Many repair proteins are isolated  like

(a) DNA methyl transferase
(b) DNA glycosylase
(c) DNA polymerase IV

Which one of the following represents the correct combination?
(1) (i)-(a), (ii)-(b), (iii)-(c)
(2) (i)- (b), (ii)-(c), (iii)-(a)
(3) (i)-(c), (ii)-(a), (iii)-(b)
(4) (i)-(c), (ii)-(b), (iii)-(a)

DNA Damage Responses: Damage Bypass, Damage Reversal, and Damage Removal with Key Repair Proteins

Cells face constant threats to their DNA integrity from various damaging agents. To maintain genomic stability, organisms have evolved complex DNA damage response systems that broadly fall into three main categories:

1. Damage Bypass

2. Damage Reversal

3. Damage Removal

Each category involves specialized proteins and enzymes that recognize, process, and repair DNA lesions. Understanding the correct association between damage types and repair proteins is critical for grasping cellular DNA repair mechanisms.

Categories of DNA Damage Responses and Corresponding Proteins

• (i) Damage Bypass:
  This mechanism allows DNA replication to continue past DNA lesions without immediately repairing them, often at the cost of increased mutation rates. Specialized DNA polymerases, called translesion synthesis (TLS) polymerases, perform this function by inserting nucleotides opposite damaged bases.

  • Example Protein: DNA polymerase IV (a TLS polymerase in prokaryotes) facilitates damage bypass.

• (ii) Damage Reversal:
  This pathway directly reverses DNA damage without excision or replacement. It restores the original DNA structure by enzymatic modification of the damaged base or lesion.

  • Example Protein: DNA methyltransferase reverses alkylation damage by transferring methyl groups from DNA bases to itself, restoring the original base.

• (iii) Damage Removal:
  This involves excision repair pathways where damaged bases or nucleotides are removed and replaced by newly synthesized DNA.

  • Example Protein: DNA glycosylase initiates base excision repair by recognizing and removing damaged bases, creating abasic sites for further processing.

Matching Proteins to Damage Responses

Analysis of the Given Options

• Option (1): (i)-(a), (ii)-(b), (iii)-(c)

  • Assigns DNA methyltransferase to damage bypass, which is incorrect.

  • Assigns DNA glycosylase to damage reversal, which is incorrect.

  • Assigns DNA polymerase IV to damage removal, which is incorrect.

• Option (2): (i)-(b), (ii)-(c), (iii)-(a)

  • DNA glycosylase as damage bypass? Incorrect.

  • DNA polymerase IV as damage reversal? Incorrect.

  • DNA methyltransferase as damage removal? Incorrect.

• Option (3): (i)-(c), (ii)-(a), (iii)-(b)

  • DNA polymerase IV as damage bypass? Correct.

  • DNA methyltransferase as damage reversal? Correct.

  • DNA glycosylase as damage removal? Correct.

• Option (4): (i)-(c), (ii)-(b), (iii)-(a)

  • DNA polymerase IV as damage bypass? Correct.

  • DNA glycosylase as damage reversal? Incorrect.

  • DNA methyltransferase as damage removal? Incorrect.

Correct Answer

Option (3): (i)-(c), (ii)-(a), (iii)-(b)

Related Keywords for SEO Optimization

• DNA damage bypass

• DNA damage reversal mechanisms

• DNA damage removal pathways

• DNA polymerase IV translesion synthesis

• DNA methyltransferase repair

• DNA glycosylase base excision repair

• DNA repair proteins

• DNA damage response categories

• Prokaryotic DNA repair

• Base excision repair enzymes

• Direct repair mechanisms

• Translesion DNA synthesis polymerases

Conclusion

The complex DNA damage responses in cells are categorized as:

• Damage Bypass (i): Performed by DNA polymerase IV, allowing replication past lesions.

• Damage Reversal (ii): Carried out by DNA methyltransferase, directly restoring damaged bases.

• Damage Removal (iii): Initiated by DNA glycosylase, removing damaged bases for repair.

Thus, the correct combination is option (3): (i)-(c), (ii)-(a), (iii)-(b). This understanding is fundamental to appreciating how cells maintain genomic stability in the face of diverse DNA damage.