Nucleic acid

NUCLEIC ACID BY VIVEK KUMAR

1. Nucleic acid

2. intoduction Frederic miescher in 1869, isolated an acidic compound from the nuclear material of salmon sperm, and named it as nuclien which is now called nucleic acid. Any of the group of complex  compound  consisting of linear chains of  monomeric  nucleotides whereby each  monomeric  unit is composed of phosphoric acid, sugar and nitrogenous base, and involved in the preservation, replication and expression of herditory information in every living cell.

3. Structure of nucleic acid Nucleic acid are polynucleotide, means two or more nucleotide are joined with each other by a phosphodiaster bond. The phosphodiaster bond link the 3 ʹ carbon in the sugar ring of one nucleotide to the 5ˊ carbon on the next nucleotide. Nucleic acid is polymer of four nucleotides linked by alternating sugar- phosphate bonds.

4. Formation of nucleic acid Nucleosides (sugar + base) Nucleotides (sugar + base + phosphate) Nucleic acid ( DNA and RNA ) Phosphate group is attached Polymer of nucleotides

5. N ucleotide This is the monomer of nucleic acid or building block material for nucleic acid. A nucleotide has 3 main component: Sugar(2 type) Base (5 type) Phosphate (1-3)

6. DNA and RNA DNA is stands for deoxyribonucleic acid. DNA is mainly Ds(double stranded) but in some cases it is Ss(single stranded). DNA store genetic information presence mainly in nucleus and small amount in mitochondria and chloroplast. RNA stands for ribonucleic acid. RNA is mainly single stranded but in some cases it is double stranded.it is found in nucleus and mostly in cytoplasm. RNA is used in protein synthesis for putting genetic information presence almost throught the cell.

7. Chemical composition of DNA and RNA DNA- A macromolecules its building block is deoxyribose, nitrogen bases (A , G, C, T), and phosphate group (1-3). RNA- A macromolecules its building block is ribose, nitrogen bases(A, G, C, U) and phosphate group. In both DNA and RNA deoxyribose and ribose respectively joined to each other by phosphodiaster bond.

8. Types of DNA and RNA DNA-Depending upon ionic strength and humidity various form of DNA exist. The naturally occuring DNA is B- DNA. TYPE A-DNA B-DNA C-DNA Z-DNA Helix sense Right handed Right handed Right handed Left handed Diameter in A° 23 19 19 18 B.P /Turn 11 10.5 9.33 12

9. continue RNA-two type 1) genetic RNA. 2) non –genetic RNA. In cellular system RNA act as non genetic RNA. For example- r-RNA, m- RNA, t- RNA. Genetic RNA is found in some viruses for ex- Reterovirus , tumor virus, TMV( tobaco mosiac virus). 1) r-RNA- stands for ribosomal RNA, most abundant and most stable type of RNA. Act as structural constituent of ribosome.

10. continue 2)m RNA- stands for messenger RNA.less abundant and less stability as compared to the m-RNA. Two type: 1) Polycistronic m-RNA- Such m-RNA which has information for the synthesis of many polypeptide chain is called polycistronic m-RNA. It carries information of many cistron . In prokaryotes m-RNA is polycistronic . 2) Monocistronic m-RNA- such m-RNA which has information for the synthesis of single polypeptide chain.It carries information of single cistron . In eukaryotic m-RNA is monocistronic m-RNA.

11. continue Role-it carries information of synthesis of polypeptide chain in form of sequence of codon . 3)t-RNA-It stability and abundant are intermediate between that of r-RNA and m-RNA. Role-t-RNA is adaptor molicule which interpvent codon of m-RNA in term of amino acid.32 type of t-RNA is required to read 61 codon .

12. Chargaff's Rules Base composition of DNA of one spp differ from that of other spp. DNA isolated from different tissue of the same organism show identical base composition. Base composition of DNA does not depend upon organism age, nutritional level and environment. In every DNA- adenine residue is equal to the thymine residue and guanine residues is equal to the cytosine residues, mean some total of purine bases is equal to the pyramidine bases.

13. 4 th rule of Chargaff's determine complementry base pairing so that it failed in case of single stranded DNA.

14. continue Discovery of the DNA double helix A) Frederick Griffith – Discovers that a factor in diseased bacteria can transform harmless bacteria into deadly bacteria (1928). B) Rosalind Franklin - X-ray photo of DNA.(1952). C) chargaff given complementary base pairing in DNA. D)Then Watson and Crick - described the helix structure DNA molecule by using above given data in 1953 .

15. Double helix model of DNA Acc. To this model double helix structure of DNA are as follow: DNA has two polynucleotide strand which are coiled around the same axis to form right handed double helix. The backbone of each polynucleotide strand is hydrophilic and it is composed of alternate phosphate- sugar bond. The backbone of each strand is on outside, facing aqueous medium. Purine and pyramidine bases are stacked within the helix, facing non-aqueous medium. Bases of one strand show complementary base pairing with the base of other strand. Adenine pair with thymine with the help of 2-H bond and guanine pair with cytosine with the help of 3-H bond and vice-versa.

16. continue Spatial relationship of both strand produce major and minor groove in double helix. In stack of bases two bases are separated by a distance of 0.34nm(3.4A°). One turn of helix cover distance of 3.4nm(34A°).which include 10.5 base pair. Both strand of DNA are antiparallal. Stability of double helix depend upon base stacking interaction or hydrophobic iteraction due to H-bond formed between purine and pyramidine bases.

17. Different between DNA and RNA DNA RNA Structure/ shape Double helix Linear, single strand No. of strand mainly 2 strand but in some cases like in bacteriophase it is 1 strand Mainly 1 strand but in some cases like tobaco mosiac virus and reoviruses it is 2 strand. Sugar Deoxyribose Ribose Nitrogen bases A, T, G, C A, U, G, C Location Mainly in nucleus and few in mitochondria and chloroplast Nucleus and cytoplasm Function Store genetic information , contain protein codes and ensures each daughter cell and gametes receive exact genetic information. Perform non-genetic function but in some cases like in reteroviruses it act as genetic component. Replication It undergoes replication. Only genetic RNA undergo replication.