structure and function of nucleic acids pdf

Structure And Function Of Nucleic Acids Pdf

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In this section, we will examine the structures of DNA and RNA, and how these structures are related to the functions these molecules perform. We will begin with DNA, which is the hereditary information in every cell, that is copied and passed on from generation to generation. The race to elucidate the structure of DNA was one of the greatest stories of 20th century science.

DNA and RNA are nucleic acids that carry out cellular processes, especially the regulation and expression of genes.

The structure, function and reactions of nucleic acids are central to molecular biology and are crucial for the understanding of complex biological processes involved. Written by leading experts, with extensive teaching experience, this new edition provides some updated and expanded coverage of nucleic acid chemistry, reactions and interactions with proteins and drugs. A brief history of the discovery of nucleic acids is followed by a molecularly based introduction to the structure and biological roles of DNA and RNA.

Nucleic acid

Last reviewed: November An acidic, chainlike biological macromolecule consisting of multiple repeated units of phosphoric acid, sugar, and purine and pyrimidine bases. Nucleic acids Fig. Each DNA strand is a long polymeric molecule consisting of many individual nucleotides linked end to end. The great size and complexity of DNAs are indicated by their molecular weights, which commonly range in the hundreds of millions. DNA is the chemical constituent of the genes of an organism; thus, it is the ultimate biochemical object of the study of genetics.

Information is contained in the DNA in the form of the sequence of nucleotide building blocks in the nucleic acid chain. See also: Gene ; Genetics. The number of nucleotide building blocks in DNA is relatively small—only four nucleotides constitute the vast majority of DNA polymeric units.

These are deoxyadenylic, deoxyguanylic, deoxycytidylic, and deoxythymidylic acids. For purposes of brevity, these nucleotides are symbolized by the letters A, G, C, and T, respectively. Each of these nucleotides consists of three fundamental chemical groups: a phosphoric acid group, a deoxyribose 5-carbon sugar group, and a nitrogenous base that is a derivative of either a purine adenine or guanine or a pyrimidine cytosine or thymine [ Fig.

See also: Nucleotide. These are the only major bases found in most DNA; however, in specific sequences, certain methylated derivatives of these bases can be detected as well. In each nucleotide, the subunits are linked together in the following order: purine or pyrimidine base—ribose sugar—phosphoric acid. Removal of the phosphoric acid group leaves a base-sugar compound, which is called a nucleoside.

The nucleosides and nucleotides are named for the base that they contain see table. It is necessary to denote the position of the phosphoric acid residue when describing nucleotides. The Watson-Crick model attributes these ratios to the phenomenon of base pairing, in which each purine base on one strand of DNA is hydrogen-bonded to a complementary pyrimidine base in an opposing DNA strand. DNA can assume a structure called the B form, which is a right-handed helical configuration resembling a coiled spring.

The strands wind about each other, with their sugar-phosphate chains forming the coil of the helix and with their bases extending inward toward the axis of the helix. The configuration of the bases allows hydrogen bonding between opposing purines and pyrimidines. Each of the base pairs lies in a plane at approximately right angles to the helix axis, forming a stack with the two sugar-phosphate chains coiled around the outside of the stack.

In addition, DNA can exist in helical structures other than the B form. One configuration, termed the Z form, is a left-handed helical structure. The Z form can exist in DNA sequences with alternating guanine and cytosine bases and may be functional in localized DNA regions; however, the B form is thought to predominate in most biological systems. The sequence of nucleotide pairs in the DNA determines all of the hereditary characteristics of any given organism.

The RNA, in turn, serves as a template in a process by which its encoded information is translated to determine the amino acid sequences of proteins. Each amino acid in a protein chain is specified by a triplet of nucleotides in RNA or nucleotide pairs in DNA known as a codon.

The set of correlations between the amino acids and their specifying codons is called the genetic code. Each gene that codes for a protein thus contains a sequence of triplet codons that corresponds to the sequence of amino acids in the polypeptide.

This sequence of codons may be interrupted by intervening DNA sequences so that the entire coding sequence is not continuous.

In addition to coding sequences, there also exist regulatory sequences, which include promoter and operator sequences involved in initiating gene transcription and terminator sequences involved in stopping transcription. Regulatory sequences are not necessarily made up of triplets, as are the codons. In order to study the regulation of a given gene, it is necessary to determine its nucleotide sequence.

See also: Amino acid ; Genetic code ; Protein ; Transcription. In every living cell, as well as in certain viruses and subcellular organelles, the function of DNA is similar; that is, it encodes genetic information and replicates to pass this information to subsequent generations. The nucleotide sequence of DNA in each organism determines the nature and number of proteins to be synthesized, as well as the organization of the protein-synthesizing apparatus.

The entire process of gene expression, by which the flow of information proceeds from DNA to RNA to protein, remains one of the most fertile areas of molecular biological research. The primary chemical difference between RNA and DNA is in the structure of the ribose sugar of the individual nucleotide building blocks. Another major chemical difference between RNA and DNA is the substitution of uridylic acid, which contains the base uracil 2,6-dioxypyrimidine for thymidylic acid as one of the four nucleotide building blocks.

Thus, incorporation of radioactive uridine can be used as a specific measure of RNA synthesis in cells, whereas incorporation of radioactive thymidine can be used as a measure of DNA synthesis. Further modifications of RNA structure exist, such as the attachment of various chemical groups for example, isopentenyl and sulfhydryl groups to purine and pyrimidine rings, methylation of the sugars, and folding and base pairing of sections of a single RNA strand to form regions of secondary structure.

Unlike DNA, nearly all RNA in cells is single-stranded except for regions of secondary structure and does not consist of double-helical duplex molecules. Another distinguishing characteristic of RNA is its alkaline lability. In contrast, DNA is stable to alkali. This class comprises those molecular species that form part of the structure of ribosomes, which are components of the protein-synthesizing machinery in the cell cytoplasm.

See also: Ribosomes. Messenger RNAs are those species that code for proteins. They are transcribed from specific genes in the cell nucleus, and they carry the genetic information to the cytoplasm, where their sequences are translated to determine amino acid sequences during the process of protein synthesis. The messenger RNAs thus consist primarily of triplet codons. Most messenger RNAs are derived from longer precursor molecules that are the primary products of transcription and that are found in the nucleus.

These precursors undergo several steps known as RNA processing, eventually resulting in production of cytoplasmic messenger molecules ready for translation. See also: Cell nucleus. Transfer RNAs are small RNA molecules that possess a relatively high proportion of modified and unusual bases, such as methylinosine or pseudouridine. Each transfer RNA molecule possesses an anticodon and an amino acid—binding site. The anticodon is a triplet complementary to the messenger RNA codon for a particular amino acid.

A transfer RNA molecule bound to its particular amino acid is termed charged. The charged transfer RNAs participate in protein synthesis; through base pairing, they bind to each appropriate codon in a messenger RNA molecule and thus order the sequence of attached amino acids for polymerization. As in DNA replication, base pairing orders the sequence of nucleotides during transcription. In RNA synthesis, uridine rather than thymidine base-pairs with adenine. The primary biological role of RNA is to direct the process of protein synthesis.

The three major RNA classes perform different specialized functions toward this end. The completed ribosome serves as a minifactory where all the components of protein synthesis are brought together during translation of the messenger RNA.

The messenger RNA binds to the ribosome at a point near the initiation codon for protein synthesis. Through codon-anticodon base pairing between messenger and transfer RNA sequences, the transfer RNA molecules bearing amino acids are juxtaposed to allow formation of the first peptide bond between amino acids.

Then, the ribosome moves along the messenger RNA strand as more amino acids are added to the peptide chain. RNA of certain bacterial viruses serves a dual function. In certain bacteriophages viruses that infect bacterial cells , the RNA serves as a message to direct synthesis of viral-coat proteins and of enzymes needed for viral replication.

The RNA also serves as a template for viral replication. These enzymes first produce an intermediate replicative form of the viral RNA that consists of complementary RNA strands.

One of these strands then serves as the sense strand for synthesis of multiple copies of the original viral RNA. See also: Bacteriophage ; Enzyme ; Virus. RNA also serves as the actively transmitted genomic agent of certain viruses that infect cells of higher organisms.

For example, Rous sarcoma virus, which is an avian tumor virus, contains RNA as its nucleic acid component. The viral DNA is then incorporated into the host cell genome, where it codes for enzymes that are involved in altering normal cell processes.

These enzymes, as well as the site at which the virus integrates, regulate the drastic transformation of cell functions, inducing cell division and the ultimate formation of a tumor.

See also: Reverse transcriptase ; Rous sarcoma ; Tumor viruses. To learn more about subscribing to AccessScience, or to request a no-risk trial of this award-winning scientific reference for your institution, fill in your information and a member of our Sales Team will contact you as soon as possible.

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Key Concepts Hide A nucleic acid is an acidic, chainlike biological macromolecule consisting of multiple repeated units of phosphoric acid, sugar, and purine and pyrimidine bases. Nucleic acids are involved in the preservation, replication, and expression of hereditary information in every living cell.

DNA is the chemical constituent of the genes of an organism. The structure of a nucleotide, consisting of a phosphate group, sugar, and nitrogenous base, is shown at the top left. The structure of a nucleic acid, which consists of repeating units of nucleotides connected by phosphodiester bonds, is shown at the bottom right.

Deoxyribonucleic acid Each DNA strand is a long polymeric molecule consisting of many individual nucleotides linked end to end.

See also: Nucleotide Fig. Guanine-to-cytosine binding and adenine-to-thymine binding are also shown. Sequences The sequence of nucleotide pairs in the DNA determines all of the hereditary characteristics of any given organism. Function In every living cell, as well as in certain viruses and subcellular organelles, the function of DNA is similar; that is, it encodes genetic information and replicates to pass this information to subsequent generations. Function The primary biological role of RNA is to direct the process of protein synthesis.

See also: Bacteriophage ; Enzyme ; Virus RNA also serves as the actively transmitted genomic agent of certain viruses that infect cells of higher organisms. You may already have access to this content. Sign In. Get AccessScience for your institution. Subscribe To learn more about subscribing to AccessScience, or to request a no-risk trial of this award-winning scientific reference for your institution, fill in your information and a member of our Sales Team will contact you as soon as possible.

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2.6: Structure and Function - Nucleic Acids

Steve Minchin, Julia Lodge; Understanding biochemistry: structure and function of nucleic acids. Essays Biochem 16 October ; 63 4 : — Nucleic acids, deoxyribonucleic acid DNA and ribonucleic acid RNA , carry genetic information which is read in cells to make the RNA and proteins by which living things function. The well-known structure of the DNA double helix allows this information to be copied and passed on to the next generation. In this article we summarise the structure and function of nucleic acids.


Because a nucleic acid is a polymer of many nucleotide molecules, DNA and RNA molecules are called polynucleotides. The structure of a polynucleotide is.


Nucleic acid

Nucleic acid , naturally occurring chemical compound that is capable of being broken down to yield phosphoric acid , sugars, and a mixture of organic bases purines and pyrimidines. Nucleic acids are the main information-carrying molecules of the cell , and, by directing the process of protein synthesis , they determine the inherited characteristics of every living thing. DNA is the master blueprint for life and constitutes the genetic material in all free-living organisms and most viruses.

Structure and Dynamics of Biopolymers pp Cite as. The biological functions of nucleic acids depend on their conformations; we will discuss one example: the mechanism of mutation in DNA. A mutation occurs when a base pair in DNA is substituted for another one, or when one or more base pairs are added or deleted. A base pair substitution can change one amino acid into another, it can change an amino acid into a stop signal which aborts protein synthesis, it can affect the control of replication, transcription or translation, or it can be a silent mutation which has no apparent effect.

Nucleic acids are the biopolymers , or large biomolecules , essential to all known forms of life. They are composed of nucleotides , which are the monomers made of three components: a 5-carbon sugar , a phosphate group and a nitrogenous base.

Understanding biochemistry: structure and function of nucleic acids

Last reviewed: November An acidic, chainlike biological macromolecule consisting of multiple repeated units of phosphoric acid, sugar, and purine and pyrimidine bases. Nucleic acids Fig. Each DNA strand is a long polymeric molecule consisting of many individual nucleotides linked end to end. The great size and complexity of DNAs are indicated by their molecular weights, which commonly range in the hundreds of millions.

Nucleic acids, deoxyribonucleic acid DNA and ribonucleic acid RNA , carry genetic information which is read in cells to make the RNA and proteins by which living things function. The well-known structure of the DNA double helix allows this information to be copied and passed on to the next generation. In this article we summarise the structure and function of nucleic acids. The article includes a historical perspective and summarises some of the early work which led to our understanding of this important molecule and how it functions; many of these pioneering scientists were awarded Nobel Prizes for their work. We explain the structure of the DNA molecule, how it is packaged into chromosomes and how it is replicated prior to cell division.


Nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), carry genetic information which is read in cells to make the RNA and proteins by which living things function. The well-known structure of the DNA double helix allows this information to be copied and passed on to the next generation.


Structure and Function in Nucleic Acids: Mutagenesis

Supplementary files

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Рухнул не только его план пристроить черный ход к Цифровой крепости. В результате его легкомыслия АНБ оказалось на пороге крупнейшего в истории краха, краха в сфере национальной безопасности Соединенных Штатов. - Коммандер, вы ни в чем не виноваты! - воскликнула.  - Если бы Танкадо был жив, мы могли бы заключить с ним сделку, и у нас был бы выбор. Но Стратмор ее не слышал.

Танкадо отдал кольцо.

Он с трудом открыл глаза и увидел первые солнечные лучи. Беккер прекрасно помнил все, что произошло, и опустил глаза, думая увидеть перед собой своего убийцу. Но того человека в очках нигде не. Были другие люди.

 - Я хочу быть абсолютно уверен, что это абсолютно стойкий шифр.

Сьюзан была убеждена, что это невозможно. Угрожающий потенциал всей этой ситуации подавил. Какие вообще у них есть доказательства, что Танкадо действительно создал Цифровую крепость. Только его собственные утверждения в электронных посланиях.

Может быть, Танкадо защитил его ровно настолько, чтобы вы на него наткнулись и сочли, что вам очень повезло. Это придает правдоподобность его электронной переписке. - Тебе следовало бы работать в полиции, - улыбнулся Стратмор.

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