Final answer:
T4 and Lambda bacteriophages overcome the challenge of packaging linear double-stranded DNA into small viral particles by forming circular DNA molecules within the host cell. T4 phage DNA circularizes through the action of DNA ligase, while Lambda phage has cohesive ends that anneal. These characteristics are advantageous for their replication and for genetic engineering applications.
Step-by-step explanation:
Bacteriophages such as T4 and Lambda possess linear double-stranded DNA that must be efficiently packaged within their small capsids. T4 solves the issue by attaching its linear DNA ends together, forming a circular molecule once inside the host cell. This is important for replication as the circular DNA allows the use of bacterial host mechanisms to properly copy the phage genome. The process requires the enzyme DNA ligase, and in the absence of a functional enzyme, as found in some T4 mutants, DNA replication is hindered, leading to slower growth rates and accumulation of short DNA fragments known as Okazaki fragments.
Lambda phage, on the other hand, has linear DNA with single-stranded complementary 'cohesive ends' which anneal to form a circular molecule inside the host. This circularization allows Lambda to enter either a lytic cycle, where it will replicate and burst the cell, or a lysogenic cycle, integrating into the host genome and replicating along with it.
The advantages of using both phages are evident in their application in genetic engineering and biotechnology, such as constructing genomic libraries with large DNA inserts. Compared to plasmids, phages like Lambda can accept larger fragments of DNA, making them highly efficient for cloning and representing complex genomes.