Question

Which of the following statements is FALSE?

A) In T-loop formation, the overhang region of the G-T strand invades repetitive sequences of telomere and forms a D-loop structure which is limited to the site of the strand invasion.
B) TRF2 protein plays a key role in forming the T-loop.
C) Human T-loops range from 5 to 10 thousand base pairs in length.
D) STN1 serves to limit digestion of the C-A strand (5-end).
E) STN1 degrades the 5-end of the chromosome (C-A strand). This helps produce the overhang of the 3-end of the DNA.

Answer 1

The false statement is that STN1 degrades the 5-end of the chromosome; in reality, STN1 protects telomeres. Telomeres consist of a six base-pair sequence, TTAGGG, and telomerase helps maintain their length which is crucial in stem cells and cancer cells. The correct option is E.

Step-by-step explanation:

The statement that is FALSE among those presented is E) STN1 degrades the 5-end of the chromosome (C-A strand). This helps produce the overhang of the 3-end of the DNA. STN1 is actually involved in protecting the telomeres and limiting unwanted degradation, not in degrading the 5-end of the chromosome.

Telomeres are repetitive sequences at the ends of linear chromosomes and do not code for any particular gene. They prevent the loss of genetic information during cell division by protecting the coding DNA. In human cells, telomeres consist of a six base-pair sequence, TTAGGG, repeated hundreds to thousands of times.

The enzyme telomerase is crucial for maintaining the length of telomeres, especially in cells that divide frequently, like stem cells, and in many cancer cells. Telomerase has an RNA template that allows it to add telomeric repeats to the 3' end of chromosomes, compensating for the shortening that occurs during DNA replication.

This is particularly important because the DNA polymerase can only add nucleotides to the 3' end, and without telomerase, chromosomes would progressively lose sequences with each round of cell division, potentially leading to cellular aging or apoptosis. The correct option is E.