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X-ray diffraction photos of DNA helped to solve the puzzle of
reproduction
1953: Scientists describe 'secret of life'
England have
Two Cambridge University scientists have published their answer to one of
the most fundamental questions of biology - how do living things reproduce
themselves?
In an article published today in Nature magazine, James D Watson and
Francis Crick describe the structure of a chemical called deoxyribonucleic acid,
or DNA.
DNA is the material that makes up genes which passhereditarycharacteristics
from one parent to another.
In short, it consists of a double helix of two strands coiled around each
other. The strands are made up of complementary elements that fit together and
when uncoiled can produce two copies of the original.
Momentous discovery
This special property for accurate self-replication allows DNA to duplicate
the genes of an organism during the nuclear divisions for growth and the
production of germ cells for the next generation.
They began their article with the modest statement: "We wish to suggest a
structure for the salt of deoxyribose nucleic acid (DNA). This structure has
novel features which are of considerable biological interest."
On 28 February, Mr Crick walked into a Cambridge pub with Mr Watson to
celebrate the fact that they had unravelled the structure of DNA, saying: "We
have discovered the secret of life!"
The momentous discovery was the culmination of research by Medical Research
Council scientists Maurice Wilkins and Rosalind Franklin in London, who produced
X-raydiffractionphotographs and other evidence.
The US Embassy in Tehran was seized by Islamic militants on 3 November
1979
1980: Tehran hostage rescue mission fails
Artificially 1969:
The
A top-secret attempt by the United States to free American hostages held in
Iran's capital,Tehran, has collapsed in failure, with the death of eight
soldiers.
President Carter announced the disastrous mission in a broadcast to the
nation earlier today.
"I ordered this rescue mission prepared in order to safeguard American
lives and protect America's national interests, and to reduce the tensions in
the world that have been caused among many nations as this crisis has
continued," he said.
He took full personal responsibility for the operation, and its
cancellation, but did not rule out another attempt.
It was the first the American public, or the wider world, had heard of the
mission, although it had been planned since shortly after the US embassy in Iran
was seized last November by Islamic militants. They have held 53 US citizens
hostage there ever since.
The dramatic attempt to free the hostages began yesterday when six Hercules
C130 transport planes set off torendezvouswith a group of nine helicopters at a
remote desert airstrip, south-east of Tehran.
But the mission ran into trouble almost as soon as it had started.
From farce to tragedy
Two helicopters went down with engine trouble, and a third was diverted to
help.
Then another helicopter was damaged as it landed on the airstrip, leaving
only five workable helicopters. The mission had become impossible.
President Carter ordered the operation to abort. It was then that the farce
became a tragedy.
As the aircraft took off again, another helicopter crashed into one of the
C130 aircraft and burst into flames. Eight soldiers died, and another four men
suffered burns.
"An act of war"
In Tehran there were jubilant scenes as thousands of people celebrated the
failure of the mission.
The Foreign Minister, Sadeq Qotbzadeh, condemned the rescue effort as "an
act of war".
In Europe, there was shock and surprise that the mission had taken place
without advance consultation of America's allies.
EEC governments have recently agreed to threaten sanctions against Iran in
the hope of preventing the use of force.
Vocabulary:
hereditary:passing down from inheritance(世袭的，遗传的)
diffraction:change in the directions and intensities of a group of waves
after passing by an obstacle or through an aperture(衍射)
rendezvous:a prearranged meeting place, especially an assembly point for
troops or ships (指定集合地点) |
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发表于 2016-7-9 23:48:09