Q.Name any two natural cloning vectors. Give reasons that make them act as cloning vectors. Write the two characteristics the engineered vectors are made to possess.
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Start your 14-day free trial to unlock the full solution →Plasmids and bacteriophages are natural cloning vectors due to their self-replicating nature and ability to transfer DNA; engineered vectors are designed with an origin of replication and a selectable marker for efficient cloning.
A cloning vector is essentially a DNA molecule that can carry foreign genetic material into a host cell, where it can be replicated and expressed. Think of it as a delivery vehicle for genes. For a molecule to serve as an effective cloning vector, it must possess certain fundamental properties that allow it to be introduced into a host, replicate independently, and carry the desired foreign DNA. Natural elements like plasmids and bacteriophages inherently possess these properties, making them excellent starting points for genetic engineering.
Natural Cloning Vectors and Their Reasons
Two prominent natural cloning vectors are plasmids and bacteriophages.
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Plasmids
Plasmids are small, circular, double-stranded DNA molecules found naturally in bacteria, separate from the bacterial chromosome.
- Reasons they act as cloning vectors:
- Self-replication: Plasmids possess their own origin of replication (ori), allowing them to replicate independently within the host cell, separate from the host's chromosomal DNA. This ensures that any foreign DNA inserted into the plasmid is also replicated.
- Small size: Their relatively small size makes them easy to isolate from bacterial cells and manipulate in the laboratory.
- Non-essential genes: The genes carried on plasmids are often non-essential for the host's survival under normal conditions, meaning their manipulation or insertion of foreign DNA usually doesn't harm the host.
- Transferability: Some plasmids can be transferred between bacterial cells through conjugation, which can be advantageous for spreading recombinant DNA.
- Ability to carry foreign DNA: They can be cut open with restriction enzymes, allowing foreign DNA fragments to be inserted and ligated into them.
- Reasons they act as cloning vectors:
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Bacteriophages
Bacteriophages are viruses that infect bacteria. They inject their genetic material into the host bacterium, where it can replicate.
- Reasons they act as cloning vectors:
- Efficient DNA delivery: Bacteriophages have a natural, highly efficient mechanism for injecting their DNA into bacterial cells, making them excellent at delivering foreign DNA.
- Accommodation of larger DNA inserts: Compared to typical plasmids, some bacteriophages (like lambda phage) can accommodate larger fragments of foreign DNA, which is useful for cloning larger genes or gene clusters.
- Replication within host: Once inside the host, the phage DNA replicates using the host's machinery, ensuring the replication of the inserted foreign DNA.
- Lytic or Lysogenic cycles: Depending on the phage, they can either undergo a lytic cycle (leading to cell lysis and release of many new phages) or a lysogenic cycle (integrating their DNA into the host chromosome), offering different strategies for cloning and gene expression.
- Reasons they act as cloning vectors:
Characteristics of Engineered Vectors
While natural plasmids and phages are useful, they are often modified or "engineered" to enhance their utility as cloning vectors. This engineering makes them more efficient, easier to use, and allows for selection of successful cloning events.
Two characteristics that engineered vectors are made to possess are:
- Origin of Replication (ori) …
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