Genetic Engineering - Cloning, DNA, Stem Cells Pros and Cons
Molecular genetics


The future technology

DNA and Genes

A gene is a discrete sequence of DNA nucleotides.

Gene regulatory segment, promoter, introns, exons

Mendel described a gene as a discrete unit of heredity that influences a visible trait. Beadle and Tatum defined a gene as the directions fro making a single protein, which influences a metabolic trait.

Early sequencing efforts showed that proteins are, in turn, long chains of amino acids arranged in a specified order. The triplet genetic code future refined the definition of a gene as a discrete sequence of DNA encoding a protein beginning with a "seat" codon and ending with a "stop" codon.

Gene analysis took a giant step forward with the discovery of methods to determine the exact sequence of nucleotides that compose a specific gene. DNA sequencing was built upon earlier knowledge of DNA polymerizes and cell-free systems for replicating DNA.

The chain-termination method, which makes clever use of a "defective" DNA nucleotide, now dominates DNA sequencing technology.

Without a sophisticated technique for determines base sequence, one can't distinguish bacterial DNA from human DNA. This is because all DNA molecules have the same general chemical properties and physical structure.

Proteins, by comparisons, are a much more diverse group of molecules with a much greater complexity of structure and function.

In his account of the discovery of the double helix, crick referred to this difference when he said that "DNA is, at bottom, a much less sophisticated molecule than a highly evolved protein and for this reason reveals its secrets easily."

There are four basic DNA "secrets", embodied in four questions:

  1. How does the molecule carry information?
  2. How is that information copied for transmission to future generations?
  3. What mechanisms allow the information to change?
  4. How does the information govern the expression of phenotype?

The double helical structure of DNA provides a potential solution to each of these questions, endowing the molecules with the capacity to carry out all the critical functions required of the genetic material.

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