DNA The Making Essay Research Paper DNA

DNA: The Making Essay, Research Paper

DNA: The Making

Lyle Sykes

For more than 50 years after the science of genetics was established and the

patterns of inheritance through genes were clarified, the largest questions

remained unanswered: How are the chromosomes and their genes copied so exactly

from cell to cell, and how do they direct the structure and behavior of living

things. This paper will discuss those questions and the people that answered

them. Two American geneticists, George Wells Beadle and Edward Lawrie Tatum,

provided one of the first important clues in the early 1940s. Working with the

fungi Neurospora and Penicillium, they found that .genes direct the formation of

enzymes through the units of which they are composed.. (Annas 1996) Each unit (a

polypeptide) is produced by a specific gene. This work launched studies into the

chemical nature of the gene and helped to establish the field of molecular

genetics. “The fact that chromosomes were almost entirely composed of two kinds

of chemical substances, protein and nucleic acids, had long been known. Partly

because of the close relationship established between genes and enzymes, which

are proteins, protein at first seemed the fundamental substance that determined

heredity.. (Goetinck 1995) .In 1944, however, the Canadian bacteriologist Oswald

Theodore Avery proved that deoxyribonucleic acid (DNA) performed this role. He

extracted DNA from one strain of bacteria and introduced it into another strain.

The second strain not only acquired characteristics of the first but passed them

on to subsequent generations. By this time DNA was known to be made up of

substances called nucleotides. Each nucleotide consists of a phosphate, a sugar

known as deoxyribose, and any one of four nitrogen-containing bases. The four

nitrogen bases are adenine (A), thymine (T), guanine (G), and cytosine

(C).”(Caldwell 1996) “In 1953, putting together the accumulated chemical

knowledge, geneticists James Dewey Watson of the U.S. and Francis Harry Compton

Crick of Great Britain worked out the structure of DNA. This knowledge

immediately provided the means of understanding how hereditary information is

copied. Watson and Crick found that the DNA molecule is composed of two long

strands in the form of a double helix, somewhat resembling a long, spiral ladder.

The strands, or sides of the ladder, are made up of alternating phosphate and

sugar molecules. The nitrogen bases, joining in pairs, act as the rungs. Each

base is attached to a sugar molecule and is linked by a hydrogen bond to a

complementary base on the opposite strand.. (Caldwell 1996) .Adenine always

binds to thymine, and guanine always binds to cytosine.. (Annas 1996) .To make a

new, identical copy of the DNA molecule, the two strands need only unwind and

separate at the bases (which are weakly bound); with more nucleotides available

in the cell, new complementary bases can link with each separated strand, and

two double helixes result. Since the .backbone. of every chromosome is a single

long, double-stranded molecule of DNA, the production of two identical double

helixes will result in the production of two identical chromosomes.” (Caldwell

1996) “The DNA backbone is actually a great deal longer than the chromosome but

is tightly coiled up within it. This packing is now known to be based on minute

particles of protein known as nucleosomes, just visible under the most powerful

electron microscope. The DNA is wound around each nucleosome in succession to

form a beaded structure. The structure is then further folded so that the beads

associate in regular coils. Thus, the DNA has a .coiled-coil. configuration,

like the filament of an electric light bulb.” (Popper 1996) “After the

discoveries of Watson and Crick, the question that remained was how the DNA

directs the formation of proteins, compounds central to all the processes of

life. Proteins are not only the major components of most cell structures, they

also control virtually all the chemical reactions that occur in living matter.

The ability of a protein to act as part of a structure, or as an enzyme

affecting the rate of a particular chemical reaction, depends on its molecular

shape. This shape, in turn, depends on its composition. Every protein is made up

of one or more components called polypeptides, and each polypeptide is a chain

of subunits called amino acids. Twenty different amino acids are commonly found

in polypeptides.. (Caldwell 1996) .The number, type, and order of amino acids in

a chain ultimately determine the structure and function of the protein of which

the chain is a part.” (Marx 1996) “Since proteins were shown to be products of

genes, and each gene was shown to be composed of sections of DNA strands,

scientists reasoned that a genetic code must exist by which the order of the

four nucleotide bases in t

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