#15. what is the end-replication problem? why, in the absence of telomerase, do the ends of the linear chromosomes get progressively shorter each time dna is replicated?

The DNA replication by the action of DNA polymerase takes place in the 3' to 5' direction on the leading strand. The lagging strand which has the opposite orientation or polarity as that of the leading strand requires a more time to get synthesised. The DNA replication of the lagging strand happens in short segments where a RNA primer forms a compliment with a part of the DNA segment on its 3' end. This RNA primer helps initiate the replication of the Okazaki fragments. When the replication on the lagging strand reaches its end, the RNA primer forms a compliment with the last bit of the strand. This small segment gets missed in the end as no more DNA is left to form a RNA primer-DNA compliment. Such shortening of the lagging strand in the replication process is the end-replication problem.

Telomeres are protective ends of the DNA strands. These ends contain a poly-A tail. When the lagging strand replication reaches its end, the RNA primer forms a compliment with the telomere and initiates the replication. This leads to the shortening of the telomere and not the coding segments on the lagging strand of DNA. The telomerase repairs the shortened telomere by re-synthesising it.

ecological efficiency: % of usable energy transferred as

biomass from one trophic level to the next typical is 10% efficient (90% of

energy is lost),is diagramed as the pyramid of energy flow. then osprey eagle

are tertiary consumer and the shrimp are primary consumer, so to balance

mass of shrimp (1/0.1) / 0.1 = 100 kg