Genetic Engineering :What Is DNA?
Every living thing is made up of cells and the products of cells. If you take a magnifying glass, you can see the cells in a plant leaf. An organism may have many different kinds of cells, making up different kinds of tissues, but nearly all cells contain a nucleus at the center. Within the nucleus we find the x-shaped structures called chromosomes, made of DNA strands all coiled up and surrounded by protein. Hum ans have forty-six chromosomes, and a human strand of DNA is a little over two yards long if it is pulled out and completely uncoiled. linseed plant cells have thirty chromosomes. Bacteria are simpler, without the nucleus or the protein wrapping around the DNA, but the concept is roughly the same.
CLEARLY DEMON STARING ITS DOUBLE-HELIX STRUCTURE.
When people describe DNA’s job, they commonly say DNA supplies the “blueprint” for building living things. However, that expression may be misleading. DNA is not a sketch or diagram like a blueprint. It is actually a physical object—a very small object, but still an object that can be broken or snapped off, just as one might break a piece of thread. Nearly every cell in every organism contains DNA. Every cell of a mountain lion crouching in a tree, every cell of the tree, every bacterium, and every mouthful you eat of a tomato contains DNA. it does not matter whether the lion was born in a zoo or in a mountainside cave, it does not matter whether the tomato came from an organic farmer at a produce market or from a large corporation’s warehouse. it still has DNA in its cells
physically, a gene is a section ot DNA. A gene is a unit of biological information. You might say that DNA is the recipe book and a gene represents one recipe in the book. Each gene builds a particular protein. The ingredients for the gene’s recipe are floating around in the cell—they arc called amino acids. (Amino acids make up two groups of about twenty different molecules that arc commonly found in every living cell.) The gene carries the instructions for putting them together in a structured pattern to form a chain of amino acids that make up a particular protein, such as an enzyme that starts chemical processes going. All the traits of any organism—your brother, a bacterium, that mountain lion—are created by the presence or absence of a particular protein. The full set of a living thing’s genetic information is called the genome,
and every cell of an organism contains the same genome..
This becomes obvious if you snip off a few leaves from a Swedish ivy plant, stick each leaf stalk in a small pot of damp soil, and then cover the whole thing with a plastic cap. In a few days, new Swedish ivy plants spring up from the detached leaves—showing that the instructions for growing the whole plant were present in the cells of the planted leaves. As many as 20,000 different proteins may be present in a single cell. Each one has a different job and is the creation of a different gene recipe. The human gcnome
consists of some 60,000 to 90,000 genes. These differ ntrecipes give humans the ability to build all those proteins. However, each individual organism is different, with subtle differences in its DNA. All DNA is made up of four bases arranged in different sequences. These sequences arc identical in identical twins (twins that come from the same egg). Otherwise, differences exist in every individual hum an’s DNA. Yet the language of DNA is understood by all living things. A mouse cell can read the instructions from a gene inserted from a human. A human cell understands recipes recorded in a gene from a mouse. The following four points provide some keys to understanding how genetic engineering works. Molecular geneticist Alan McHughcn calls these points “the four fundamental pillars of genetics.
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