Monday, August 30, 2010

RNA, its Structure and Kinds

RNA is Ribo nucleic acid. It occurs in the nucleolic, chromosomes and cytoplasm. About 90% of cells RNA occurs in the cytoplasm. RNA consists of 5 – carbon ribose sugar and phosphate. RNA is macro molecule and is single stranded.
RNA is chemical messenger and plays key role in the process of protein synthesis.
RNA is the other nucleic acid. It is high molecular weight polynucleotide. It differs from DNA in having Pentose sugar ribose in place of deoxyribose and in that pyrimidine thymine is here replaced by uracil. Other three bases are the same as in DNA. The nucleotides (combination of ribose and base molecules) of RNA are called ribo-sides and its nucleotides are called ribotides. RNA is therefore described as polycribotide. Various ribotides are joined together by their phosphate groups to form an un-branched linear chain containing hundreds of ribotide (nucleotide) units. RNA molecule is single strand structure and not double strand structure. Its molecule is smaller and has lower molecular weight than DNA. There are three kinds of RNA which play important roles in the translation of genetic information contained in DNA. RNA is formed in the Nucleus by nuclear DNA. A part of it is present in the chromatin and nuclear ribosomes in the form of ribo-nucleoprotein. Most of it however is located in the cytoplasm, particularly in the cytoplasmic ribosomes. RNA formed in the nucleus is stored in the nucleolus from where it passé out through nuclear membrane into the cytoplasm.

Structure of RNA:

Kinds of RNA:
A cell contains many kinds of RNA. There are three major kinds:

(1)        Ribosomal RNA:
RNA found in ribosomes is called ribosomal RNA or rRNA. During polypeptide synthesis, rRNA molecules provide the site on ribosome where polypeptide bond is assembled.













(2)        Transfer RNA:
Second type of RNA is called Transfer RNA or tRNA which is much smaller. Human cells contain more than 40 different kinds of tRNA molecules which float free in the cytoplasm. During polypeptide synthesis tRNA molecules transport the amino acids present at their one end to the ribosome for use in building the polypeptide and position each amino acid at the correct place on elongating polypeptide chain.






(3)        Messenger RNA:
Third of RNA is messenger RNA. Each mRNA molecule is long, single strand of RNA that passes from the nucleus to the cytoplasm. During polypeptide synthesis mRNA molecules bring information from the chaeomosomes to ribosomes to direct the assembly of amino acids into a polypeptide.
These molecules together with ribosomal proteins and certain enzymes constitute a system that carries out the task of reading the genetic message and producing the polypeptide that the particular message specifies.

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