Question
Question: The cos ends of DNA of lambda phage has nucleotides A. Five B. Ten C. Twelve D. Fifteen...
The cos ends of DNA of lambda phage has nucleotides
A. Five
B. Ten
C. Twelve
D. Fifteen
Solution
A bacterial virus or bacteriophage infecting Escherichia coli ( E. coli) bacteria is Enterobacteria phage λ (lambda phage, coliphage λ, officially Escherichia Lambda virus). In 1950, Esther Lederberg discovered it.
Complete Answer:
- The wild form of this virus has a temperate life cycle that allows it to either live inside the genome of its host through lysogeny or enter a lytic phase during which the cell is killed and lysed to produce offspring.
- Lambda strains, mutated at particular locations, are unable to lysogenized cells; instead, after superinfection of an already lysogenized cell, they expand and join the lytic cycle.
- A head (also known as a capsid), a tail, and tail fibres make up the phage particle. The head comprises the double-strand linear DNA genome of a phage. The phage particle recognises and binds to its host, E, during infection. Coli, allowing DNA to be expelled through the tail into the cytoplasm of the bacterial cell in the head of the phage.
- A "lytic loop" normally ensues, where the lambda DNA is repeated and new phage particles are produced within the cell.
- With more than 1000 protein molecules in total and one DNA molecule located in the phage head, the entire particle consists of 12-14 different proteins. It is still not entirely clear, however, whether the L and M proteins are part of the virion.
- All characterised lambdoid phages have an antitermination mechanism of N protein-mediated transcription, except for phage HK0222.
- 48,490 double-stranded, linear DNA base pairs are found in the genome, with single-strand 12-base segments at both ends of 5 '. The "sticky ends" of what is known as the cos site are these two single-stranded segments.
- In the host cytoplasm, the cos region circularises the DNA. The phage genome, therefore, is 48,502 base pairs in length in its circular form. It is possible to insert the lambda genome into the E.
- A chromosome of coli is then called a prophage. The cos site is the DNA area at which a single-stranded sticky end consists of the lambda genome that forms a base pair to give rise to a circular DNA as it reaches the bacterial cell. There are 12 bases in the lambda phage, hence 12 nucleotides at the end of the cos.
The correct Answer is option (C) Twelve.
Note: Linear Lambda DNA cos-ends are the product of a cut by the enzyme terminase. This enzyme is encoded by Lambda itself and, during the replication of phage DNA, behaves like a restriction enzyme. It is a cos-site-specific endonuclease in multimeric phage DNA. The ends of the resulting monomeric DNA (called cos-ends) are similar to those of common restriction enzymes formed by sticky (or cohesive) ends.Cos ends are much more sticky than the cohesive ends produced by restriction enzymes that usually have an overhang of 4 or 2 nucleotides because they have long 5 'overhangs (12 nucleotides). They are compatible for successful ligation because cos ends have complementary overhangs.