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#DNA repair

68 public questions tagged with this topic.

ZOOLOGY

Which type of enzyme seals the DNA fragments after cutting?

DNA ligase joins the cut DNA fragments by forming phosphodiester bonds between them. This follows from latest NCERT 2026-27 principle explaining the concept clearly for NEET students in simple steps as per rationalized syllabus.

Ref: NCERT Biology Textbook - Latest Edition for Academic Session 2026-27 (Zoology section, Rationalized Textbook for Class XI and XII), Chapter: Biology - Zoology portion (Latest NCERT Textbooks for Academic Session 2026-27 - Rationalized Edition for Class XI and XII), Topic: Structural organization, ph

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Transgenic Plant -2

Repair of ZFN-induced breaks commonly occurs via:

Repair of nuclease induced breaks determines editing outcome and is governed by competitive engagement of canonical non-homologous end joining NHEJ and homology-directed repair HDR pathways. NHEJ active throughout cell cycle especially G1, initiated by Ku binding, DNA-PKcs activation, end processing by Artemis and polymerase mu, ligation by Lig4-XRCC4-XLF complex. It is error-prone with indels up to tens of base pairs at cleavage site leading to gene disruption valuable for knockout breeding. Alternative microhomology mediated end joining using Pol theta also produces deletions. HDR pathway re

Ref: Ceccaldi et al. Nat Rev Genet 2016 17:147 NHEJ HDR; Symington Lenski Annu Rev Genet; Alberts.

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Cell Division

The G2 phase is characterized by:

G2 phase is second gap phase dedicated to growth, quality surveillance, and accumulation of components required for mitosis. After S phase completes DNA synthesis, cells continue protein synthesis, particularly tubulin alpha/beta heterodimers and gamma-tubulin ring complex proteins for spindle assembly, histone variants H2AZ for chromatin stability, and membrane lipid synthesis for organelle expansion. Centrosomes duplicated during S phase mature in G2 by recruitment of pericentriolar material including pericentrin, Cep192, and Cdk5Rap2, acquiring ability to nucleate large astral microtubule a

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 17, G2 as Preparation for M Phase.

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Cell Cycle Regulation

Which DNA repair pathway is activated by ATM after detecting double-strand breaks?

Double-strand breaks present challenging repair choice between rapid but error-prone non-homologous end joining and accurate homologous recombination available only when sister chromatid present. ATM kinase activated by MRN complex phosphorylates H2AX, creating gamma-H2AX domains that recruit mediator 53BP1, which in turn favors end joining by blocking resection. In G1 phase when homologous template absent, ATM-53BP1 axis directs breaks toward classical non-homologous end joining pathway that directly ligates ends after minimal processing by Ku70/Ku80 heterodimer, DNA-PKcs, and XRCC4-DNA ligas

Ref: Marechal & Zou, Genes Dev 2013, DNA Damage Response; Scully et al., Cell 2019, DSB Repair Choice.

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Cell Cycle Regulation

Which component of the DNA damage response (DDR) is associated with single-strand DNA breaks?

Different lesions within DNA damage response activate distinct kinase cascades tailored to repair requirements. Single-strand breaks, gaps, and regions of single-stranded DNA generated when replication forks stall at UV photoproducts or chemical adducts expose stretches of RPA-coated ssDNA that recruit ATR-ATRIP complex and auxiliary proteins TopBP1 and ETAA1. ATR, ataxia telangiectasia and Rad3-related kinase, then phosphorylates CHK1 at serine 317 and 345, leading to degradation of Cdc25A and inhibition of CDK2 to slow S-phase progression and allow repair via homologous recombination or tran

Ref: Cimprich & Cortez, Nature Rev Mol Cell Biol 2008, ATR: Essential Regulator of Genome Integrity; Zou & Elledge, Science 2003, ATR Activation.

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