Edexcel iGCSE Biology-6.12-6.13 The Process of Genetic Modification- Study Notes- New Syllabus
Edexcel iGCSE Biology-6.12-6.13 The Process of Genetic Modification- Study Notes- New syllabus
Edexcel iGCSE Biology-6.12-6.13 The Process of Genetic Modification- Study Notes -Edexcel iGCSE Biology – per latest Syllabus.
Key Concepts:
6.12 understand how restriction enzymes are used to cut DNA at specific sites and ligase enzymes are used to join pieces of DNA together
6.13 understand how plasmids and viruses can act as vectors, which take up pieces of DNA, and then insert this recombinant DNA into other cells
Understanding Restriction Enzymes & Ligase Enzymes
🌱 Introduction
In genetic engineering, enzymes act as molecular tools to cut and join pieces of DNA precisely.
Two important types of enzymes used are:
- Restriction enzymes – for cutting DNA
- Ligase enzymes – for joining DNA fragments
These enzymes help scientists manipulate genes to form recombinant DNA – DNA made by combining genetic material from different sources.
✂️ Restriction Enzymes – “DNA Scissors” 
Definition:
Restriction enzymes (also called restriction endonucleases) are enzymes that cut DNA at specific sequences known as recognition sites.
- Each enzyme recognizes a specific short DNA sequence (usually 4-8 base pairs long).
- They cut DNA between specific bases, producing:
- Sticky ends → with overhanging unpaired bases
- Blunt ends → with no overhangs
- Example (conceptual): If the enzyme recognizes AATT, it cuts between these bases wherever it appears in the DNA.
Purpose:
– To cut out a desired gene from one organism’s DNA.
– To open a plasmid vector (circular DNA in bacteria) for inserting the gene.
🧩 Ligase Enzymes – “DNA Glue”
Definition:
Ligase enzymes are used to join DNA fragments together, forming a continuous DNA strand.
- DNA ligase seals the sugar-phosphate backbone between adjacent nucleotides.
- It joins the sticky ends (or blunt ends) of DNA fragments.
- Helps insert a foreign gene into a plasmid → forming recombinant DNA.
Purpose:
– To combine the cut gene with the plasmid vector.
– This recombinant plasmid can then be inserted into a host cell (like bacteria) for cloning or protein production.
⚙️ Simplified Process
| Step | Enzyme | Function | Result |
|---|---|---|---|
| 1 | Restriction enzyme | Cuts DNA at specific recognition sites | Desired gene isolated + plasmid opened |
| 2 | Ligase enzyme | Joins DNA fragments together | Recombinant DNA formed |
🧠 Mnemonic Trick
“R cuts, L links” → Restriction enzyme cuts, Ligase links the pieces.
💡 Example Use in Biotechnology
In the production of human insulin using bacteria:
- Restriction enzymes cut the human insulin gene and bacterial plasmid.
- Ligase joins them → recombinant plasmid formed.
- Plasmid inserted into bacteria → bacteria start producing insulin.
📋 Summary Table
| Enzyme Type | Function | Recognizes Specific Sites? | Produces Sticky/Blunt Ends? | Used For |
|---|---|---|---|---|
| Restriction enzyme | Cuts DNA | Yes | Sticky or Blunt | Isolating genes, opening plasmids |
| Ligase enzyme | Joins DNA | No | Joins ends | Forming recombinant DNA |
🧾 Quick Recap
Restriction enzymes → cut DNA at specific sites
Ligase enzymes → join DNA fragments
Together → make recombinant DNA
Used in genetic engineering (e.g., insulin production)
Memory tip: Restriction = Remove, Ligase = Link!
Understanding How Plasmids and Viruses Act as Vectors
🌱 Introduction
In genetic engineering, a vector is a carrier molecule that transfers foreign DNA (a desired gene) into another cell.
Common vectors used by scientists are:
- Plasmids (from bacteria)
- Viruses (genetic material surrounded by a protein coat)
Vectors help in creating genetically modified organisms (GMOs) by inserting useful genes into their cells.
🧫 What is a Vector?
Definition:
A vector is any DNA molecule that can carry a foreign gene and deliver it into a host cell for expression or replication.
- Role:
- To transport recombinant DNA into the target organism’s cell.
- Ensures the foreign gene becomes part of the host DNA or starts functioning inside it.
🧩 Plasmids as Vectors
What is a Plasmid?
- A small, circular DNA molecule found naturally in bacteria.
- It is separate from the bacterial chromosome.
- Can replicate independently inside bacterial cells.
Why Used as a Vector:
- Easily removed, modified, and reinserted into bacteria.
- Can carry foreign DNA (inserted using restriction and ligase enzymes).
Steps in Using Plasmids as Vectors:
- Isolation of Plasmid: The plasmid is removed from a bacterial cell.
- Cutting the Plasmid: Restriction enzymes cut open the plasmid at a specific site.
- Insertion of Foreign Gene: The desired gene (cut from another organism’s DNA) is joined to the plasmid using ligase enzyme → forming recombinant plasmid.
- Transfer to Host Cell: The recombinant plasmid is inserted back into a bacterial cell.
- Replication & Expression: The bacteria multiply → all copies contain the new gene → the gene gets expressed (e.g., to produce insulin).
🧠 Trick to Remember:
Plasmid = Portable DNA Circle (PDC) → small, circular, and portable for gene transfer.
🦠 Viruses as Vectors
What is a Virus?
- A tiny infectious agent made of DNA or RNA enclosed in a protein coat.
- Viruses can infect living cells and inject their genetic material inside them.
How They Work as Vectors:
- Scientists remove the harmful viral genes (that cause disease).
- A useful foreign gene is inserted into the viral DNA.
- The modified virus infects the target cell → injecting the recombinant DNA inside.
- The host cell’s machinery starts expressing the new gene.
Advantages of Viral Vectors:
- Very efficient at delivering DNA into host cells.
- Can target specific types of cells.
Example Use:
In gene therapy, viruses deliver healthy genes to replace faulty ones in human cells.
⚙️ Comparison Table
| Feature | Plasmid Vector | Virus Vector |
|---|---|---|
| Source | Bacteria | Viruses |
| Structure | Small circular DNA | DNA/RNA with protein coat |
| Function | Carries gene into bacterial cells | Delivers gene into host (animal/plant/human) cells |
| How DNA is Delivered | By transformation (uptake by bacteria) | By infection (virus injects DNA) |
| Example Use | Bacterial insulin production | Gene therapy or vaccine development |
| Advantage | Easy to handle in lab | Very efficient in gene transfer |
💡 Importance of Vectors
- Essential tools for recombinant DNA technology.
- Allow genes to be cloned, transferred, or expressed in different organisms.
- Used in medicine (insulin), agriculture (GM crops), and research (gene studies).
🧾 Quick Recap
Vector = DNA carrier for transferring genes.
Plasmid = small bacterial DNA circle; easy to modify & replicate.
Virus = injects DNA/RNA into cells; efficient gene delivery.
Restriction enzyme cuts → Ligase joins → Vector carries.
Used in gene therapy, insulin production, and GMOs.
Memory Tip: “Plasmids deliver in bacteria, Viruses deliver everywhere!”