Eukaryotic DNA Replication - Termination

Question 1

How do telomeres come about?

Answer 1

The gap where the primer sequence was removed at the end of the lagging strand at the end of the chromosome cannot be filled by DNA polymerase because there is no available 3’ hydroxyl group for it to bind so another enzyme needs to come in to fill that space with DNA in order to prevent loss of genetic information.

Question 2

What enzymes produces and maintains telomeres?

Answer 2

Human telomerase enzyme

Question 3

What are the core components of a telomerase?

Answer 3

TERC is the RNA template that TERT uses to elongate the 3’ overhang on the lagging strand and create telomeric DNA repeats.

Question 4

Step 1 - telomere synthesis

Answer 4

TERT binds the existing telomeric sequence on the parent strand.

Question 5

Step 2 - telomere synthesis

Answer 5

Using TERC, TERT elongates the telomere of the parent strand.

Question 6

Step 3 - telomere synthesis

Answer 6

DNA polymerase alpha’s primase unit adds an RNA primer to and then extends to finish the rest of the lagging strand’s DNA.

Question 7

What cells are telomerases expressed in regarding mammals?

Answer 7

Stem cells

Question 8

What cells are telomerases not expressed in regarding mammals and why?

Answer 8

Telomerases are not expressed in somatic cells because they could turn them cancerous.

Question 9

Why are telomeres described as a mitotic clock?

Answer 9

It is a measure for how many times a cell has divided and gives a cell a defined time line.

Question 10

Telomeres become shorter until they are unable to be capped. Why does this happen and what is the consequence?

Answer 10

This happens because telomerase activity decreases with. The result is chromosomal instability which leads to cell death.