Deoxyribonucleic acid and RNA are the molecular signifiers of familial information. The construction of every protein and every biomolecule are the consequences of information passed on from the nucleotide sequence of nucleic acids. Information for the construction of a polypeptide concatenation is stored in a polynucleotide concatenation of DNA. Sequence of bases in a peculiar section of DNA will find the sequence of aminic acids in a polypeptide concatenation. Information from Deoxyribonucleic acid is transferred to RNA and from RNA to protein synthesising machinery ( Central Dogma ) . ( Lewin, 1985 )
Therefore, the nucleic acids have complex and diverse constructions that make them ideally suited for the assorted maps that have to be carried out.
Double spiral construction of Deoxyribonucleic acid
Deoxyribonucleic acid is formed by two antiparallel polynucleotide ironss, which are coiled in a coiling construction around a cardinal axis. The antiparallel strands give rise to a right-handed dual spiral. The anchors, which are formed by jumping deoxyribose and phosphate group, face the exterior of the dual spiral towards the aqueous environment organizing the hydrophilic portion of the DNA. The side concatenation consisting of purine and pyrimidine bases are enclosed inside organizing the hydrophilic part of the dual spiral
The bases of each construction are about two-dimensional and perpendicular to the axis of dual spiral. A base of one strand pairs with the base of other strand, which are in the same plane harmonizing to the complementarity ( adenine and T, C and G ) . Two H-bond are formed between A and T and three between G and C. ( this is the ground for the trouble in separation the two strands ) . Stability of the dual spiral is due to
H-bonds between the bases
Vander Waals interactions between the stacked bases. The bases on the inside are stacked upon the other like the stacking of coins.
The dual spiral makes a complete bend every 34 A, has a diameter of about 20A. The distance between two bases is 3.4 A, hence there are 10 bases per complete bend. Each base brace is rotated 360 around the axis relation to the following base brace. The dual spiral has a narrow grove of diameter of 12A and a broad channel with a diameter of 22A. ( Beginning: Weil, 1996 )
Fig. Watson – Crick Model for the construction of dual spiral Deoxyribonucleic acid
( Beginning: Kratz, 2009 )
Structure of RNA
RNA is formed of individual stranded polypeptide concatenation, which consists of a phosphorylated pentose as the anchor and bases as side ironss, which are either purine or pyrimidine. The bases are adenine, G, C, and U. The polynucleotide concatenation tallies from 5 ‘ C to 3 ‘ C. The bases are connected by phosphodiester bond between 5 ‘ C and 3 ‘ C of the sugar. The bases are linked to the 1 ‘ C of the sugar by N-glycosidic linkage. The sugar is a ribose ( OH at the 2 C of the pentose ) . ( Beginning: Alberts etal, 2008 )
Figure: A: primary construction of RNA. Bacillus: secondary construction of RNA.
( Beginning: RNA construction, n.d )
Similarities in construction between DNA and RNA.
The primary construction of DNA and RNA are about same because both are holding their monomers as bases, which give rise to polynucleotide ironss.
Deoxyribonucleic acid has several hundred 1000000s of bases. RNA has fewer with merely 10s to 1000s of bases. A nucleotide consist of
A phosphate group attached to 5’carbon of sugar
A base attached to the 1’C of the sugar through N-glycosidic linkage
The anchor of the polynucleotide concatenation is formed by jumping units of sugar and phosphate group. Two sugars are linked together by phosphodiester linkage. The bases are attached as side ironss to 1’Carbon through N-glycosidic linkage. In DNA the sugar is a deoxyribose whereas in RNA, the sugar is a ribose.
In nucleic acids, the bases attached to the 1 ‘ Carbon of the sugar is of five types. They are adenine and G jointly called purine and C, T and U jointly called pyrimidine. Purines are formed of dual ring and the pyrimidines are formed of individual ring.
( Beginning: Lodish et Al, 2004 )
Fig. the nitrogen-bearing bases
( Beginning: Kratz, 2009 )
Adenine, G and C are found in both DNA and RNA. Thymine is found merely in DNA and U is found merely in RNA. The 5 ‘ terminus of polynucleotide concatenation has a hydroxyl or phosphate group while the 3 ‘ terminal ends up at hydroxyl group on the 3 ‘ Carbon of the terminal sugar.
Fig. polynucleotide concatenation of DNA and RNA
( Beginning: Polynucleotide concatenation of DNA and RNA, n.d )
Functions of Deoxyribonucleic acid
Using the parental dual strand, girl strands are produced. The parental strands are separated ( semi conservative ) or non separated ( conservative ) and so used as templet for synthesis of girl strands.
Sometimes the base sequence can alter and undergo mutant harmonizing to alteration in the environment in order to be compatible to that changed environment.
Since the strands are complementary to each other girl strands formed are besides complementary to rear strands and hence there is less opportunity of misinterpreting the information.
Due to the H bonds between the bases and base stacking, the dual spiral is really hard to divide. Unlike RNA, DNA has no OH at 2’carbon of the sugar, which makes it less apt to hydrolysis at normal temperature. Thymine that has a methyl group protects the Deoxyribonucleic acid from denaturing enzymes. ( Beginning: Sharma, N.B, 2010 )
Presence of T makes DNA impersonal due to presence of methyl group. Thymine besides repairs Deoxyribonucleic acid by deaminization of C to uracil. ( Beginning: Becker et Al, 2006 )
Functions of RNA
Due to the presence of OH group at 2 ‘ C of the sugar in RNA, it is more likely to be unstable. The OH group makes it more reactive. If exposed to alkaline solution, RNA can be broken down into mononucleotides. Due to this ground, RNA can execute many specific maps in the cell.
RNA is individual stranded unlike DNA, which is dual stranded. Single stranded nature enables flexibleness to establish brace within itself between different parts and fold into many secondary constructions like hairpins, root cringles and pseudo knots to transport its diverse maps. ( Beginning: Lodish et Al, 2004 )
Presence of uracil makes RNA really reactive due to the absence of methyl group in U and this enables RNA to transport out diverse maps in protein synthesis.
( Beginning: Becker etal, 2006 )
Some RNAs are catalytic in map and are called ribozymes. Ribozymes catalyze a procedure called splice where there is cutting and remotion of the noncoding DNAs and ligation of coding DNAs. Some RNAs can undergo self splice. ( Beginning: Nelson and Cox, 2003 )
Three types of RNA
RNA is of three types.
T RNA ( Structure and map )
In transportation RNA the sequence of bases forms the primary construction. tRNA comprises of approximately 40 to 90 bases and weigh around 30000. The secondary construction of transfer RNA is called “ cloverleaf ” . The cloverleaf conformation is maintained by little parts, which are complementary. The cloverleaf has four weaponries that are named harmonizing to their construction and maps. They are:
The acceptor arm: Present at the top and here the bases are paired but CCA at the 3` terminal are odd and exceeds beyond 5` terminal.
D arm ( dihydrouracil cringle ) : Present at the left side and named so due to the presence of modified uracil base dihydrouridine.
T I? C arm: Present at the right side and is named so due to the presence of these three sequences. ( Beginning: Nelson and Cox, 2000 )
Anticodon arm: Present at the underside and is named for the presence of anticodon at its tip.
Excess arm or variable cringle: Present between the T I? C arm and the anticodon.
( Beginning: Lewin, 1985 )
Harmonizing to Weaver in 2002, the cloverleaf merely explains the base coupling form. The true 3-dimensional construction is inverted L.
Figure: The cloverleaf construction
Figure: The cloverleaf construction
( Beginning: The cloverleaf, n.d )
The chief map of transfer RNA is basal coupling. The transfer RNA with the aid of enzyme amino acyl transfer RNA synthetase carries merely specific amino acids, which correspond to it. At the base of cloverleaf, the codon nowadays is anticodon, which reads the codon of messenger RNA. This is catalyzed by amino acyl T RNA synthetase. Therefore, aminic acids are incorporated into right proteins.
( Beginning: Weaver, 2002 )
The acceptor weaponries covalently bonds to peculiar amino acids and this is called bear downing. It is regulated by enzyme amino acyl T RNA synthetase.
( Beginning: Weaver, 2002 )
3. messenger RNA ( construction and map )
The size of messenger RNA is really much variable because the proteins translated by messenger RNAs are of different sizes. A polycistromic messenger RNA can be 3 times longer than the largest ribosomal RNA since it can hold approximately 104 bases. It can be approximately 120 times longer than a transfer RNA and weigh 3.5×106. Monocistronic messenger RNA length is limitless to the coding part between the induction codon ( AUG ) and the expiration codon ( UAG, UAA or UGA ) .
On the 5’side that is on the induction codon site, there is the leader part and on the 3 ‘ side, which is on the expiration codon side, there is the tail part. There are besides intercistronic C part of variable length.
At 5’cap 7 methylalanylate is connected to the terminal nucleate of the RNA by 5′-5 ‘
triphosphate linkage which protects the messenger RNA from enzymatic debasement. At the 3 ‘ terminal of messenger RNA, poly ( A ) tail is present.
The eucaryotic messenger RNA retains 5 ‘ and 3 ‘ untranslated parts ( UTRs ) . 5 ‘ UTR can be 100s of bases in length and 3’UTR can be kilo base in length. In procaryotes, 5 ‘ and 3 ‘ UTRs are shorter than that of eucaryotes.
( Beginning: Weil, 1996 )
Figures: Structure of messenger RNA.
( Beginning: messenger RNA construction, n.d )
The familial information is transcribed from DNA into messenger RNA in the signifier of three codification. Each amino acid is encoded by one or more than three codons in messenger RNA. There are start codons and stop codons. Translation starts from the start codon which codes for methonine and the codon is AUG. Translation returns from 5 ‘ to 3 ‘ end point of messenger RNA and Michigans when making the halt codons ( UAA, UGA, UAG ) . The undisturbed sequence of codons in messenger RNA, called a reading frame is translated into sequence of aminic acids in a polypeptide concatenation.
( Beginning: Prince alberts et al, 2008 ) .
R RNA ( construction and map )
In procaryotes, there are three types of rRNAs. These are 5S, 16S and 23S where as in eucaryotes, there are four types of R RNAs and these are 5S, 5.8S, 18S and 28S. It represents about 70- 80 % of entire cellular RNA. rRNA is a individual stranded polypeptide concatenation which forms a coiling construction. It is extremely folded, compact and 3dimensional construction that forms the major constituent of a ribosome.
rRNA forms the primary construction of a ribosome.
It forms catalytic part of the ribosome for peptide bond formation in transfer RNA with aminic acids. It binds tRNA and other accoutrement proteins for protein synthesis.
Figure: Structure of rRNA.
( Beginning: construction of rRNA, n.d )
Figure: The Mechanism of Protein Synthesis ( Central Dogma ) .
( Beginning: Protein synthesis mechanism, n.d )