chromosome replication occurs in eukaryotic cell asexually.
chromosome replication occurs in eukaryotic cell asexually.
when does chromosome replication occur in eukaryotic cell?
asexually
all living organisms are the products of repeated rounds of cell growth and division. during this process, known as the cell cycle, a cell duplicates its contents and then divides in two. the purpose of the cell cycle is to accurately duplicate each organism's dna and then divide the cell and its contents evenly between the two resulting cells. in eukaryotes, the cell cycle consists of four main stages: g, during which a cell is metabolically active and continuously grows; s phase, during which dna replication takes place; g, during which cell growth continues and the cell synthesizes various proteins in preparation for division; and the m (mitosis) phase, during which the duplicated chromosomes (known as the sister chromatids) separate into two daughter nuclei, and the cell divides into two daughter cells, each with a full copy of dna. compared to the eukaryotic cell cycle, the prokaryotic cell cycle (known as binary fission) is relatively simple and quick: the chromosome replicates from the origin of replication, a new membrane is assembled, and the cell wall forms a septum which divides the cell into two.
cell cycle checkpoint
the circular bacteria chromosome replication is best understood in the well-studied bacteria "escherichia coli" and "bacillus subtilis". chromosome replication proceeds in three major stages: initiation, elongation and 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 cell cycle. during the elongation phase of replication, the enzymes that were assembled at oric during initiation proceed along each arm ("replichore") of the chromosome, in opposite directions away from the oric, replicating the 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 (together with other proteins) to synthesise a complementary copy of each strand. in this way, two identical copies of the original dna are created. eventually, the two replication forks moving around the circular chromosome meet in a specific zone of the chromosome, approximately opposite oric, called the terminus region. the elongation enzymes then disassemble, and the two "daughter" chromosomes are resolved before cell division is completed.
circular prokaryote chromosome