Lecture Notes: Gene Extraction and Synthesis

Introduction

• Gene extraction challenges:
  • Cutting chromosomes with restriction endonucleases is not always feasible.
  • Issues include unsuitable restriction sites and large DNA fragments.
  • Direct cuts on the gene can render it nonfunctional.
  • In eukaryotes, genes contain introns, complicating extraction from chromosomes.

Restriction Endonucleases

• Problems:
  • Inappropriate restriction enzymes may cut far from the gene or directly through it.
  • Eukaryotic genes have introns, which we do not want in the final gene product.

Introns and mRNA

• Gene transcription:
  • Introns are removed during mRNA processing, leaving only exons.
  • Goal is to obtain a gene without introns.

Solving the Problem of Introns

1. mRNA Extraction and Conversion:

   • Extract mRNA which has introns removed.
   • Use reverse transcriptase to convert mRNA back to DNA (cDNA).
   • cDNA is a single-stranded DNA copy from mRNA without introns.
   • Use DNA polymerase to produce double-stranded DNA.

2. Artificial DNA Synthesis:

   • Use a DNA synthesizer to create gene sequences.
   • Input desired DNA sequence into the synthesizer.
   • Machine uses specific DNA nucleotides to synthesize the gene.

Detailed Steps for Gene Extraction Without Introns

• Procedure:
  • Extract mRNA from organism.
  • Utilize reverse transcriptase enzyme to create cDNA.
  • Use DNA polymerase to transform cDNA into double-stranded DNA.

Alternative Gene Synthesis

• Artificial Synthesis via DNA Synthesizer:
  • Define the protein and its corresponding mRNA sequence.
  • Use the mRNA sequence to deduce the DNA template sequence.
  • Input DNA sequence into the synthesizer machine for gene creation.

Summary

• Three methods to obtain genes:
  1. Restriction enzymes (if viable without introns).
  2. Extract mRNA, convert to cDNA, then use DNA polymerase.
  3. Artificial synthesis with a DNA synthesizer.
• Choose the method based on the feasibility and goal (e.g., presence of introns).