Question

Why are DNA proofreading enzymes necessary? A DNA molecule can be thought of as having 2 components, corresponding to the sides and rungs of a ladder. What are these 2 components? What class of molecule is telomerase? What does telomerase do? In which human cells is telomerase appropriately active? In what kinds of cells is telomerase inappropriately active?

Answer 1

Why are DNA proofreading enzymes necessary?

Although DNA polymerase is a highly accurate enzyme, there are often eroors that it makes while synthesising new DNA molecules. There errors need to be rectified in order to preserve the integrity of the DNA sequence because incorrect bases can often lead to serious consequences due to mutations. The consequences of such errors can also become inheritable if they occur in the reproductive germ cells, thereby causing genetic diseases.

Most DNA polymerase enzymes have an inherent proofreading activity that corrects the errors while DNA replication. However, a fraction of these errors often remain undetected. There comes the role of DNA repair system which corrects the errors after replication. There are two main types of repair system: Mismatch repair and Base excision repair.

A DNA molecule can be thought of as having 2 components, corresponding to the sides and rungs of a ladder. What are these 2 components?

The DNA backbone made up of ribose sugar and phosphate groups correspond to the sides of the ladder

The nucleotide bases (adenine, guanine, cytosine, thymine) correspong to the rungs of the ladder

What class of molecule is telomerase?

Telomerase belongs to the Reverse Transcriptase class of enzymes.

What does telomerase do?

Telomerase are specialized to synthesize single-stranded DNA using a single-stranded RNA as the template. Telomerase adds species-specific telomerase repeat sequence at the end of chromosomes at the telomere regions, thereby ensuring that the chromosomes do not keep shortening with each cycle of DNA replication.

In which human cells is telomerase appropriately active?

Telomerase is appropriately active in gametes (germ cells) and cancerous cells.

In what kinds of cells is telomerase inappropriately active?

Telomerase is inappropriately active in the somatic cells.

_________________________________________

[Kindly give a thumbs up]