![4
the cell can maintain itself, grow, create offspring and perform any specialized
functions it's meant to do. Nucleic acids thus control the information that makes
every cell, and every organism, what it is.
Nucleic acids were discovered by Friedrich Miescher in 1869.
Experimental studies of nucleic acids constitute a major part of modern
biological and medical research, and form a foundation for genome and forensic
science, as well as the biotechnology and pharmaceutical industries.
[The Swiss scientist Friedrich Miescher discovered nucleic acids (DNA) in 1869.
Later, he raises the idea that they could be involved in heredity]
In the 1920's nucleic acids were found to be major components of
chromosomes, small gene-carrying bodies in the nuclei of complex cells.
Elemental analysis of nucleic acids showed the presence of phosphorus, in
addition to the usual C, H, and N & O. Unlike proteins, nucleic acids contained
no sulphur. Complete hydrolysis of chromosomal nucleic acids gave inorganic
phosphate, 2-deoxyribose (a previously unknown sugar) and four different
heterocyclic bases. To reflect the unusual sugar component, chromosomal
nucleic acids are called deoxyribonucleic acids, abbreviated DNA. Analogous
nucleic acids in which the sugar component is ribose are termed ribonucleic
acids, abbreviated RNA. The acidic character of the nucleic acids was attributed
to the phosphoric acid moiety.](https://image.slidesharecdn.com/assignment-140920092118-phpapp01/85/Biological-functions-of-Nucleic-Acids-4-320.jpg)
Biological functions of Nucleic Acids
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- 3. 3 SL.NO CONTENTS PAGE NO 1. 2. 3. 4. 5. 6. 7. NUCLEIC ACIDS MUTATIONS OF NUCLEIC ACIDS EXAMPLES OF NUCLEIC ACIDS COMPONENTS OF NUCLEIC ACIDS ARTIFICIAL NUCLEIC ACID ANALOGS BIOLOGICAL FUNCTIONS OF NUCLEIC ACIDS REFERENCE 4 – 5 5 – 6 6 – 7 7 – 10 10 11– 12 13 NUCLEIC ACIDS Nucleic acids are large macromolecules composed of smaller nucleotides. These nucleotides are made up of two backbones that alternate between sugar groups and phosphate molecules (the phosphate makes it slightly acidic). Extending from both sides of these sugar groups are two nucleotide bases that bond to each other. These bonding patterns give rise to the double helix shape that we are familiar with. Nucleic acids are vital for cell functioning, and therefore for life. There are two types of nucleic acids, DNA and RNA. Together, they keep track of hereditary information in a cell so that
- 4. 4 the cell can maintain itself, grow, create offspring and perform any specialized functions it's meant to do. Nucleic acids thus control the information that makes every cell, and every organism, what it is. Nucleic acids were discovered by Friedrich Miescher in 1869. Experimental studies of nucleic acids constitute a major part of modern biological and medical research, and form a foundation for genome and forensic science, as well as the biotechnology and pharmaceutical industries. [The Swiss scientist Friedrich Miescher discovered nucleic acids (DNA) in 1869. Later, he raises the idea that they could be involved in heredity] In the 1920's nucleic acids were found to be major components of chromosomes, small gene-carrying bodies in the nuclei of complex cells. Elemental analysis of nucleic acids showed the presence of phosphorus, in addition to the usual C, H, and N & O. Unlike proteins, nucleic acids contained no sulphur. Complete hydrolysis of chromosomal nucleic acids gave inorganic phosphate, 2-deoxyribose (a previously unknown sugar) and four different heterocyclic bases. To reflect the unusual sugar component, chromosomal nucleic acids are called deoxyribonucleic acids, abbreviated DNA. Analogous nucleic acids in which the sugar component is ribose are termed ribonucleic acids, abbreviated RNA. The acidic character of the nucleic acids was attributed to the phosphoric acid moiety.
- 5. 5 Mutations of Nucleic Acids While nucleic acids can do so much good for the body, mutation can result in debilitating or life threatening diseases. There is a long list of genetics conditions caused by mutations involving nucleic acids. Some of the more prominent conditions caused by mutations of nucleic acids like DNA and RNA include: Diseases of the heart and muscle Some DNA mutations in mitochondria have been linked to diseases of the heart and muscles. When there is damage to the mitochondrial DNA, tissues and organs can begin to deteriorate causing painful and sometimes fatal conditions. Breast cancer Mutations of the genes BRCA1 and BRCA2 have been linked to causing breast cancer. This determination, in the 1990’s, has lead to increased research regarding these genes and their mutations in an effort to reduce the risk of acquiring breast cancer. Ovarian Cancer The same genes that were determined to cause breast cancer upon mutation have also been linked to ovarian cancer. Researchers are still working to determine how these mutations happen and how to prevent them.
- 6. 6 Down Syndrome Down syndrome is another condition that is caused by a mutation of a gene in the DNA. In the past several decades, great strides have been made in medicine in understanding and diagnosing Down syndrome. Color Blindness While certainly not as debilitating as some other genetic diseases, color blindness is also a result of mutation of genes on DNA. This condition is more prevalent in men and exists when one is unable to distinguish between colors or to see colors in typical lighting. Examples of Nucleic Acids Nucleic acids, best-known as DNA and RNA, are often termed "the building blocks of life." These building blocks are found in the nuclei of cells and help proteins to be built, help cells to replicate, govern heredity and the cell's chemical processes. Nucleic acids are made up of five pieces, or monomers, including: Guanine Cytosine Thymine Cytosine Uracil These acids are the stores and transmitters of cellular information in the body.
- 7. 7 DNA Deoxyribonucleic acid is the most common form. Its base pairs are adenine (A), thymine (T), guanine (G) and cytosine (C). There are small differences between them. For instance, A and G have a double ring structure, which allows them to bind to a single ring structure. A binds with T, and G binds with C. When DNA is replicated, its structure unwinds, splitting the hydrogen bonds of the bases in half. Complimentary bases are then formed. This is similar in concept to the way in which DNA is read. The polymeric structure of DNA may be described in terms of monomeric units of increasing complexity. In the top shaded box of the following illustration, the three relatively simple components mentioned earlier are shown. Below that on the left, formulas for phosphoric acid and a nucleoside are drawn. Condensation polymerization of these leads to the DNA formulation outlined above. Finally, a 5'- monophosphate ester, called a nucleotide may be drawn as a single monomer unit, shown in the shaded box to
- 8. 8 the right. Since a monophosphate ester of this kind is a strong acid (pKa of 1.0), it will be fully ionized at the usual physiological pH (ca.7.4). Names for these DNA components are given in the table to the right of the diagram. Isomeric 3'-monophospate nucleotides are also known, and both isomers are found in cells. They may be obtained by selective hydrolysis of DNA through the action of nuclease enzymes. Anhydride-like di- and tri-phosphate nucleotides have been identified as important energy carriers in biochemical reactions, the most common being ATP (adenosine 5'- triphosphate). RNA
- 9. 9 Another kind of nucleic acid is ribonucleic acid, which is similar in structure to DNA but instead supplements uracil (U) for thymine. RNA is used exclusively in viruses and perhaps even the earliest forms of life, but in most modern life RNA has another critical function. It translates genetic information to proteins, which help facilitate important functions of the cell.The high molecular weight nucleic acid, DNA, are found chiefly in the nuclei of complex cells, known as eukaryotic cells, or in the nucleoid regions of prokaryotic cells, such as bacteria. It is often associated with proteins that help to pack it in a usable fashion. Ribonucleic acid (RNA) functions in converting genetic information from genes into the amino acid sequences of proteins. The three universal types of RNA include transfer RNA (tRNA), messenger RNA (mRNA), and ribosomal RNA (rRNA). Messenger RNA acts to carry genetic sequence information between DNA and ribosomes, directing protein synthesis. Ribosomal RNA is a major component of the ribosome, and catalyzes peptide bond formation. Transfer RNA serves as the carrier molecule for amino acids to be used in protein synthesis, and is responsible for decoding the mRNA. In addition, many other classes of RNA are now known. In contrast, a lower molecular weight, but much more abundant nucleic acid, RNA, is distributed throughout the cell, most commonly in small numerous organelles called ribosomes. Three kinds of RNA are identified, the largest subgroup (85 to 90%) being ribosomal RNA, rRNA, the major component of ribosomes, together with proteins. The size of rRNA molecules varies, but is generally less than a thousandth the size of DNA. The other forms of RNA are messenger RNA, mRNA, and transfer RNA, tRNA. Both have a more transient existence and are smaller than rRNA. All these RNA's have similar constitutions, and differ from DNA in two important respects. As shown in the following diagram, the sugar component of RNA is ribose, and the pyrimidine base uracil replaces the thymine base of DNA. The RNA's play a vital role in the transfer of information (transcription) from the DNA library to the protein factories called ribosomes, and in the interpretation of that information (translation) for the synthesis of specific polypeptides.
- 10. 10 Artificial nucleic acid analogs Artificial nucleic acid analogs have been designed and synthesized by chemists, and include peptide nucleic acid, morpholino- and locked nucleic acid, as well as glycol nucleic acid and threose nucleic acid. Each of these is distinguished from naturally occurring DNA or RNA by changes to the backbone of the molecule. Nucleic Acid Functions The human body is made up of millions of cells that work to maintain the body's overall system and function. Each cell, in turn, has its own set of processes designed to carry out necessary cell functions. Nucleic acid plays an essential role in coordinating and maintaining individual cell processes throughout the body.
- 11. 11 BIOLOGICAL FUNCTIONS OF NUCLEIC ACIDS 1. Replication : Process by which a single DNA molecule produces two identical copies of itself is called replication. Replication of DNA is an enzyme catalysed process. In this process, two strands of DNA helix unwind and each strand serves as a template or pattern for the synthesis of a new strand. Newly synthesized complementary strand is an exact copy of the original DNA. In this way hereditary characteristics are transmitted from one cell to another.
- 12. 12 i) Transcription : It is the process of synthesis of RNA (mRNA) by using DNA as template. This process is similar to replication process. Differ in following ways. In transcription, ribose nucleotide assemble along the uncoiled template instead of deoxyribose nucleotide and base uracil (U) is substituted for the base thymine (T). Synthesis of RNA or DNA always takes place in 5' - 3' direction. Process is catalysed by an enzyme RNA polymerase. In this way DNA transfers its genetic code to mRNA. After synthesis, RNA detaches from DNA and moves from nucleus to the cytoplasm where it acts as template for protein synthesis. DNA returns to its double helix structure. (ii) Translation : It is the process of synthesis of protein. This process is directed by mRNA in the cytoplasm of cell with the help of tRNA (transfer RNA) and ribosomal particles (RNA – protein complex).The process occurs with the attachment of mRNA to ribosome particle mRNA then gives the message of the DNA and dictates the specific amino acid sequence for the synthesis of protein. 4 bases in mRNA act in the form of triplets and each triplet acts as a code for a particular amino acid. This triplet is called codon. There may be more than one codon for same amino acid. E.g. amino acid methionine has
- 13. 13 code AUG while glycine has 4 codons GGU, GGC, GGA, GGG. These codon expressed in mRNA is read by tRNA carrying anticodon and is translated into an amino acid sequence. This process is repeated again and again thus proteins are synthesized. After completion, it is released from ribosome. Protein synthesis : It is a fast process and about 20 amino acids are added in one second. It may be noted that translation is always unidirectional but transcription can sometimes be reversed. (RNA is copies into DNA) This is called reverse transcription (occurs in Retroviruses). Genetic Code Segment of DNA is called gene and each triplet of nucleotides is called a codon that specifies one amino acid. This relationship between nucleotide triplets and amino acids is called genetic code. E.g.
- 14. 14 Reference : Wolfram Saenger, Principles of Nucleic Acid Structure, 1984, Springer-Verlag New York Inc. Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter Molecular Biology of the Cell, 2007, ISBN 978-0-8153-4105-5. Fourth edition is available online through the NCBI Bookshelf: Jeremy M Berg, John L Tymoczko, and Lubert Stryer, Biochemistry 5th edition, 2002, W H Freeman. Available online through the NCBI Bookshelf: link Astrid Sigel, Helmut Sigel and Roland K. O. Sigel, ed. (2012). Interplay between Metal Ions and Nucleic Acids. Metal Ions in Life Sciences 10. Springer. doi:10.1007/978-94-007-2172-2. ISBN 978-94- 007-2171-5. Sanger, Frederick. 1980. Determination of Nucleotide Sequences in DNA.http://nobelprize.org/nobel_prizes/chemistry/laureates/1980/san ger-lecture.html