Why does cdna not have introns

Since each deoxyribose in a DNA chain is coupled to one of the four nitrogenous bases G, A, T, or C , these long chains can carry information. Codons are used to call for specific amino acids to be bonded together to form proteins. For instance the codon adenosine-adenosine-guanosine AAG calls for the amino acid lysine lys to be incorporated into a protein molecule.

The codon AGG calls for the amino acid arginine arg. There are also codons that, under the right circumstances, call for a protein to begin to be formed start codons , or for a protein chain to be finished stop codons. As you can see from this simple example, DNA can carry a massive amount of information. Figure 1: Adenine binds to thymine; guanine binds to cytosine. A gene is a set of codons that specify a specific protein chain, along with the associated start and stop codons.

In nature, the process for information to be passed on from DNA can occur through either replication or gene expression. There are some important factors to note:. Initially, it was observed that gDNA was always read and transcribed into mRNA, which guided protein formation and then was disposed.

Calling it that challenged scientists to find exceptions to this rule. What is mRNA made of? The mRNA is an RNA version of the gene that leaves the cell nucleus and moves to the cytoplasm where proteins are made.

DNA is a generic term for deoxyribonucleic acid, which makes up genetic material. These reaction products can be used for direct cloning without amplification. Why are introns called introns? The parts of the gene sequence that are expressed in the protein are called exons, because they are expressed, while the parts of the gene sequence that are not expressed in the protein are called introns, because they come in between the exons.

Does mRNA have introns? The pre-mRNA molecule thus goes through a modification process in the nucleus called splicing during which the noncoding introns are cut out and only the coding exons remain. Is reverse transcriptase a DNA polymerase? Reverse Transcriptase. The mRNA can be extracted from cells of specific tissues from the organism of interest.

Because of the different starting material, cDNA libraries will have some key distinctions from a genomic library. The reasons for the differences above are because of the nature of gene expression. Furthermore, if the mRNA is isolated from the cytoplasm of eukaryotes, intron sequences will have been removed and will not be copied into a cDNA clone.

Thus the cDNA clone will be missing parts of the gene sequence.