RIBONUCLEIC ACID (RNA)

 

Objectives of the discussion:  By the end of our discussion here, the reader/medical student will be able to;

1.  Explain the difference between DNA and RNA

2.  Clearly describe the sequential transfer of information from DNA to RNA to proteins

3.  Outline the different types of RNA

Introduction:  Ribonucleic acid (RNA) is also a polymer of purine and pyrimidine nucleotides linked by phosphodiester bonds.  RNA differs from DNA in a number of ways.  First, in here in RNA the nucleotide sugar base is Ribose while in DNA the sugar is  Deoxyribose.  Secondly, RNA is always a single stranded molecule and shorter than DNA, where as DNA is double stranded and extremely long molecule.  About 50% of cellular RNA is distributed in the ribosomes and endoplasmic reticulum; 25% in cytoplasm; 15% in mitochondria and the rest 10% in nucleus.  Cellular RNAs are of 5 types varieties. They are very stable. Small Nuclear RNAs (SnRNAs) are a subgroup of small RNA.  Some important species of SnRNAs are U1 (165 nucleotides), U2 (188 nucleotides), U3 (216), U4 (139), U5 (118), U6 (106).  They are involved in mRNA splicing that is to say Micro-RNA (miRNA). They alter the function of mRNA. They are moderately stable.

Central Dogma of Molecular Biology:  The information available in the DNA is passed to messenger RNA, which is then used for synthesis of a particular protein.  In this process, we find Replication, Transcription and Translation.  DNA replication is like printing a copy of all the pages of a book. The replication process occurs only at the time of cell division.  But transcription is taking place all the time. Only certain areas of the DNA are copied (selected regions on the sense strand). This is like taking a copy of particular page of the book.  So, the genetic information of DNA is transcribed (copied) to the messenger RNA (mRNA). During transcription, the message from the DNA is copied in the language of nucleotides (4 letter language).  The mRNA then reaches the cytoplasm where it is translated into functional proteins.  During translation, the nucleotide sequence is translated to the language of amino acid sequence (20 letter language).

RELATED;

1.  NUCLEOTIDES

2.  DNA THE GENETIC MATERIAL

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