The Structure Of DNA Biology Essay

Deoxyribonucleic acid ( deoxyribonucleic acid ) and RNA ( ribonucleic acid ) are familial stuffs. They are chemically similar but their 3 dimensional constructions are different. Deoxyribonucleic acid is informational molecule transporting familial information in the exact sequences of its bases but RNA is a catalytic molecule. Deoxyribonucleic acid and RNA have three different conformations each, with distinguishable construction which are diversely suited for their maps. ( Freifelder et al. 1998 ) So, after reading this brochure, one can cognize about the different signifiers of DNA and RNA, how their different structural programs are ideally suited for their maps?

1.2: Structure OF Deoxyribonucleic acid:

The right construction of DNA was foremost obtained by J.D. Watson and F.H.C. Crick of Cambridge University in the twelvemonth 1953. Their double-helix theoretical account of DNA construction was based on the E. Chargaff ‘s base composing regulation. Harmonizing to Chargaff, the concentration of T ( T ) was ever equal to that of A ( A ) and the concentration of G ( G ) was ever equal to that of C ( C ) . It was merely true within the same species but was found different in the being of different species. ( Hartl et al. 2000 )

Deoxyribonucleic acid has no O atom at the 2 ‘ C. Nitrogenous bases are attached at the 1’carbon and phosphate group to the 5 ‘ C of the pentose sugar. DNA double-helix contains two polynucleotide ironss coiled one another in a coiling mode. Each polynucleotide ironss consist of sequence of bases joined together by the phosphodiester bonds. The two ironss are linked together by H-bonds to give a coiling constellation. H-bonds are formed between the purines ( Adenine & A ; Guanine ) and the pyrimidines ( Thymidine & A ; Cytosine ) . Bases in DNA are specifically paired. Adenine ( A ) of one strand is linked with Thymine ( T ) of other strand through two H-bonds and Guanine ( G ) with Cytosine ( C ) through three H-bonds. Therefore, base sequences of other strand are known through the base coupling of one strand ( specific base coupling ) . Such status is called “ complementary base coupling ” . Two strands runs antiparallel, with one strand in the 3’-5 ‘ and other in the 5’-3 ‘ way ( opposite chemical mutual opposition ) . ( Gardner et al. 2005 )

In DNA double-helix, base braces are stacked one upon another like a heap of documents with a 3.4C? spread between back-to-back base brace. ( Hartl et al. 2000 ) Bases are concealed towards interior side organizing hydrophobic nucleus and they are perpendicular to the axis of the spiral. Bases are traveling in the coiling mode around the coiling axis and each bend has ten basal braces. Each base brace is rotated through 36Es around the coiling axis relation to the following base brace. Therefore, 10 base braces make the complete bend of 360Es . The distortion of two complementary strands in DNA double-helix signifiers a minor channel ( 12C? ) and a major channel ( 22C? ) . ( Nelson et al. 2000 )

aˆ? ( B )

Fig1.1: ( A ) & A ; ( B ) : Double Coiling Structure of DNA. ( n.d )

( C )

Fig1.2: ( C ) : Complementary base coupling in DNA. Sugar phosphate anchor is on exterior. ( n.d )

1.3: Assorted signifiers of Deoxyribonucleic acid:

aˆ? B-form:

The standard theoretical account of DNA and is right handed. This conformation is shown by the Deoxyribonucleic acid in the aqueous solution of low salt concentration. It has precisely 10.4 nucleotide braces per bend. Each base is twisted to 36Es and has a diameter of 2nm. The base plane is tilted to 6Es and length of each bend measures 3.4nm. ( Freifelder et al. 1998 )

aˆ? A-form:

It is the conformation shown by Deoxyribonucleic acid in the high salt concentration solution or dehydrated province. It has wider and flatter spiral. Helix has minor and major channels. It has 11 bases per bend and each bend twisted to 33Es . ( Gardner et al. 2005 ) Each bend is 3.1nm in length. Base plane is tilted to the spiral at 20Es . ( Freifelder et al. 1998 )

aˆ? Z-form: ( Z- zigzagged way of the sugar phosphate anchor of the construction )

Turn in the left handed way. It has 12 base braces per bend and the length of bend is 4.5nm. Diameter of each bend is 1.8nm and the base plane is tilted to 7Es . ( Freifelder et al. 1998 ) B-form alteration to the Z-form and frailty versa with the aid of certain regulative protein.

1.4: Structure OF RNA:

Ribonucleic acid: ribonucleic acid has the same construction as that of DNA but non indistinguishable, RNA has ribose sugar alternatively of deoxyribose. It is non duplex but individual stranded. Uracil ( U ) is present in the topographic point of T ( T ) . The anchor in RNA is an jumping polymer of ribose and phosphate with phosphodiester bonds between 3 ‘ and 5 ‘ atoms from back-to-back ribose.

RNA signifier relatively shorter dual strand on itself, thereby organizing hairpin, root and loop constructions. Hairpins are formed by base partner offing 5-10 bases of each other. Stem-loops are formed by partner offing of those bases which are separated more than ten to several 100s bases. When these simple folding comes together, they make up a more complex construction termed as ‘pseudo knot ‘ . ( Lodish et Al. 2009 ) Double spiral formed between DNA & A ; RNA or RNA & A ; RNA has the conformation same to that of A-form DNA. Such RNA is called A-RNA or RNA-II. Double spiral of A-RNA contains 11bp per bend and each bend mensurating to 3nm in length. ( Lodish et Al. 2009 )

1.5: Bases of RNA. ( Uracil alternatively of T ) :


Adenine ( A ) . Guanine ( G ) .



Uracil ( U ) . Cytosine ( C ) .

Fig1.3: Bases of RNA. ( n.d )

1.6: Structure of RNA:

RNA molecule consists of four constituents: ribose, five C sugar, phosphate & A ; household of four heterocyclic bases.

Fig1.4: RNA construction. ( n.d )

1.7: Assorted signifiers of RNA based on their map in the protein synthesis:

aˆ? Ribosomal RNA ( rRNA ) ,

aˆ? Messenger RNA ( messenger RNA ) and

aˆ? Transfer RNA ( transfer RNA ) .


It is a individual, uninterrupted strand H-bonded back on itself, with a 5 ‘ at the start and 3 ‘ at the terminal. It contains a complex form of short two-base hit stranded roots, interspersed with odd single-stranded cringles and bubbles.

Fig1.5: Secondary construction of rRNA. ( Steven 2009 )


The messenger RNA constitutes 3-5 % of entire cellular RNA. ( n.d ) . It is ever individual stranded. Some of the common bases found in the messenger RNA are A, G, C and U. Certain sum of random gyrating occurs in it but basal coupling ne’er go on in it, as it will destruct its biological belongingss. Its base sequences are complementary to the section of Deoxyribonucleic acid from which it is transcribed. Its size is at least 100×3=300nts. ( n.d ) .

Cap is formed at 5 ‘ terminal by the condensation of guanylate residue in most eucaryotes and carnal viruses. Cap is therefore a out of use methylated construction, m7GppNmp Np ; where m7G=

7methyl guanosine cap, N= any of the 4 bases & A ; Nmp= 20 methyl ribose. ( n.d ) . It has behind its cap a non-coding part 1 ( NC1 ) composed of 10-100 bases. This part is rich in A and G residues. It does non interpret protein. Then, it has induction codon incorporating AUG in both procaryotes and eucaryotes. It besides consists of coding part incorporating 1500 bases and it can interpret protein. ( n.d ) .

Figure: messenger RNA.

Fig1.6: Structure of messenger RNA. ( n.d )

three: transfer RNA:

It is smallest of all RNA species. It contains sequence of 60-95 bases, largely 76. It has a molecular weight of 18-20kd. Secondary construction is ‘cloverleaf ‘ shaped with four changeless weaponries ( D-arm, T-arm, anti-codon arm and variable arm ) ; extra arm is present in instance of larger transfer RNA. ( n.d ) 5 ‘ end point transfer RNA is ever phosphorylated. Seven base pair root has non-Watson and Crick partner offing like G partner offing with U. Stem 3-4 and cringle of D-arm contains dihyuridine ( D ) base. Anti-codon three ( anti-codon arm ) and TYC sequence, pseudouradine ( T-arm ) are present at 5bp root. Between anti-codon and T-arm is ‘variable arm ‘ mensurating 3-21 bases in length.

This 3-D construction is formed in the solution. When ester linkage between 2 ‘ or 3’OH group of adenylic acid at the terminal of acceptor arm and COOH group of the amino acid, it gives charged aminoacyl-tRNA. ( Lodish et Al. 2009 ) L-shaped third construction formed from the cloverleaf has the acceptor arm at one terminal and anticodon arm at the other terminal.

( A ) ( B )

Fig1.7: ( A ) construction of transfer RNA and ( C ) cloverleaf construction of transfer RNA ( n.d ) .

1.8: Comparative maps of DNA and RNA as per their structural program:

Functions of Deoxyribonucleic acid:

Due to the formation of child and major channel in DNA, border atoms of single bases inside the channels are made approachable from outside the spiral. Therefore, DNA adhering proteins can read the basal sequences of duplex DNA by coming in contact with atoms either in child or major channel. ( Hartl et al. 2000 )

H-bonds are non parallel to the axis of DNA unlike alpha spiral in proteins. This belongings enables DNA to flex in order to organize a complex with adhering proteins. Protein-DNA complex occurs as atomic Deoxyribonucleic acid in eucaryotic cells. This flexing belongings of Deoxyribonucleic acid allows it to acquire dumbly packed in the chromatin.

In DNA, H-atom at 2’position of deoxyribose sugar ( OH in RNA ) histories for relatively greater stableness of the molecule. It allows DNA molecule to hive away familial information for the longer continuance. Whereas, in RNA 2′-OH group undergoes alkaline hydrolysis of phosphodiester bond at impersonal pH catalyzed by OH anion. It does non takes topographic point in Deoxyribonucleic acid.

The presence of Thymine ( T ) alternatively of Uracil ( U ) besides enables DNA for the long term stableness because of Thymine ‘s map in DNA fix. ( Lodish et Al. 2009 ) Complementary base coupling in DNA ( A=T, G=C ) form the footing for exact duplicate. This allows precise reproduction procedure to happen so, that the information stored in them is replicated right and successfully inherited by the girl cells

. Group of three bases in DNA molecule constitute familial codification which specifies amino acerb sequence in proteins. All information contained in the familial codification plays a major function in directing the cell organisation and cell metabolic maps. Sometimes bases are mispaired in DNA. This leads to the occasional mutants. An occasional mutant allows slow accretion of favourable mutants, which as a whole leads to the development of assortment of beings. ( Nelson et al. 2000 ) Certain bases are methylated in DNA molecule. Adenine & A ; C are more methylated so G & A ; T. Presence of methylated base ( like T ) suppresses the migration of section of DNA called jumping genes. Methylation of cytidine posses ‘ structural importance as it increases the inclination of that section of Deoxyribonucleic acid to take the Z-form. ( Nelson et al 2000 )

Functions of RNA and its different signifiers:

RNA is a catalytic molecule. It plays a broad scope of functions in the life cells.

Functions of rRNA:

It has folded construction like that of I±-helices & A ; I? strands of proteins but they has catalytic belongingss. Therefore, it catalyses the splicing procedure during the formation of bulk of functional messenger RNA in multicellular & A ; unicellular ( yeast, bacteria etc. ) eukaryotes. rRNA has the catalytic function in the formation of peptide bonds during protein synthesis. rRNA serves as the cardinal constituent of the ribosome protein fabricating machinery. ( Hartl et al. 2000 )

Functions of transfer RNA:

It functions as adapter molecules that decode the familial codification. ( n.d ) The anti-codon terminal of transfer RNA has nucleotide sequence complementary to the codon stand foring its amino acid. The anticodon enables tRNA to acknowledge the codon through complementary base coupling. Amino-acyl tRNA-synthase proteins formed by the reaction between 3’OH group of adenylic acid at acceptor arm & A ; COOH group of amino acid, is the true transcriber of familial codification into aminic acerb sequence. If it fails to acetylize RNA decently so it will take to amino acerb mutant. RNA has three different species viz. messenger RNA, transfer RNA & A ; rRNA. The messenger RNA carries coding information from the Deoxyribonucleic acid to the site of protein synthesis ( the ribosome ) , tRNA aid in the acknowledgment of the codons & A ; provides matching aminic acid. ( Nelson et al. 2000 )

Functions of messenger RNA:

It is used as the templet for protein synthesis. The presence of cap at 5 ‘ terminal of messenger RNA dramas critical function in acknowledgment of ribosome and besides in protection of RNAses. After polyadenylation, poly-A tail is attached to the 3 ‘ terminal of messenger RNA. It is the adhering site of proteins. These proteins shield mRNA from debasement by exonucleases. The procedure of polyadenylation is besides critical for expiration of written text, export of messenger RNA from the karyon & A ; interlingual rendition. ( n.d )

1.9: Mentions:

aˆ? Hartl, D.L. & A ; Jones, E.W. ( 2000 ) Genetics: Analysis of cistrons & A ; genomes. ( fifth Ed. ) USA: Jones & A ; Bartlett Publishers.

aˆ? Lodish, H. , ( 2008 ) . Molecular Cell Biology. ( 6th Ed. ) New York: W.H.Freeman & A ; Company.

aˆ? Malacinski, G.M. & A ; Freifelder, D. ( 1998 ) . Necessities of Molecular Biology. ( 3rd Ed. ) USA: Jones & A ; Bartlett Publishers.

aˆ? Nelson, D.L. & A ; Cox, M.M. ( 2000 ) . Principle of Biochemistry. ( 3rd Ed. ) U.K: Deserving Publisher.

aˆ? Gardner, E.J. , Simmons, M.J. & A ; Snustad, D.P. ( 2005 ) Principles of Genetics. ( 8th Ed. )

Singapore: John Wiley and Sons, INC.

aˆ? Structure of RNA. ( n.d ) . Retrieved on 24th March 2010, from http//

aˆ? Double coiling construction of DNA. ( n.d ) . Retrieved on 24th March 2010, from hypertext transfer protocol: // .

aˆ? Complementary base coupling in DNA. ( n.d ) . Retrieved on 24th March 2010, from hypertext transfer protocol: //

aˆ? Steven, M.C. ( 2OO9 ) . Structure of rRNA. Retrieved on 27th March 2010, from hypertext transfer protocol: // fr=yhs-avg & amp ; type=yahoo_avg_hs2-tb-web_aa & A ; p=structure % 20of % 20rRNA. Structure of messenger RNA. ( n.d ) . Retrieved on 1st April 2010, from hypertext transfer protocol: // hl=en & A ; source=hp & A ; q=STRUCTURE+OF+mRNA & A ; aq=o & A ; aqi=g10 & A ; aql= & A ; oq= & A ; gs_rfai= ) .

aˆ? Structure of messenger RNA. ( n.d ) . Retrieved on 1st April 2010, from hypertext transfer protocol: // MRNA_Structure.svg.

aˆ? Structure of transfer RNA. ( n.d ) . Retrieved on 2nd April 2010, from hypertext transfer protocol: //

Subjects ( Question )

Page no.





Structure of DNA.



Assorted signifiers of Deoxyribonucleic acid.



Structure of RNA



Assorted signifiers of RNA



Comparative maps of DNA and RNA

Functions of Deoxyribonucleic acid


Functions of RNA