strand.

Key Steps in DNA Replication

1. Initiation
   • Replication begins at specific locations called origins of replication.
   • Enzymes like helicase unwind the DNA double helix, creating a replication fork.
   • Single-strand binding proteins (SSBs) stabilize the unwound DNA.
2. Elongation
   • Primase synthesizes a short RNA primer to provide a starting point for DNA polymerase.
   • DNA polymerase III adds nucleotides to the 3' end of the RNA primer, synthesizing the new DNA strand.
   • The leading strand is synthesized continuously, while the lagging strand is synthesized in short fragments called Okazaki fragments.
3. Termination
   • DNA polymerase I removes RNA primers and replaces them with DNA.
   • DNA ligase joins the Okazaki fragments on the lagging strand, forming a continuous DNA molecule.

Enzymes Involved

• Helicase: Unwinds the DNA double helix.
• Primase: Synthesizes RNA primers.
• DNA Polymerase III: Adds nucleotides to the growing DNA strand.
• DNA Polymerase I: Removes RNA primers and replaces them with DNA.
• DNA Ligase: Joins Okazaki fragments.

Transcription

Transcription is the process by which the genetic information in DNA is copied into messenger RNA (mRNA). This process occurs in the nucleus of eukaryotic cells.

Key Steps in Transcription

1. Initiation