Biomolecules & Polymers Nucleic Acid

NUCLEIC ACID (a) These are special type of acids which are present in nucleus & cytoplasm. (b) Control the metabolic activities of cell. (c) They are also found in Mitochondria, centriole and chloroplast. Types  These are of 2 types DNA (Deoxyribonucleic acid) RNA (Ribonucleic acid) (d) Fischer discovered Nitrogen bases in 1888 (e) Levan found sugar Nitrogen Base type Purine Pyrimidine 2 type Ribose (RNA) Decoxyribose (DNA) DEOXYRIBONUCLEIC ACID (D.N.A.) : STRUCTURE OF DNA (DEOXYRIBONUCLEIC ACID) : J.D. Watson and F.H.C. Crick (1953) proposed double helical structure of DNA based on the results of M.H.F. Wilkins and co-workers. All these three persons were awarded Nobel Prize in 1962 for this work. The following are some of the characteristic features of double helical structure of DNA. (i) Each nucleotide consists of sugar, phosphate and a nitrogenous base. Many such nucleotides are linked by phosphodiester bonds to form a polynucleotide chain or strand. (ii) Phospho diester bonds are formed between 5’carbon of sugar of one nucleotide and 3' carbon of sugar of the next nucleotide. (iii) Nitrogenous base is attached to1’ carbon of sugar. At this place purine base is attached by its 5' position and pyrimidine by its 3' position. (iv) Polynucleotide strand is made of backbone of sugar and phosphate forming its long axis and bases at right angles to it. BIOMOLECULES & POLYMERS (a) It is found in Nucleus. (b) They on pneumococcus bacteria. (c) DNA made up of 3 units- Nitrogen base Deoxyribose Sugar Pyrimidine Phosphric acid (H3PO4) Purine (i) Thymine (i) Adenine (ii) Cytosine (ii) Guanine (d) Nucleoside When nitrogen base combined with deoxyribose sugar it constitute a nucleoside. S.No. Deoxyribonucleoside 1 Adenine + Deoxyribose  Deoxyadenosine 2 Guanine + Deoxyribose  Deoxyguanosine 3 Cytosine + Deoxyribose  Deoxycytidine 4 Thymine + Deoxyribose  Deoxythymidine Nucleotide (a) Nitrogen base+Sugar+Phosphate  Nucleotide (b) Nucleotide is a unit of DNA. (c) All nucleotides combined and form a chain called polynucleotides by which RNA and DNA formed. FUNCTION OF DNA (i) Self - Replication or self -Duplication DNA has the property of self - replication . It is therefore a reproducing molecule. This unique property of DNA is at the root of all reproduction. Through its replication, DNA is acts as the key to heredity. In the replication of DNA, the two strands of a double helix unwind and separate as a template for the formation of a new complementary strand. (ii) Protein Synthesis The specific sequence of base pair in DNA represents coded information for the manufacture of specific proteins. These code instructions first are transcribed into the matching nitrogen- base sequences within mRNA and the instructions in such RNA subsequently are translated into particular sequence of amino acid units within the polypeptide chains and proteins. The major steps in the utilization of the genetic information can be represented as : D NA Replication D N A Transcription RIBONUCLEIC ACID (RNA) :  Found in cytoplasm as well as in nucleus. Cytoplasm  In the ribosome (higher amount) RNA Transcription Protein BIOMOLECULES & POLYMERS CHEMICALNATURE  Ribonucleic acid is a polymer of purine and pyrimidine ribonucleotides linked by 3'  5' phosphodiester bridges. The number of nucleotides in RNA ranges from as few as 75 to many thousands. Although sharing many features with DNA, RNA possesses several specific difference.  As indicated by its name, sugar in RNA to which the phosphate and nitrogen- bases are attached is ribose rather than the deoxyribose of DNA.  Although RNA contains the ribonucleotides of adenine, guanine, and cytosine, it does not posses thymine. Instead of thymine, RNA contains the ribonucleotides of uracil. Thus the pyrimidine components of RNA differs from those of DNA.  RNA exists basically as a single-stranded molecule rather than as a double -stranded helical molecule, as does DNA. However the single strand of RNA is capable of folding back on itself like a hairpin and thus acquiring double-stranded characteristics. In these regions. A pairs with U and G pairs with C. Thus a given segment of a long RNA molecule might, for example, be represented as follows. P–R–P–R–P–R–P–R–P–R | | | | | A U G G C  where R stands for ribose ; A, U, G, and C for Adenine, Uracil, Guanine and Cytosine respectively. TYPES OF RNA AND THEIR FUNCTIONS : There are 3 main types of RNA molecules (i) Messenger RNA (mRNA) (ii) Transfer RNA (tRNA) (iii) Ribosomal RNA (rRNA) (i) Messenger RNA (mRNA)  This type of RNA consists of single strand of variable length and serves as a template for protein synthesis. Codon in the chromosomes.  mRNA forms complementary copy of DNA as it carries chemical messages in the form of nitrogen-base sequence from the nucleus to the ribosomes, i.e. from DNA to cytoplasm where proteins are synthesized. Therefore, it is called messenger RNA or mRNA  mRNA is synthesised from DNA in the nucleus.  It is called transcription. (ii) Ribosomal RNA  A ribosome is a cytoplasmic nucleoprotein structure which serves as the organellar machinery for protein synthesis from mRNA templates.  On the ribosome, the mRNA and tRNA molecules interact to translate into a specific protein molecule the information transcribed from the DNA.  rRNA constitutes the largest part of total RNA (Highest) - 80% (iii) Transfer RNA (RNA) :  These are also called Soluble RNA.  Single stranded.  10-15% of the total RNA.  Size - Smallest  75 - 80 nucleotides only.  Synthesis - Within nucleus from DNA. Function- It transport amino acid from cyto plasm to the site of protein synthesis. Differences Between DNA and RNA DNA RNA 1. It usually occurs inside nucleus and some cell organelles . 1. Very little RNA occurs inside nucleus. most of it is found in the cytoplasm. 2. DNA is the genetic material. 2. RNA is not the genetic material except in certain viruses, e.g. Reovirus. 3. It is double stranded with the exception of itsome viruses (e.g. × 174). 3. RNA is single stranded except reovirus where is double stranded. 4. DNA contains over a million nucleotides. 4. Depending upon the type, RNA contains 70-1200 nucleotides. 5. DNA is of only two types; intra-nuclear and extra-nuclear. 5. There are at least three types of RNAs— mRNA, rRNA and tRNA 6. It contains deoxyribose sugar. 6. It contains ribose sugar. 7. Nitrogen base thymine occurs in DNA alongwith three others — adenine, cytosine and guanine. 7. Thymine is replaced by uracil in RNA The other three are similar — adenine, cytosine and guanine. 8. It replicates to form new DNA molecules. 8. It cannot normally replicate itself. 9. DNA transcribes genetic infromation to RNA. 9. RNA translates the transcribed message for forming polypeptides. 10. DNA controls metabolism and genetics Including variations. 10. It only controls metabolism under instruction from DNA. 11. Purine and pyrimidine bases are in equal number. 11. There is no poroportionality between number of purines and pyrmidine bases.