Deoxyribonucleic acid (DNA) is a vital component of both eukaryotic and prokaryotic cells. A blueprint is a detailed drawing or map which identifies and directs the construction and development of a building or an object. DNA is the hereditary material in almost all organisms.
Nearly every cell in an organism’s body has the same DNA. DNA is the blueprint that guides the construction and development of living organisms. Some viruses have RNA as their genetic code. DNA structure DNA is a polymer, made up of many monomers called nucleotides which link together by condensation reactions. A nucleotide is composed of a pentose sugar called deoxyribose, a phosphate group and a nitrogenous base. Nucleotides link together by a phosphodiester bond. Four types of bases occur in DNA. Two of the bases are purines – adenine and guanine.
The pyrimidines are thymine and cytosine. The pyrimidines are single ringed and the purines are double ringed. DNA is composed of two antiparallel strands which are wound round each other in a right handed manner to form a double helix. In each strand the sugar and phosphate alternate to form a backbone and the bases are linked to the sugar. The two strands are held together by hydrogen bonds that occur between the bases. The way that bases link together is called complementary base pairing, where adenine always pairs up with thymine and guanine with cytosine.
The base pairing is called complementary because there are specific geometry requirements in the formation of hydrogen bonds between the bases. This way of pairing, ensures that the bases fit in the space between the two strands. Two hydrogen bonds form between adenine and thymine and three between cytosine and guanine. DNA as the “Blueprint” The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of blueprints or a recipe, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules.
The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information. It is the sequence of the four bases along the backbone that encodes information. This information is read using the genetic code, which specifies the sequence of the amino acids within proteins. The four chemical bases of DNA have been arranged and rearranged in numerous combinations to create the genomes, of almost every creature that has ever lived.
The human genome is a complete copy of the entire set of human gene instructions. The Human Genome Project, completed in 2003, identified all the human genes in DNA and stored the information in databases so all researchers everywhere could use it. Genes comprise only about 2% of the human genome; the remainder consists of noncoding regions, whose functions may include providing chromosomal structural integrity and regulating where, when, and in what quantity proteins are made. The human genome is estimated to contain 30,000 – 40,000 protein coding genes.
The average gene consists of 3000 bases, but sizes vary greatly, with the largest known human gene being 2. 4 million bases. The code is read by copying stretches of DNA into the mRNA, in a process called transcription. A protein is then formed on a ribosome in a process known as translation. Proteins are the working molecules inside cells. They play many roles within a cell by forming structures and regulating metabolism.
Cells in different parts of the body produce different types of proteins even though they have the same DNA. This is because only those enes that are switched on lead to the formation of the protein they code for. Certain genes in eukaryotic cells, called split genes, are composed of introns and exons. mRNA formed from such genes also contain these regions. However, the introns must be removed before the mRNA moves out of the nucleus. The way in which exons are joined determines the type of polypeptide formed. Thus the presence of introns and exons lead to the ability of DNA to store a lot of information. Features of the genetic code A sequence of three bases on the DNA molecule codes for one amino acid.
For this reason the term triplet code is used. The code is almost universal, that is the sequence of bases codes for the same amino acid in all organisms. Most amino acids are specified by more than one codon, i. e. the code is degenerate. In fact, only methionine and trptophan are specified by a single codon. There are no gaps between codons and they do not overlap. In general, no codon specifies more than one amino acid. Start and stop codon specify the initiation and end of formation of a polypeptide. DNA is referred to as “blueprint” as it codes for proteins which are the molecules that do work within the cell.