Category: Biology Second Paper

The RNA that acts as the main structural component of ribosomes is called ribosomal RNA or rRNA. They are extremely permanent and insoluble. 80-90% of cells are rRNA. That is, it is the main part of the ribosome. Its molecular weight is 5-20 lakh daltons. Each rRNA molecule is made up of about 3,000 nucleotides. It is unbranched and unbranched. However, if the ionic level increases, a two-factor condition may occur in some places. Adenine and uracil and guanine and cytosine pair at the double-stranded position. rRNA combines with proteins to form ribonucleoprotein particles. There are three types of rRNA in progenitor cells (23S, 16S, 5S) and four types (28S, 18S, 5.8S, 5S) in protocells.
Function: rRNA forms ribosomes and helps in protein synthesis.

RNAs that carry genetic signals from the DNA of cells are called mRNAs or messenger RNAs. This is called template RNA or monocistronic mRNA. It is a beginning and very temporary. Their molecular weight is 5-20 lakh daltons. About 5-10% of the cell is mRNA.

Structure of mRNA
(i) Guanine cap: Guanine is added to the 5 end of mRNA to form a cap. This is called a guanine cap. The guanine cap consists of 7 guanosine nucleotides. This cap ensures ribosome attachment during translation.
(ii) Non-coding region-1: The region which does not synthesize protein is called non-coding region. This region consists of 10-100 nucleotides after the cap. It is rich in adenine and uracil. Translation does not occur here.
(iii) Initiation codon: The codon which initiates protein synthesis is called initiation codon. The start codon is AUG. It binds to the amino acid methionine.
(iv) Coding region: The region that synthesizes the protein is called coding region. This region consists of 1500 nucleotides. Translation occurs in this region.
(v) Termination codon: The codon which terminates protein synthesis is called termination codon. The termination codons are UAA, UAG and UGA. If any one of these codons is present, protein synthesis stops.
(vi) Non-coding region-2 : This region consists of 50-150 nucleotides. No translation here.
(vii) Poly A tail: Adenine is added to the 3 end of mRNA to form poly A tail. It is composed of 200-250 adenines.
Function: mRNA carries the protein-making signal from the nucleus to the cytoplasm and forms the chain of amino acids.

(i) Guanine cap: Guanine is added to the 5 end of mRNA to form a cap. This is called a guanine cap. The guanine cap consists of 7 guanosine nucleotides. This cap ensures ribosome attachment during translation.
(ii) Non-coding region-1: The region which does not synthesize protein is called non-coding region. This region consists of 10-100 nucleotides after the cap. It is rich in adenine and uracil. Translation does not occur here.
(iii) Initiation codon: The codon which initiates protein synthesis is called initiation codon. The start codon is AUG. It binds to the amino acid methionine.
(iv) Coding region: The region that synthesizes the protein is called coding region. This region consists of 1500 nucleotides. Translation occurs in this region.
(v) Termination codon: The codon which terminates protein synthesis is called termination codon. The termination codons are UAA, UAG and UGA. If any one of these codons is present, protein synthesis stops.
(vi) Non-coding region-2 : This region consists of 50-150 nucleotides. No translation here.
(vii) Poly A tail: Adenine is added to the 3 end of mRNA to form poly A tail. It is composed of 200-250 adenines.
Function: mRNA carries the protein-making signal from the nucleus to the cytoplasm and forms the chain of amino acids.

RNA that carries amino acids to the ribosome where proteins are made is called tRNA or transfer RNA. It is the smallest RNA and has a molecular weight of 25,000 daltons. About 15% of the cell is tRNA. Each tRNA molecule is made up of 90 nucleotides. It is produced in the nucleolus of the cell. tRNA molecules contain some unusual bases. Such as inosinic acid, thiamine etc. They are highly stable and make proteins for cells. There are about 100 types of tRNA in living organisms. A cell contains 31-42 types of tRNA.
According to scientist R. Holley’s clover leaf model in 1965, tRNA molecule consists of 5 arms.
(i) Subscriber arm: 3 and 5 ends of tRNA lie side by side to form the subscriber arm. It contains 7 base pairs. In addition, there are 4 additional unpaired nucleotides at the R3 end. 3 ends contain the -CCA sequence and the fourth A or G. The CCA sequence is called the amino acid attachment site. Amino acids are attached at this point. 5 ends with G or C.
(ii) D arm: The second arm of tRNA is D arm. It consists of 15-18 nucleotides. The D arm consists of 3-4 base pairs and its loop consists of 7 unpaired nucleotides. D arm loop is called loop-1 or Dihydrouridine or D loop.
(iii) Anticodon arm: The third arm of tRNA is called anticodon arm. The anticodon arm consists of 5 base pairs and its loop consists of 7 unpaired nucleotides. Its leak is called leak-2. The 3 nucleotides between the loops form the anticodon. It acts as a complementary codon to mRNA during protein synthesis.
(iv) Variable arm: Variable arm is of two types. Stemless and stemmed arms. Stemless arms have 4-5 bases and a loop. Stem arms consist of 13-21 bases and a loop.
(v) T arm: T arm has both stem and loop. Its stem is made up of 5 base pairs and the loop is made up of 7 nucleotides. The T arm contains a ribosome site. Its loop contains ribothymine, pseudouracil and cytosine bases.
tRNA carries amino acids to mRNA during protein synthesis.

According to scientist R. Holley’s clover leaf model in 1965, tRNA molecule consists of 5 arms.
(i) Subscriber arm: 3 and 5 ends of tRNA lie side by side to form the subscriber arm. It contains 7 base pairs. In addition, there are 4 additional unpaired nucleotides at the R3 end. 3 ends contain the -CCA sequence and the fourth A or G. The CCA sequence is called the amino acid attachment site. Amino acids are attached at this point. 5 ends with G or C.
(ii) D arm: The second arm of tRNA is D arm. It consists of 15-18 nucleotides. The D arm consists of 3-4 base pairs and its loop consists of 7 unpaired nucleotides. D arm loop is called loop-1 or Dihydrouridine or D loop.
(iii) Anticodon arm: The third arm of tRNA is called anticodon arm. The anticodon arm consists of 5 base pairs and its loop consists of 7 unpaired nucleotides. Its leak is called leak-2. The 3 nucleotides between the loops form the anticodon. It acts as a complementary codon to mRNA during protein synthesis.
(iv) Variable arm: Variable arm is of two types. Stemless and stemmed arms. Stemless arms have 4-5 bases and a loop. Stem arms consist of 13-21 bases and a loop.
(v) T arm: T arm has both stem and loop. Its stem is made up of 5 base pairs and the loop is made up of 7 nucleotides. The T arm contains a ribosome site. Its loop contains ribothymine, pseudouracil and cytosine bases.
tRNA carries amino acids to mRNA during protein synthesis.

RNA that carries amino acids to the ribosome where proteins are made is called tRNA or transfer RNA. It is the smallest RNA and has a molecular weight of 25,000 daltons. About 15% of the cell is tRNA. Each tRNA molecule is made up of 90 nucleotides. It is produced in the nucleolus of the cell. tRNA molecules contain some unusual bases. Such as inosinic acid, thiamine etc. They are highly stable and make proteins for cells. There are about 100 types of tRNA in living organisms. A cell contains 31-42 types of tRNA.

RNAs that act as carriers of heredity are called genetic RNAs. Some viruses contain RNA instead of DNA. All these RNAs carry hereditary characteristics. Genetic RNA can cause enzyme synthesis and protein coating. Viruses like Dengue, Polio, Mumps, TMV, HIV, Rabies, Reo virus, Dwarf virus, Retro virus etc. contain genetic RNA.

RNA molecules are made up of three chemical components. These are-
1. Nitrogen Alkali: This alkali is formed by carbon, hydrogen, oxygen and nitrogen. Alkaline compounds form rings. Based on the number of rings, nitrogenous bases can be divided into two groups.
(i) Purines: Dicyclic nitrogenous bases are called purines. Its common symbol is C5H4N4. It is composed of adenine and guanine.
(ii) Pyrimidine: A cyclic nitrogenous base is called pyrimidine. Its common symbol is C4H4N2. It is composed of cytosine and uracil.
2. Pentose sugars: Five carbon sugars are called pentose sugars. RNA molecules contain the ribose sugar. It is a type of monosaccharide. Ribose sugar is so named because it has a hydroxyl group at the 2nd carbon.
3. Phosphoric acid: One of the chemical components of RNA molecules is phosphoric acid. Its molecular symbol is H3PO4. It contains one divalent oxygen atom and three monovalent hydroxyl groups. Oxygen and hydroxyl groups combine with a pentavalent phosphorus atom to form phosphoric acid.
A molecule of pentose sugar and a molecule of nitrogen base combine to form a molecule of nucleoside. Again, one molecule of phosphate joins with one molecule of nucleoside to form one molecule of nucleotide. The smallest RNA molecule can contain 22 and the largest RNA molecule can contain 10,000 nucleotides.

All cells contain RNA. It is located in the cell cytoplasm, nucleus, ribosomes, chromosomes, mitochondria, chloroplasts etc. 90% of the RNA of the cell is in the cytoplasm and 10% of the RNA is in the nucleus. Some bacteria E. coli, Xanthomonas, Cyanobacteria, Francisella etc. contain RNA. Most plant viruses contain RNA. RNA viruses such as TMV, HIV, dengue, polio, mumps, measles, measles, rabies, influenza, arbovirus, coronavirus, reovirus, rice dwarf virus, retrovirus etc.

Ribonucleic acid is abbreviated as RNA. The monomer units of nucleotides of nucleic acid are made up of ribose sugar, adenine, guanine, cytosine, uracil and phosphoric acid is called RNA. In 1963 P.J. Gomatos & I. Tamm discovered the existence of double-stranded RNA molecules in Reovirus. Rice dwarf virus contains double-stranded RNA.