Table of Contents
Do nucleotides get added to the 3 or 5 end?
DNA is always synthesized in the 5′-to-3′ direction, meaning that nucleotides are added only to the 3′ end of the growing strand. As shown in Figure 2, the 5′-phosphate group of the new nucleotide binds to the 3′-OH group of the last nucleotide of the growing strand.
Why can’t DNA polymerase add nucleotides to the 5 end?
DNA pol uses the energy provided by hydrolysis of the high-energy phosphate bond at the 5′ end of the incoming nucleotide to add it to the 3′ end of the growing DNA. Without the high-energy phosphate bond, the correct nucleotide can not be added.
What end can nucleotides be added to?
3′ end
DNA polymerases can only add nucleotides to the 3′ end of an existing DNA strand. (They use the free -OH group found at the 3′ end as a “hook,” adding a nucleotide to this group in the polymerization reaction.)
Why does DNA replication only occur in the 5 to 3 direction?
DNA replication only occurs in the 5′ to 3′ direction because DNA polymerase requires a free 3′ hydroxyl group to attach the new nucleotide to.
Why can you only add to the 3 end?
The DNA is only copied in the 5′ to 3′ direction because eukaryotic chromosomes have many origins for each chromosome in keeping with their much larger size. If some were copied in the other direction, mistakes will happen. It keeps every cell division on the same page, so to speak.
What adds nucleotides to the 3 end of the DNA?
DNA polymerase
During elongation, an enzyme called DNA polymerase adds DNA nucleotides to the 3′ end of the newly synthesized polynucleotide strand.
How are new nucleotides added to the chain?
RNA Polymerase II (RNA Pol II) is the enzyme that adds nucleotides to a new DNA chain produced during transcription. As it moves along, it links nucleotides into a new chain by matching the free floating nucleotides with their corresponding base-pairs on the template strand of DNA.
Why does DNA replication start at 5 ends?
DNA replication occurs in the 5′ to 3′ direction. DNA polymerase can only add nucleotides to the 3′ OH group of the growing DNA strand, this is why DNA replication occurs only in the 5′ to 3′ direction.
Why can nucleotides not be added to the phosphate end of DNA?
Nucleotides cannot be added to the phosphate (5’) end because DNA polymerase can only add DNA nucleotides in a 5’ to 3’ direction. The lagging strand is therefore synthesised in fragments.
Can DNA polymerase add nucleotides to the deoxyribose strand?
DNA polymerase adds nucleotides to the deoxyribose (3’) ended strand in a 5’ to 3’ direction. Lagging strand is synthesised in fragments. Nucleotides cannot be added to the phosphate (5’) end because DNA polymerase can only add DNA nucleotides in a 5’ to 3’ direction.
What happens if one or more nucleotides are missing from a strand?
If one or more nucleotide is missing in one strand, repair of the missing nucleotide would be impossible for 3′ to 5′ synthesis, because no 5′-triphosphate is present. On the other hand, 5′ to 3′ synthesis does not require a 3′-triphosphate present at the repair site. This is important.
What happens if there is no proofreading of a nucleotide?
If an error occurred, proofreading would remove the newly incorporated nucleotide at the 5′ end along with the high-energy phosphate bond. Without the high-energy phosphate bond, the correct nucleotide can not be added. Without proofreading, life wouldn’t be good. Hope this makes sense.