DNA replication Flashcards
What is helicase?
It unwinds parental double helix at replication forks
What is a single-strand binding portein
It binds to and stabilizes the single stranded DNA until it is used as a template
What is topoisomerase
it relieves overwinding strain ahead of replication forks by breaking, swiveling, and rejoining DNA
prevent supercoiling
what is primase
it synthesizes an RNA primer at the 5’ end of the leading strand and at the 5’ end of each Okazaki fragment of the lagging strand
What does DNA pol III do
it synthesizes a new DNA strand by adding nucleotides to an RNA primer
what does DNA pol I do
it removes the RNA nucleotides from the primer at the 5’ and replaces then with DNA nucleotides
What is DNA ligase
it joins okazaki fragments on the lagging strand
it joins the 3’ of DNA that replaces primer to rest of leading strand
What are Okazaki fragments
short sections of DNA that are synthesized on the lagging strand of the replicating DNA
What is the replication fork
the open section of DNA where DNA pol III can replicate the parent strand
What is DNA pol
an enzyme that replicates DNA
what is the leading strand
the new DNA strand that continiously grows in the 5’-3’ direction
it requires one primer
features of leading strand
one primer needed
daughter strand elongates towards the replication fork
made continuously
synthesized in 5’-3’
features of lagging strand
made in segments
daughter strand elongates away from the replication fork
multiple primers are needed
synthesized in the 5’-3’ direction
How does the lagging strand get analyzed and fused?
- DNA pol III binds to 3’ end of RNA primer
- DNA pol synthesizes in 5’-3’ direction until it reaches the previous RNA primer
- DNA pol III falls off and is replaces by pol I
- pol I removes each RNA nucleotide on primer and replaces with DNA
Step 2: DNA pol III falls off and is replaced by DNA pol I. - when it reaches the 5’ end of next fragment, it falls off and DNA ligase closes the gap between the two
What provides energy for the addition of a new nucelotide?
Release of pyrophosphate from the incoming nucleotide, and then hydrolysis of the pyrophosphate to inorganic phosphate
what is the semi conservative model of replication
two identical DNA double helices are formed from replication, each with one parent strand and one daughter strand
what are the three requirements of replication
parental DNA molecule, Enzymes, Nucleotide triphosphates
what is the difference in origin of replication for bacteria and eukaryotes?
bacteria have single origins of replication while eukaryotes have many
what direction does replication occur from the origin
both directions until entire molecule is copied
what can DNA polymerase not do?
initiaite synthesis, it can only add to an existing 3’OH end
What is the purpose of RNA primase
it can start an RNA chain from scratch and provide a 3’OH starting point for the DNA pol
what does DNA pol III do
synthesizes a new DNA strand by covalently adding nucleotides to the 3’ end of a pre-existing DNA strand or DNA primer
what does DNA Pol I do
It removes RNA nucelotides of a primer from the 5’ end and replaces them with DNA nucleotides
What are the 3 common features of DNA pol
Add new bases to 3’ end of strands
synthesize in 5’3’ direction
require and RNA primer
How is energy provided for nucleotide additions
dATP supplies adenine to DNA and as each monomer is added, it loses two phosphate groups as a molecule of pyrophosphate
Centromere
the constricted waist of chromosomes where kinetochores assemble
What are kinetochores?
Protein complexes that assemble at centromeres of chromosomes
they serve as attachment sites for microtubules in cell division
What is cohesion in chromosomes?
proteins that join sister chromatids together during mitosis.
The cleavage of this triggers anaphase
Before replication, each chromosome is composed of:
a single DNA molecule
What does DNA ligase do specifically
it makes the final phosphodiester bond at each “nick” between the 3’-OH of the DNA replacement nucleotides (DNA pol I removed primer) and the 5’ end of the DNA pol III strand
Which phase is a cell in most of the time?
interphase
after replication, each chromosome is composed of
2 identical DNA molecules
What are the replicated chomosomes called and how are they held together?
They are called sister chromatids and are held together at their centromeres by cohesion proteins.
