Archive for the ‘Cancer Biology’ Category
Thursday, July 3rd, 2008
DNA is mixed with short (10–20 base) single-stranded oligonucleotide primers that are complementary
to the 5′ and 3′ ends of the sequence to be amplified. The mixture is heated to dissociate or “melt” all double-stranded DNA, and then cooled to permit the primers to anneal to their complementary sequences on the ...
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Thursday, July 3rd, 2008
The nucleotide sequence of a gene’s coding region encodes the amino acid sequence of its protein. This means that even in the absence of any knowledge about a gene’s protein, we can predict the structure of that protein given the nucleotide sequence of the gene. How can the nucleotide sequence ...
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Thursday, July 3rd, 2008
One application for Southern blotting is the direct demonstration of physical linkage between two genes. If two different gene probes were to hybridize to the same restriction fragment in a Southern blot, this would prove that the loci of the two genes were closely linked. Unfortunately, eukaryotic genetic linkages ordinarily ...
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Sunday, June 1st, 2008
SOUTHERN BLOTTING
One of the most useful techniques for analyzing a gene at the level of genomic DNA is Southern blotting, named for its originator, E.M. Southern.18 In general, it allows one to determine whether specific nucleotide sequences in a cloned probe are present in a sample of genomic DNA. The ...
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Sunday, June 1st, 2008
We shall see in the following sections that what lies at the heart of gene analysis is the ability to identify a specific gene (or mRNA) in a complex mixture of all the DNA (or RNA) in a cell or tissue. This can only be done when one already has ...
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Sunday, June 1st, 2008
One exceptional application of these techniques has been the construction of gene libraries. A gene library contains the entire complement of DNA (and therefore genes) from an organism in the form of DNA fragments inserted into recombinant plasmids or phages. DNA containing an organism’s genes (i.e., genomic DNA) can be ...
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Sunday, June 1st, 2008
In eukaryotic chromosomes, individual molecules of DNA are several million base pairs long. Because these molecules are far too large to analyze directly, scientists are usually interested in cutting DNA into fragments of manageable size. Fortunately, for molecular biologists, bacteria have evolved a highly diverse set of enzymes, the “restriction ...
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Sunday, June 1st, 2008
In eukaryotes, the coding regions of most genes are not continuous. Rather, they consist of areas that are transcribed into mRNA, the “exons,” which are interrupted by stretches of DNA that do not appear in mature mRNA, the “introns”. The functions of introns are not known with certainty. A purpose ...
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Sunday, June 1st, 2008
The basic repeating units of the DNA polymer are nucleotides (Figure ). Nucleotides consist of an invariant portion, a five-carbon deoxyribose sugar with a phosphate group, and a variable portion, the “base.” Of
the four bases that appear in the nucleotides of DNA, two are purines, adenine (A) and guanine (G), ...
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Sunday, June 1st, 2008
Every gene consists of several functional components, each involved in a different facet of the process of gene expression (Figure) Broadly speaking, however, there are two main functional units: the “promoter” region and the “coding” region.
The promoter region controls when and in what tissue a gene is expressed. For example, ...
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