DNA & Polypeptide Synthesis

Introduction

DNA and polypeptide synthesis are key biological processes vital for cellular function and heredity. This guide details the structural distinctions and synthesis mechanisms in prokaryotes and eukaryotes, providing insights into their genetic processes.

Overview of DNA Structure and Role

• DNA Structure: DNA is a double helix comprised of base pairs: adenine-thymine and cytosine-guanine.
• Function: Stores genetic information critical for inheritance.
• Replication ensures genetic fidelity through the precise duplication of DNA.

Polypeptide Synthesis

• Definition: The process of forming proteins from nucleotide sequences; amino acids serve as building blocks.
• Importance: Proteins are indispensable for:
  • Enzymatic activity
  • Structural support
  • Immune responses
  • Errors in synthesis can lead to disorders, such as sickle cell anaemia.

Central Dogma of Molecular Biology

• Flow of genetic information: DNA → RNA → Protein
  • Transcription: Conversion of DNA to RNA.
  • Translation: Conversion of RNA to Protein.

DNA in Prokaryotes

• Structure: Features a single, circular chromosome located in the nucleoid.
• Packaging Mechanism:
  • Supercoiling compacts DNA.
  • Absence of histones streamlines packaging, facilitating replication for adaptability.
• Plasmids:
  • Small, circular DNA contributing to survival (e.g., antibiotic resistance).

DNA in Eukaryotes

• Structure: Composed of linear chromosomes with intricate packaging.
• Nucleosomes:
  • DNA wrapped around histones.
  • Essential for DNA compaction and regulation.

DNA Replication: Prokaryotes vs. Eukaryotes

• Prokaryotes: Features a single origin of replication. Enzymatic cooperation, including helicase and DNA polymerase, enables rapid replication.
• Eukaryotes: Possess multiple replication origins, involving complex machinery with DNA polymerases α, ε, δ.

Eukaryotic Replication Challenges

• End-Replication Problem: Telomerase plays a crucial role in maintaining chromosome ends.

Transcription and Gene Expression

• Prokaryotes:
  • Simultaneous transcription and translation allow for rapid response.
  • Use operons for coordinated gene expression (e.g., LAC Operon).
• Eukaryotes:
  • Involves features like introns/exons and regulatory sequences like enhancers/silencers.
  • Processes include splicing and RNA modifications.

Comparison of DNA Features

Aspect	Prokaryotes	Eukaryotes
Cellular Location	Nucleoid	Nucleus
Chromosome Structure	Circular	Linear
DNA Packaging	Supercoiling	Histones/Chromatin
Replication Machinery	Simpler	Complex
Gene Expression	Operons	Regulatory Elements

Implications and Applications

• Antibiotic Development: Focuses on targeting bacterial replication.
• Biotechnological Advancements: Innovations such as CRISPR and genetic engineering leverage insights from these processes.