UPSC Prelims 2021 Q73: What Is ACE2? — Explained
The term 'ACE2' is talked about in the context of
- genes introduced in the genetically modified plants
- development of India's own satellite navigation system
- radio collars for wildlife tracking
- spread of viral diseases
Answer: (d) spread of viral diseases
Statement-wise explanation
- a: incorrect — ACE2 is a protein made by human and animal cells. It is not a transgene used in crop biotechnology. The genes discussed for GM plants are trait genes such as the cry genes from the soil bacterium Bacillus thuringiensis in Bt cotton, which make the plant toxic to bollworms.
- b: incorrect — India's own satellite navigation system is IRNSS, whose operational name is NavIC. It is run by ISRO. Its technical terms are things like IRNSS-1 and NVS satellites, atomic clocks and the L5 and S bands. ACE2 has no role in that programme.
- c: incorrect — Radio collars are GPS, VHF or satellite transmitter collars that track animals such as tigers, elephants and cheetahs. ACE2 is not a tracking device or a collar standard.
- d: correct — ACE2 stands for Angiotensin-Converting Enzyme 2. It is a protein on the surface of cells in the lungs, heart, kidneys and gut. The spike protein of SARS-CoV-2, the virus that causes COVID-19, uses its receptor-binding domain to attach to ACE2 and enter the cell. SARS-CoV, the virus behind the 2003 SARS outbreak, uses the same receptor, so ACE2 comes up whenever scientists discuss how these viruses infect people and spread.
How to eliminate
You cannot reason your way to this answer. It is a pure recall question, so remember one fact: ACE2 (Angiotensin-Converting Enzyme 2) is the cell-surface receptor that SARS-CoV-2 uses to enter human cells. Two clues still help. First, 'enzyme' and 'receptor' are words from biology and medicine, so the satellite and radio-collar options are unlikely. Second, the term was in the news all through 2020–21 because of COVID-19, and a 'Current' tag in a 2021 paper points towards the pandemic. If you only half-remember the term, the GM-plants option is the one that could trap you, because it is also biology. But GM crops are discussed in terms of trait genes such as cry1Ac, not human enzymes.
Know more
ACE2 and how a virus gets into a cell
A virus cannot multiply on its own. It must enter a host cell, and to do that it attaches to a specific molecule on the cell surface, called a receptor. The match between a viral protein and a host receptor decides which species, and which tissues, a virus can infect.
- ACE2 (Angiotensin-Converting Enzyme 2) normally works in the renin–angiotensin system, which controls blood pressure. It converts angiotensin II, which narrows blood vessels, into angiotensin 1-7, which widens them. It is found on cells of the lungs (type II alveolar cells), heart, kidneys, intestine and blood vessels.
- Spike (S) protein: The receptor-binding domain of the SARS-CoV-2 spike binds ACE2. A host enzyme, TMPRSS2, then cuts the spike so the virus can fuse with the cell.
- Why it matters: Spike variants that bind ACE2 more tightly can spread faster. Vaccines and neutralising antibodies work largely by blocking the spike from binding ACE2.
| Virus | Disease | Host receptor |
|---|---|---|
| SARS-CoV-2 | COVID-19 (2019– ) | ACE2 |
| SARS-CoV | SARS (2002–03) | ACE2 |
| HCoV-NL63 | Common cold | ACE2 |
| MERS-CoV | MERS (2012– ) | DPP4 (CD26) |
| HIV | AIDS | CD4 (with CCR5/CXCR4) |
Related terms UPSC can test: spike protein, mRNA vaccine (the vaccine carries the code for the spike), viral vector vaccine (Covishield), inactivated vaccine (Covaxin), zoonosis (spillover from animals; bat coronaviruses use ACE2-like receptors), and variants of concern (Delta, Omicron), which carry spike mutations.
In the news
COVID-19 dominated 2020–21. WHO declared it a pandemic on 11 March 2020, and India's second wave hit in April–May 2021. Research and news reports kept explaining that SARS-CoV-2 enters cells through the ACE2 receptor, which made it a natural current-affairs term for the 2021 paper.
NCERT Concepts to Revise
- Gene Revolution: One option refers to genes put into GM plants. Knowing what Gene Revolution traits look like helps you judge whether ACE2 fits there.
- NavIC: One option refers to India's own satellite navigation system, NavIC/IRNSS. Knowing its terms helps you test that option.