Complimentary Dna (Cdna) and Rna (Crna)
Deoxyribonucleic acid (DNA) is composed of four types of nucleotide bases: adenine (A), cytosine (C), guanine (G) and thymine (T). The adenine (A) on one strand always pairs with the thymine (T) on the other strand, whereas cytosine (C) always pairs with guanine (G). The two strands are said to be complementary to one another. Accordingly, complimentary DNA (cDNA) is a copy of a strand of DNA containing a sequence of bases that bind to the original molecule. For example, if the original DNA stand had a base sequence of ATT, the complimentary DNA strand would carry a base sequence of TAA.
The production of complementary DNA is central to the replication of DNA, the making of two copies of the double stranded entity. In the process of DNA replication, the two strands are unzipped or unwound and molecules called DNA polymerases run along each strand, making a copy of each. Accordingly, each strand itself acts as a template to produce a complimentary strand. Because the two new strands will be complimentary to one another, they can associate with each other. This process is termed annealing. The old strands can also anneal. Thus, two complete copies of DNA are produced from one copy in a process referred to as semiconservative replication.
Ribonucleic acid (RNA) is composed of four types of nucleotide bases: adenine (A), cytosine (C), guanine (G) and uracil (U) instead of the thymine (T) found in DNA. The adenine (A) on one strand always pairs with the uracil (U) on the other strand, whereas cytosine (C) always pairs with guanine (G). The two strands are said to be complementary to one another. Accordingly, complimentary RNA (cRNA) is a copy of a strand of RNA containing a sequence of bases that bind to the original molecule. For example, if the original RNA stand had a base sequence of AUU, the complimentary RNA strand would carry a base sequence of UAA.
Complimentary RNA (cRNA) is also a term used to designate RNA which is complimentary to one of the DNA strands of the double helix. Used in this manner the molecule is more often termed messenger RNA (mRNA).The formation of mRNA is vital for the manufacture of proteins coded for by regions within the DNA. The mRNA is the template for the production of protein in the process of translation.
The annealing of a DNA or RNA strand to its complement is one of the most specific molecular recognition events known in biology. The phenomenon has been exploited in many approaches to conduct basic research. Nucleic acid blotting techniques have greatly facilitated the understanding of gene organization and development. In blotting, DNA fragments are immobilized on a solid support and a probe termed a radioactive oligonucleotide probe that contains the sequence of interest is exposed to the support. The binding (annealing) of the probe sequence to the complementary immobilized sequence detects the counterpart.
Recently, the use of fluorescently labeled, single strand probes, termed molecular beacons successfully allowed the detection of target DNA sequences as they were synthesized and could detect the synthesized species within living cells. Binding of the probe to the target activates the fluorescence reaction; unbound probe remains "dark". Such detection without separation permits real-time monitoring of DNA synthesis. Other potential applications for anneal-based molecular beacons are the identification of genetic alleles and specific strains of infectious agents.
A now classic use (exploitation) of complementary DNA and the annealing process is the technique of polymerase chain reaction (PCR). PCR mimics the cellular process in a test tube. The entire process is quite rapid, taking less than five minutes. With the reagents available in the test tube, 30 or so reactions can take place. And, each new DNA copy generated can itself act as a template to produce a complimentary copy. After thirty cycles, a single piece of DNA can produce a billion copies. Another use the phenomenon of annealing has been put to is by lab enforcement laboratories, which specialize in DNA analysis. The process whereby a piece of DNA recognizes its complimentary sequence and anneals with it can be used to isolate DNA from a mixture of DNA species. A final example is the design and manufacture of a tomato in which ripening can be delayed. To accomplish this, the mRNA of the compound which ripens tomatoes was determined and its corresponding DNA sequence determined. A complimentary or antisense version was produced. The antisense DNA is inserted into the genome; both the normal RNA and complimentary RNA are produced. They stick together, negating the production of the ripening compound.
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