Question

A problem known as the end-replication problem (telomere problem) exists in eukaryotic chromosomes wherein the chromosomes shorten with each round of DNA replication. Select the statements that best explain why the end-replication problem exists in eukaryotic chromosomes​ (select all statements that apply)
1)​ The RNA primer is removed in a 3' to 5' direction
2) DNA polymerase requires a primer for DNA synthesis
3) ​DNA ligase links the 5' OH group of one fragment to the 3' phosphate group of an adjacent fragment
4) The lagging strand is synthesized from the 3' end to the 5' end
5) DNA polymerase synthesizes DNA from the phosphate end to the hydroxyl end

Answer 1

2) and 5) are correct

Explanation:

• Telomere represents linear ends of eukaryotic chromosome and consists of repeated nucleotides, protects terminal end of chromosomes from exonucleases and other damaging chemicals and also maintain divisional capacity of cells
• Telomerase is a ribonucleoprotein complex consisting of RNA and several proteins, where RNA component of telomerase act as template and protein component has reverse transcriptase activity that synthesize DNA using RNA as a template
• Telomerase only extends 3' end of parental strand
• Extension and translocation repeats several times
• At telomeric region 3' end of one end is over-hanged on 5' end of another strand
• Over-hanged 3' end create a loop called T loop which mask the end of DNA strand          

Answer 2

Answer:

2 and 5

Explanation:

DNA replication occurs in S phase of cell cycle, is the process of DNA duplication in which one molecule of DNA is copied into two molecules. DNA is replicated by DNA polymerase enzyme which requires primer for initiation of replication. In leading strand, only one primer is required at the time of initiation, but for lagging strand, lots of primers are required, one at each okazaki fragment.

Telomere become short at each cell division because DNA polymerase requires a primer for DNA synthesis  and DNA polymerase synthesizes DNA from the phosphate end to the hydroxyl end both the conditions are not filled at the telomeres.