Photo 51 refers to an image of
- (a)a crater on the Moon
- (b)DNA molecules
- (c)the virus responsible for COVID-19
- (d)the virus responsible for common cold
Correct — B, DNA molecules. 'Photo 51' is the name given to a single X-ray diffraction photograph of the B-form of DNA, recorded at King's College London in 1952 by the research student Raymond Gosling working in Rosalind Franklin's group. It is not a picture of a molecule in the ordinary sense — X-rays scattered by the fibre of DNA fall on the film as a pattern of spots, and the blurred X of spots across the middle is the diffraction signature of a helix. That pattern, together with the spacing of the horizontal layer lines, gave the repeat distance along the helix and the stacking distance between the bases, and it was the decisive piece of evidence behind the double-helix model of DNA that Watson and Crick published in Nature in April 1953 — in the same issue as Franklin and Gosling's own paper reporting the photograph.
- (a)a crater on the Moon — Photo 51 is a laboratory X-ray diffraction plate exposed inside a King's College London basement, not an astronomical photograph; lunar craters are imaged by telescope and by spacecraft cameras.
- (c)the virus responsible for COVID-19 — SARS-CoV-2 was identified only in 2020, some sixty-eight years after Photo 51 was taken, and the familiar images of it are electron micrographs rather than X-ray diffraction patterns.
- (d)the virus responsible for common cold — The rhinoviruses behind the common cold were isolated and imaged well after 1952 and by other techniques; no photograph of them carries the name Photo 51.
X-ray crystallography works by firing X-rays at an ordered sample and recording how they scatter. The scattering pattern is not a picture of the molecule, but the geometry of the molecule can be reconstructed from it. When the sample is a fibre of DNA held at high humidity — the so-called B-form — the pattern that comes out is a cross of smeared spots, which is what a helical structure produces, with the vertical spacing of the layer lines fixed by the pitch of the helix. Photo 51 showed that cross with unusual clarity.
The four options separate cleanly by date and by technique. Photo 51 belongs to 1952, so anything involving COVID-19 is ruled out at once, and X-ray diffraction is a laboratory technique applied to matter in the hand, which rules out the Moon. That leaves a molecule, and DNA is the molecule the phrase has always referred to. The history behind the item is worth knowing on its own: Franklin and Gosling's photograph was shown to James Watson without her knowledge, and the 1962 Nobel Prize in Physiology or Medicine went to Watson, Crick and Maurice Wilkins. Franklin had died in 1958, and the Nobel Prize is not awarded posthumously, so she could not be named.
- Photo 51 is an X-ray diffraction photograph of the B-form of DNA taken at King's College London in 1952 by Raymond Gosling in Rosalind Franklin's group.
- The X-shaped array of spots in the photograph is the diffraction pattern characteristic of a helix.
- Watson and Crick's double-helix model appeared in Nature on 25 April 1953, in the same issue as Franklin and Gosling's paper on the diffraction data.
- The 1962 Nobel Prize in Physiology or Medicine for the structure of nucleic acids was shared by Watson, Crick and Maurice Wilkins; Franklin had died in 1958 and the prize is not given posthumously.
- Assuming Photo 51 is a microscope image of DNA; it is a diffraction pattern, and the molecule is inferred from it rather than seen.
- Attributing the photograph to Watson and Crick, who interpreted it but did not take it.
- Being pulled towards the COVID-19 option because the phrase sounds recent — the photograph is from 1952.
Asked as a one-line recall item on a famous named image; the same history is more often tested through the scientists and the 1962 Nobel Prize.
Which of the following features of DNA makes it uniquely suited to store and transmit genetic information from generation to generation?
- (a) Complementarity of the two strands
- (b) Double helix
- (c) Number of base pairs per turn
- (d) Sugar phosphate backbone
Answer(a) Complementarity of the two strands — complementary base pairing lets each strand act as a template, so the information copies faithfully.
Goes to the structure that Photo 51 revealed, and asks which feature of it actually does the work of heredity.
Who among the following shared the Nobel Prize in 1962 along with Francis Crick and James Watson for their discoveries concerning the molecular structure of nucleic acids ?
- (a) Erwin Chargaff
- (b) Maurice Hugh Frederick Wilkins
- (c) Rosalind Franklin
- (d) Phoebus Levene
Answer(b) Maurice Hugh Frederick Wilkins
The same King's College London X-ray work seen from the other end — who was recognised for it in 1962, and why Franklin was not.
- practice — not a real PYQ
The X-shaped pattern of spots seen in an X-ray diffraction photograph of B-form DNA indicates which structural feature?
- (a)A helix
- (b)A flat sheet
- (c)A closed ring
- (d)A branched chain
Answer(a) A helix — a helical molecule scatters X-rays into a characteristic cross of spots, which is what Photo 51 shows.
- practice — not a real PYQ
In which year did Watson and Crick publish their model of the double-helical structure of DNA in Nature?
- (a)1944
- (b)1953
- (c)1962
- (d)1972
Answer(b) 1953 — the paper appeared in Nature in April 1953; the Nobel Prize for the work followed in 1962.