Physico-Chemical Properties of Dna

DNA, as we all know, is esteemed with the title of ‘Master Molecule ’. The three letters of DNA denotes of deoxyribonucleic acid . Now the thing that we ponder on is why DNA is so important to us. Why are the researchers & scientist persistently working on DNA? Why it is so important to know the tiniest details of DNA structure and function.? The simplest answer for â€Å"Why Is DNA Important? † is that DNA is the prerequisite for life’s inception. Firstly, it transfers hereditary information from generation to generation. Secondly, it controls the production of proteins. DNA even determines the structure of the cell, meaning whether it would be a nerve cell or eye cell etc. Our DNA seems to be ultimately responsible for the size, shape and function of every protein that our bodies make. Similarly, the DNA of each plant and animal seems to be ultimately responsible for the size, shape and function of every protein that each of them makes. We will now take a small overview on history, physical properties , chemical properties of DNA. Overview on History : DNA was first isolated by Friedrich Miescher , who in 1869 discovered a microscopic substance in the pus of discarded surgical bandages that he called ‘NUCLEIN’ Finally in 1953, working together at the University of Cambridge in England, James Watson, an American scientist, and Francis Crick, a British researcher, made a major scientific breakthrough when they discovered the famous â€Å"double helix† – the structure of DNA, the molecule of life. In 2000 , a rough draft of a map of entire human genome was completed. In 2003,the final draft was completed . This information is being used to understand and function of disease. An interesting fact is If we unwrap all of the DNA of one individual’s body cell , we could reach the moon ! Physical Properties In living organisms such as humans, DNA exists as a pair of molecules rather than a single molecule. These strands are entwined in the shape of a double helix and the helix is kept stable by hydrogen bonds, which can be found between the bases attached to the two strands. A long polymer, DNA is made up of smaller units called nucleotides. In turn, each nucleotide consists of a phosphate group, a sugar and a nitrogenous base. two helical chains each coiled round the same axis, and each with a pitch of 34  A and a radius of 10  A According to another study, when measured in a particular solution, the DNA chain measured 22 to 26  A wide, and one nucleotide unit measured 3. 3  A (0. 33  nm) long * Base Pairing 1. Base pairing is a defining property of DNA and was particularly exciting when it was first discovered because it suggested the ‘copying' mechanism for DNA. 2. In DNA, bases are specific in that an adenine base, for example, only pairs with a thymine base. Following on that premise, a cytosine base will only bond to a guanine base. This base pairing is also known as complementary base pairing. * DNA Grooves DNA has two kinds of grooves that play important roles in its functioning. 1. Major and minor grooves are structures to allow for necessary proteins in your body to make contact with bases. You might wonder what makes it so important for proteins to attach to the bases. * DNA Supercoiling If you try to picture a rope, you can get a visual image of DNA supercoiling. 1. This coiling is a central property of DNA. DNA can be in a relaxed or coiled state and it is this coiling that allows our extremely long strands of DNA to fit or ‘pack' into the comparatively much smaller cells in our bodies. * DNA Conformations DNA can exist in different conformations and these are important for a range of DNA mechanisms. These conformations interact with enzymes in your body and are also involved in aspects such as DNA repair. * Temperature As thermal energy increases, the frequency of hydrogen bonds breaking between the molecules increases. The Tm (melting temperature) of a DNA molecule is the temperature in which half the DNA molecules are denatures * DENSITY A. Density can be measured by CsCl-density ultracentrifugation B. Density can be used to estimate G+C content C. Density studies show the existence of satellite DNA * pH pH is lower then one result in the breakage of phosphodiester bonds between nucleotides and breakage of the N-glycosidic bond between the sugar and purine bases . H of around 4 results in the selective breakage of N-glycosidic bonds between the sugar and purinesBase tends to change the polarity of groups involved in hydrogen bondsDNA is resistant to hydrolysis to about pH 13 * DENATURATION: DNA is considered denatured when the double stranded DNA molecule is converted into two single stranded molecules CHEMICAL PROPERTIES A nucleoside is made of a sugar + a nitrogenous base. A nucleotide is made of a phosphate + a sugar + a nitrogenous base. In DNA, the nucleotide is a deoxyribonucleotide (in RNA, the nucleotide is a ribonucleotide). * Phosphoric acid Gives a phosphate group. * Sugar: Deoxyribose, which is a cyclic pentose (5-carbon sugar). Note: the sugar in RNA is a ribose. Carbons in the sugar are noted from 1†² to 5†². A nitrogen atom from the nitrogenous base links to C1†² (glycosidic link), and the phosphate links to C5†² (ester link) to make the nucleotide. The nucleotide is therefore: phosphate – C5†² sugar C1†² – base. * Nitrogenous bases: Aromatic heterocycles; there are purines and pyrimidines. Purines: adenine (A) and guanine (G). – Pyrimidines: cytosine (C) and thymine (T) (Note: thymine is replaced by uracyle (U) in RNA) The backbone of the DNA strand is made from alternating phosphate and sugar residues. [10] The sugar in DNA is 2-deoxyribose, which is a pentose (five-carbon) sugar. * The sugars are joined together by phosphate groups that form phosphodies ter bonds between the third and fifth carbon atoms of adjacent sugar rings. * These asymmetric bonds mean a strand of DNA has a direction. In a double helix the direction of the nucleotides in one strand is opposite to their direction in the other strand: the strands are antiparallel. The asymmetric ends of DNA strands are called the 5? (five prime) and 3? (three prime) ends, with the 5†² end having a terminal phosphate group and the 3†² end a terminal hydroxyl group. The DNA double helix is stabilized primarily by two forces: hydrogen bonds between nucleotides & base-stacking interactions among the aromatic nucleobases Role that DNA plays in life: DNA is the blueprint of biological life from its inception to its growth and till death. Its discovery has not only revolutionized science and medicine but it has affected all walks of life; whether they are social, legal, criminal or inheritance related. DNA’s discovery has become important to the extent that it has even influenced a nation’s security parameters / concerns, as scientists have gone all the way to developing biological weapons. Genealogy:The study of ancestry, depends on the study of DNA. With the help of verbal and written history, and cues from DNA testing, one can trace his ancestors and learn about his family tree. Forensic science and its applications:DNA is an important part of it. It has resulted in many breakthroughs in criminal cases as it can be used to trace the criminals by comparing the DNA samples found on the crime scene with those extracted from the suspects. Agriculture: Scientists have used this knowledge to improve the food products and crops by genetically modifying them and making them more powerful to fight diseases. Some really Interesting information about DNA! * 99. 9% of our DNA sequence is the same as other humans. This 0. 1% DNA difference between us may have to do with the number of nucleotides in a person’s DNA! When DNA is copied into a new life , the nucleotides are either gained or lost in the process. This gain or loss results in our differences ! * It would take a person typing 60 words per minute, 8 hour a day, around 50 years to type the human genome! * Our entire DNA sequence is called a genome and there’s an estimated 3000,000,000 DNA bases in our genome! * A complete 3 billion base genome would take 3 GIGABYTES of storage space. * Our entire DNA sequence would fill 2001,000 pages! * Human and Chimps share anywhere between 94-99% of their DNA! * According to a recent research ,humans have at least 1-4% NEANDERTHAL DNA . At some point HOMOSAPIENS and NEANDERTHAL mingled and mated! References * Alberts, Bruce; Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts and Peter Walters (2002). Molecular Biology of the Cell; Fourth Edition. New York and London: Garland Science. * Wikipedia- http://en. wikipedia. org/wiki/DNA * Watson J. D. and Crick F. H. C. (1953). â€Å"A Structure for Deoxyribose Nucleic Acid† (PDF) * T. M. Devlin's Textbook of Biochemistry 7th (Seventh) edition(Textbook of Biochemistry with Clinical Correlations (Textbook of Biochemistry w/ Clinical Correlations) [Hardcover])(2010)