Chapter 8 Flashcards
dna replication is?
semi conservative
when does dna replication occur for eukaryotes?
it occurs during the S phase of the cell cycle(dna synthesis)
chromosome for prokaryotes vs eukaryotes
prokaryotes: one circular chromosome
eukaryotes: several linear chromosomes
where does replication begin?
special sites along the dna called the ORIGIN OF REPLICATION
replication occurs …?
bidirectionally
origin of replication in prokaryotes vs eukaryotes?
prokaryotes: one origin of replication
eukaryotes: multiple origins of replication
proteins recognize the “ori” aka origin of replication and then…?
bind to the dna and start unwinding it forming a replication bubble ( the structure that forms during dna replication when the double helix unwinds at the ori )
what is at the end of each replication bubble?
the replication fork: y shaped structure that progresses as replication occurs, it moves along the dna as more of the double helix unwinds.
what is helicase?
helicase is an enzyme that plays a role to unwind and separate the two strands by breaking the hydrogen bonds between the nitrogenous bases.
- binds at the replication fork
what are other proteins involved in replication?
single stranded dna binding proteins: bind to single stranded dna and keep strands separated
topoisomerases: helps relieve the torisonal stress and bind to dna
what does the enzyme dna polymerase do? give e.coli information
dna polymerase is an enzyme that catalyzes dna synthesis.
e coli: dna polymerase iii primary enzyme of replication at the replication fork
what direction do dna polymerase synthesis dna in?
5’ to 3’ direction
no known dna polymerase can…?
synthesize dna de novo
dna polymerase requires?
a free 3’ -OH group
what is the substrate that the dna polymerase uses?
dNTPS: deoxynucleotide triphosphate: consists of sugar, nitrogenous base, and 3 phosphate groups.
so what happens when dntp is available?
it binds to the dna polymerase. the enzyme then checks the base of the incoming dntp against the base on the template strand. if the template is a it will pair with t from the dntp. etc. this allows the dna polymerase to catalyze the formation of a new phosphodiester bond.
summary of dna polymerase/dntp?
dna polymerase helps ensure that the new dna strand is an accurate copy of the template by matching each incoming dntp to its complementary base on the template strand.
what are the 3 things needed in order for dna polymerase to synthesize a complementary strand of dna?
- a template that directs the synthesis of complementary dna strand.
- a primer to which nucleotides can be added to.
- dntps
what is a primer?
the primer is a short piece of rna that is made by enzyme called PRIMASE
as chains are elongating, one is being replicated in a continuous manner?
leading strand: one priming event
the other chain is being replicated in a discontinuous manner?
lagging strand: multiple priming events
what are the segments of dna that make up the lagging strand called?
okazaki fragments
what about the primer in the lagging strand?
it is removed by a different dna polymerase: dna polymerase i
- it is then replaced with deoxynucleotides
what about the gaps between the okazaki fragments?
they are sealed by an enzyme called DNA LIGASE
