Datasets:
vnpthack
/
vnpt_data

Dataset card Data Studio Files
xet
 Community
1
text
stringlengths
0
6.73k
of chaïns, twisted upon each other. 'Phe backbone of each of these chains, which
are analogous to the chains of proteins but chemically quite different, is a series
of sugar and phosphate groups, as shown in FEig. 3-2. NÑow we see how the chain
can contain instructions, for if we could split this chain down the middle, we
would have a series ĐAADŒ... and every living thing could have a different
--- Trang 77 ---
SỐ | )—BIA— } SUên
Ho ° Q on
tot [ABC] H89
Ho ° ào
3895E [ ap—C |] S85
AC › z2
Ho ° con
s2E [pc CC] N8
2 0 S z9
Ho ọ IG
SIỐN | }—CD—C }] SUêA
Fig. 3-2. Schematic diagram of DNA.
series. Thus perhaps, in some way, the specIfc ?nstrucfions for the manufacture
Of proteins are contained in the specifc ser2es of the DNA.
Attached to each sugar along the line, and linking the two chains together,
are certain pairs of cross-links. However, they are not all of the same kind; there
are four kinds, called adenine, thymine, cytosine, and guanine, but let us call
them 4, Ø, C, and D. 'The interesting thing is that only certain pairs can sit
opposite each other, for example A with and Πwith 2. These pairs are put on
the two chains in such a way that they “ñt together,” and have a sirong energy
Of interaction. However, will not ft with A, and will not ñt with Œ; they
will only fit in pairs, A against and Œ against J. 'Therefore if one is Œ, the
--- Trang 78 ---
other must be D, etc. Whatever the letters may be in one chaïn, each one must
have its specifc complementary letter on the other chain.
'What then about reproduction? Suppose we split this chain in two. How can
we make another one just like it? lf, in the substances of the cells, there is a
manufacturing department which brings up phosphate, sugar, and A, 8, Œ, D
units not connected in a chain, the only ones which will attach to our split chain
will be the correct ones, the complements of ĐAADŒ..., namely, ABC...
'Thus what happens is that the chain splits down the middle during cell division,
one half ultimately to go with one cell, the other half to end up in the other cell;
when separated, a new complementary chain is made by each hal£chain.
NÑext comes the question, precisely how does the order of the A, , Œ, D units
determine the arrangement of the amino acids in the protein? 'This is the central
unsolved problem in biology today. "The first clues, or pieces of information,
however, are these: There are in the cell tiny particles called ribosomes, and it is
now known that that ¡is the place where proteins are made. But the ribosomes
are not in the nucleus, where the DNA and its instructions are. Something seerms
to be the matter. However, it is also known that little molecule pieces come of
the DNA——not as long as the big DNA molecule that carries all the information
itself, but like a small section of it. This is called RNA, but that is not essential.
lt is a kind of copy of the DNA, a short copy. The RNA, which somehow carries
a message as to what kind of protein to make goes over to the ribosome; that is
known. When it gets there, protein is synthesized at the ribosome. 'Phat is also
known. However, the details of how the amino acids come in and are arranged in
accordance with a code that is on the RNA are, as yet, still unknown. We do
not know how to read it. IÝ we knew, for example, the “lineup” A, Ö,CŒ,CŒ, A,
we could not tell you what protein is to be made.
Certainly no subject or fñeld is making more progress on so many fronts at
the present moment, than biology, and iŸ we were to name the most powerful
assumption of all, which leads one on and on in an attempt to understand life, it
1s that all things are mmade oƒ atorms, and that everything that living things do
can be understood in terms of the jigglings and wigglings oŸ atoms.
3-4 Astronomy
In this rapid-fire explanation of the whole world, we must now turn to astron-
omy. Astronomy is older than physics. In fact, it got physics started by showing
the beautiful simplicity of the motion of the stars and planets, the understanding
--- Trang 79 ---
of which was the beginnzng of physics. But the most remarkable discovery in all
OŸ astronomy is that the sfars are made oƒ atoms oƒ the same kind as those on the
carth.* How was this done? Atoms liberate light which has defnite frequencies,
something like the timbre of a musical instrument, which has defnite pitches or
Írequencies of sound. When we are listening to several different tones we can tell
them apart, but when we look with our eyes at a mixture of colors we cannot tell
the parts from which iÿ was made, because the eye is nowhere near as discerning
as the ear in this connection. However, with a spectroscope we cøn analyze the Íre-
quencies of the light waves and in this way we can see the very tunes oŸ the atoms
that are in the diferent stars. As a matter of fact, 6wo of the chemical elements
were discovered on a star before they were discovered on the earth. Helium was
discovered on the sun, whence its name, and technetium was discovered in certain
cool stars. This, of course, permits us to make headway in understanding the
stars, because they are made of the same kinds of atoms which are on the earth.
Now we know a great deal about the atoms, especially concerning their behavior
under conditions of high temperature but not very great density, so that we
can analyze by statistical mechanics the behavior of the stellar substance. Even
though we cannot reproduce the conditions on the earth, using the basic physical
laws we often can tell precisely, or very closely, what will happen. So it is that
physics aids astronomy. 5trange as iÿ may seem, we understand the distribution of
matter in the interior of the sun far better than we understand the interior of the
carth. What goes on ns2đde a star is better understood than one might guess from
the dificulty of having to look at a little dot of light through a telescope, because
we can cdlculate what the atoms in the stars should do in most circumstances.
One of the most impressive discoveries was the origin of the energy of the
stars, that makes them continue to burn. Ône of the men who discovered this
* How Im rushing through this! How much each sentence in this brief story contains. “The
stars are made of the same atoms as the earth.” I usually pick one small topic like this to give a
lecture on. Poets say science takes away from the beauty of the stars—mere globs of gas atoms.
Nothing is “mere.” I too can see the stars on a desert night, and feel them. But do ÏI see less
or more? “The vastness of the heavens stretches my imagination—stuck on this carousel my
little eye can catch one-million-year-old light. A vast pattern—of which I am a part —perhaps
my stuff was belched from some forgotten star, as one is belching there. Or see them with the
greater eye of Palomar, rushing all apart from some common starting point when they were
perhaps all together. What is the pattern, or the meaning, or the œh¿/? It does not do harm to