Question

The structure of the bacterial chromosome remains the same during bacterial cell growth. Do you agree? Explain

Answer 1

                                

                                           A circular chromosome is a chromosome in bacteria, archea, mitochondria and chloroplasts, in the form of a molecule of circular DNA , unlike the linear chromosome of most eukaryotes. Most prokaryotic chromosomes contain circular DNA molecule having no free ends. However a circular chromosome can provide other challenges for celss. After replication, two progeny circular circular chromosomes can sometimes remain interlinked or tangled, and they must be resolved so that each cell inherits one complete copy of the chromosome during cell division

                                        Chromosomal replication proceeds in three major stages

• Initiation
• Elongation
• Termination

                                   The initiation stage starts with the ordered assembly of "initiator" proteins at the origin region of the chromosome called oriC. These assembly stages are regulated to ensure that chromosome replication occurs only once in each life cycle.

                                   During elongation phase of replication, the enzymes that were assembled at oriC proceed in opposite directions away from the oriC replicating DNA to create two identical copies. This process is known as bidirectional replication.

                                  The entire assembly of molecules involved in DNA replication on each arm is called a replisome. At the forefront of the replisome is a DNA helicase that unwinds the two strands of DNA , creating a moving "replication fork". The two unwound single strands of DNA serve as templates for DNA polymerase, which moves with the helicase to synthesise a complementary copy of each strand . In this way, two identical copies of the original DNA are created . At last when elongation enzymes disassemble, and the two "daughter " chromosomes are resolved before cell division is completed.

               Hence the structure of bacterial chromosome remains same during bacterial cell growth.