The end-replication problem states that small stretches of DNA at the 3′ ends of chromosomes cannot be copied because these stretches are not covered by Okazaki fragments . Because of the end-replication problem, chromosome ends are slowly shortened over time.
Which ends could not be replicated by DNA polymerase?
The ends labeled B and C could not be replicated by DNA polymerase. DNA polymerase makes a strand in the 5 to 3 direction using a template strand that is running in the 3 to 5 direction.
Which strand Cannot be replicated all the way to the end?
The end replication problem hypothesis proposes that the ends of linear DNA cannot be replicated completely during lagging strand DNA synthesis . Although the idea has been widely accepted for explaining telomere attrition during cell proliferation, it has never been directly demonstrated.
What happens to the lagging strand at the end of a chromosome?
On the lagging strand, DNA is synthesized in short stretches , each of which is initiated by a separate primer. When the replication fork reaches the end of the linear chromosome, there is no place for a primer to be made for the DNA fragment to be copied at the end of the chromosome.
Which strand can be continuously replicated?
The leading strand is synthesized continuously, whereas the lagging strand is synthesized in short pieces termed Okazaki fragments.
Why can nucleotides only be added to the 3 end?
DNA polymerase will add the free DNA nucleotides using complementary base pairing (A-T and C-G) to the 3′ end of the primer this will allow the new DNA strand to form. ... Nucleotides cannot be added to the phosphate (5′) end because DNA polymerase can only add DNA nucleotides in a 5′ to 3′ direction.
Is RNA synthesized 5 to 3?
An RNA strand is synthesized in the 5′ → 3′ direction from a locally single stranded region of DNA.
Why is DNA only synthesized from 5 to 3?
Because the original strands of DNA are antiparallel , and only one continuous new strand can be synthesised at the 3′ end of the leading strand due to the intrinsic 5′-3′ polarity of DNA polymerases, the other strand must grow discontinuously in the opposite direction.
WHO removes RNA primer?
In prokaryotic cells, polymerase III is the major replicative polymerase, functioning in the synthesis both of the leading strand of DNA and of Okazaki fragments by the extension of RNA primers. Polymerase I then removes RNA primers and fills the gaps between Okazaki fragments.
Why does DNA replication occur in the 5 ‘- 3 direction only?
DNA is always synthesized in the 5′-to-3′ direction, meaning that nucleotides are added only to the 3′ end of the growing strand . ... (B) During DNA replication, the 3′-OH group of the last nucleotide on the new strand attacks the 5′-phosphate group of the incoming dNTP. Two phosphates are cleaved off.
Which is the lagging strand?
The lagging strand is the DNA strand replicated in the 3′ to 5′ direction during DNA replication from a template strand . It is synthesized in fragments. ... The discontinuous replication results in several short segments which are called Okazaki fragments.
What happens if mutations are not corrected?
Most mistakes are corrected, but if they are not, they may result in a mutation defined as a permanent change in the DNA sequence . Mutations can be of many types, such as substitution, deletion, insertion, and translocation. Mutations in repair genes may lead to serious consequences such as cancer.
What is the end replication paradox?
The end-replication problem
The DNA at the very end of the chromosome cannot be fully copied in each round of replication , resulting in a slow, gradual shortening of the chromosome.
Is the leading strand 5 to 3?
One of these is called the leading strand, and it runs in the 3′ to 5′ direction and is replicated continuously because DNA polymerase works antiparallel, building in the 5′ to 3′ direction. ... The fragments are bound together by the enzyme DNA ligase in order to complete replication in the lagging strand of DNA.
What are the 4 steps of replication?
- Step 1: Replication Fork Formation. Before DNA can be replicated, the double stranded molecule must be “unzipped” into two single strands.
- Step 2: Primer Binding. The leading strand is the simplest to replicate.
- Step 3: Elongation.
- Step 4: Termination.
Is RNA primer needed for leading strand?
On the leading strand, only a single RNA primer is needed , and DNA is synthesized continuously, whereas on the lagging strand, DNA is synthesized in short stretches, each of which must start with its own RNA primer.
