Question

Dna repair mechanism biology discussion

Answer 1

Repair Mechanism # 1. Photo Reactivation:

We know that exposure of UV-irradiated bacteria immediately afterwards to visible light restores to a considerable degree the viability of the UV-inactivated bacteria. This phenomenon mown as photo reactivation, is based on enzymatic cleavage of the thymine dimers.

The enzyme, photolyase, binds to the thymine dimer and catalyses photochemical cleavage of the cyclobutane ring of the dimer to make the thymine’s free. The enzyme uses visible light for the reaction. Besides thymine-dimers, other pyrimidine-dimers—like cytosine-cytosine and cytosine-thymine dimer—are also attacked by the enzyme. The enzyme is devoid of any species-specificity. Photolyases have been detected in both prokaryotes and eukaryotes

Answer 2

DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome.]In human cells, both normal metabolicactivities and environmental factors such as radiation can cause DNA damage, resulting in as many as 1 million individual molecular lesions per cell per day.  Many of these lesions cause structural damage to the DNA molecule and can alter or eliminate the cell's ability to transcribe the gene that the affected DNA encodes. Other lesions induce potentially harmful mutations in the cell's genome, which affect the survival of its daughter cells after it undergoes mitosis. As a consequence, the DNA repair process is constantly active as it responds to damage in the DNA structure. When normal repair processes fail, and when cellular apoptosisdoes not occur, irreparable DNA damage may occur, including double-strand breaks and DNA crosslinkages (interstrand crosslinks or ICLs).] This can eventually lead to malignant tumors, or cancer as per the two hit hypothesis.

The rate of DNA repair is dependent on many factors, including the cell type, the age of the cell, and the extracellular environment. A cell that has accumulated a large amount of DNA damage, or one that no longer effectively repairs damage incurred to its DNA, can enter one of three possible states:

an irreversible state of dormancy, known as senescence

cell suicide, also known as apoptosis or programmed cell death

unregulated cell division, which can lead to the formation of a tumor that is cancerous

The DNA repair ability of a cell is vital to the integrity of its genome and thus to the normal functionality of that organism. Many genes that were initially shown to influence life spanhave turned out to be involved in DNA damage repair and protection