UKPSC Prelims 2025 General Studies Paper-I · Question 41 of 149

Correct — A, CRISPR.

CRISPR is a gene-editing system. A short guide RNA is written to match a chosen stretch of DNA and steers the Cas9 enzyme to cut precisely there, after which the cell's own repair machinery disables or rewrites that stretch.

Because the guide is designed from a sequence, it can in principle be aimed at the particular mutation an individual carries. Where that is done, the treatment follows from that person's genome readout rather than from the disease label alone.

Personalised medicine, in this sense, means a therapy programmed from the patient's own DNA sequence.

• (b)
  Nanotechnology — Nanotechnology engineers matter at roughly 1–100 nanometres. In medicine it supplies carriers and probes: lipid nanoparticles that ferry mRNA or editing machinery into cells, targeted drug capsules, nanoscale contrast agents.

  It is the right answer to how a genetic payload is delivered into the body's cells. The carrier is the container, not the instruction — the same nanoparticle can carry a different payload for a different patient.

• (c)
  Robotics — Robotics puts machines into the operating theatre and the laboratory: instruments that translate a surgeon's hand movement into scaled, tremor-filtered motion through small incisions, and arms that handle samples in high-throughput testing.

  It is the right answer to which technology gives a surgeon precise, minimally invasive instrument control. Its precision is mechanical and geometric, measured in instrument travel rather than in DNA bases.

• (d)
  Bioprinting — Bioprinting deposits bio-inks loaded with living cells layer by layer, following a digital model, to build tissue-like constructs for grafts, drug testing and research.

  It is the right answer to which technology fabricates tissue by printing living cells. A print can indeed be customised to one person — typically through their own cells and their scan-derived anatomy — but that customisation is structural, while the stem anchors personalisation to genetic make-up.

Personalised medicine treats a patient's own biology — most sharply, their DNA sequence — as the input that decides the therapy, instead of prescribing by disease label alone.

Gene editing acts on that input directly. CRISPR–Cas9 borrows a bacterial defence system: a guide RNA base-pairs with a matching DNA stretch, the Cas9 nuclease cuts there, and the cell's repair machinery then disables or rewrites the sequence.

• CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats, DNA sequences found in bacteria and archaea as part of a defence system against invading viruses.
• In CRISPR–Cas9 editing, a guide RNA base-pairs with the matching DNA sequence and directs the Cas9 enzyme to cut the double strand at that site.
• Emmanuelle Charpentier and Jennifer Doudna received the 2020 Nobel Prize in Chemistry for the development of a method for genome editing.
• The US FDA approved Casgevy (exagamglogene autotemcel), a CRISPR-based therapy, for sickle cell disease in December 2023 and for transfusion-dependent beta-thalassaemia in January 2024.
• Casgevy is made from the patient's own blood-forming stem cells, which are edited outside the body and infused back.
• Somatic gene editing changes cells in the treated person alone; germline editing changes eggs, sperm or embryos and can be inherited.
• Lipid nanoparticles are nanoscale carriers used to move genetic material such as mRNA into cells.
• Bioprinting builds tissue-like structures by depositing bio-inks containing living cells layer by layer from a digital model.

• Reading 'personalised' as merely 'made for one person' and settling on bioprinting because a printed graft can use that patient's own cells — the stem ties personalisation to genetic make-up, which is the sequence itself.
• Picking nanotechnology because lipid nanoparticles carry gene therapies; the carrier is shared across patients, while the genetic instruction inside it is the part that can be written for the individual.
• Treating CRISPR as a purely laboratory technique, and so rejecting it as an answer about medicine, when it already underlies an approved therapy.
• Blurring gene therapy with gene editing: supplying a working copy of a gene through a vector is gene therapy, whereas CRISPR alters the sequence at its own location in the genome.
• Assuming an edit made in a patient's body cells will be inherited — that follows only from germline changes, not somatic ones.

• practice — not a real PYQ

  CRISPR–Cas9, as used in genome editing, is best described as

  • (a)a nanoscale capsule that carries a drug to a target tissue
  • (b)a guide RNA paired with a nuclease that cuts a matching DNA sequence
  • (c)a printer that deposits living cells layer by layer to form tissue
  • (d)a robotic arm that performs incisions under a surgeon's control
  Answerb — the specificity of CRISPR editing comes from base-pairing: the guide RNA finds the matching DNA stretch and the Cas9 nuclease cuts there.

  Option (a) describes a nanoparticle drug carrier, (c) describes bioprinting, and (d) describes a surgical robot; none of the three changes a DNA sequence.

• practice — not a real PYQ

  The 2020 Nobel Prize in Chemistry was awarded for the development of a method for genome editing. It was shared by

  • (a)Emmanuelle Charpentier and Jennifer Doudna
  • (b)Katalin Karikó and Drew Weissman
  • (c)John Gurdon and Shinya Yamanaka
  • (d)Har Gobind Khorana and Marshall Nirenberg
  Answera — Charpentier and Doudna were awarded the 2020 Chemistry prize for the genome-editing method built on CRISPR–Cas9.

  Karikó and Weissman won the 2023 prize in Physiology or Medicine for nucleoside base modifications that made mRNA vaccines possible. Gurdon and Yamanaka won in 2012 for reprogramming mature cells to pluripotency. Khorana and Nirenberg shared the 1968 prize, with Robert Holley, for work on the genetic code.

• practice — not a real PYQ

  With reference to gene editing, consider the following statements: 1. In CRISPR–Cas9, the target site is recognised by base-pairing between a guide RNA and the DNA. 2. Cas9 acts as an enzyme that cuts DNA. 3. An edit made in a patient's somatic cells is passed on to that patient's children. Which of the statements given above is/are correct?

  • (a)1 only
  • (b)1 and 2 only
  • (c)2 and 3 only
  • (d)1, 2 and 3
  Answerb — statements 1 and 2 describe how the system works: the guide RNA supplies the address by base-pairing, and Cas9 supplies the cut.

  Statement 3 is wrong, which rules out (c) and (d). Somatic edits are confined to the treated person's body cells; inheritance would require a change in the germline. Option (a) fails because it drops the true statement 2.

• practice — not a real PYQ

  Bioprinting is distinguished from conventional 3D printing chiefly by the fact that it

  • (a)needs no digital model of the object being made
  • (b)uses bio-inks containing living cells to build tissue-like constructs
  • (c)fuses metal powder using a laser beam
  • (d)works only at the nanometre scale
  Answerb — the defining feature is the material: bio-ink carrying living cells, deposited layer by layer to form tissue-like structures.

  Option (a) is wrong because bioprinting follows a digital model just as other additive manufacturing does. Option (c) describes laser powder-bed fusion of metals. Option (d) misstates the scale, which runs from micrometres to millimetres.