chromosome replication occurs via dna synthesis in eukaryotic cell during g1 phase.
during what phase does chromosome replication occur via dna synthesis in eukaryotic cell?
g1 phase
eukaryotic dna ligase 1 catalyzes a reaction that is chemically universal to all ligases. dna ligase 1 utilizes adenosine triphosphate (atp) to catalyze the energetically favorable ligation events in both dna replication and repair. during the synthesis phase (s-phase) of the eukaryotic cell cycle, dna replication occurs. dna ligase 1 is responsible for joining okazaki fragments formed during discontinuous dna synthesis on the dna’s lagging strand after dna polymerase δ has replaced the rna primer nucleotides with dna nucleotides. if the okazaki fragments are not properly ligated together, the unligated dna (containing a ‘nick’) could easily degrade to a double strand break, a phenomenon known to cause genetic mutations. in order to ligate these fragments together, the ligase progresses through three steps:
lig1
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