Ribonucleic acid (RNA) structures and function

RNA

• Ribonucleic acid (RNA) is a biopolymer macromolecule as DNA. It consists of small subunits called nucleotides composed of:

− Purine nucleobases [Adenine−(A), Guanine−(G)]

− Pyrimidine nucleobases [Cytosine−(C), Uracil−(U)]

− Ribose pentose sugars [C₅H₁₀O₅]

− Phosphate groups [PO₄^3-]






• The nucleobase is attached on the ribose by an glycosidic bond.
• The ribose is bonded to the phosphate group through ester bonds.

• Differences between DNA and RNA

• DNA	RNA
  A,G,C or T base	A,G,C or U base
  Double stranded	Single stranded
  2'−deoxy−D−ribose pentose sugar	D−ribose pentose sugar
  Adenine=Thymine and Guanine=Cytosine	Adenine=Uracil and Guanine =Cytosine

  
  
  
  
  
  
• RNA have 3 types which is mRNA,tRNA and rRNA.
• Messenger RNA (mRNA)-type of RNA that encodes proteins and is translated by the ribosome into proteins. Eukaryotic mRNA usually has a few different regions that look something like this:

Typical human protein coding mRNA

 Eukaryotic mRNAs undergo extensive processing directly after they are transcribed by an RNA polymerase. A cap is added on the 5′ end of the molecule which serves various functions including nuclear export, preventing exonuclease degradation, and aiding in translation initiation. A poly-A tail is also added to the 3′ end that also helps prevent mRNA degradation, among other things. Not to mention all the splicing to create the actual final mRNA.

• Transfer RNA (tRNA)-an essential component of translation, where their main function is the transfer of amino acids during protein synthesis. Therefore they are called transfer RNAs.  tRNA is the smallest of the 3 types of RNA having about 75-95 nucleotides.Each of the 20 amino acids has a specific tRNA that binds with it and transfers it to the growing polypeptide chain. tRNAs also act as adapters in the translation of the genetic sequence of mRNA into proteins. Therefore they are also called adapter molecules.Other than that,tRNAs have a clover leaf structure which is stabilized by strong hydrogen bonds between the nucleotides

• Ribosomal RNA (rRNA)-found in the ribosomes and account for 80% of the total RNA present in the cell.Though ribosomes are often described as proteins when we first learn about them, they are actually a combination of RNA and a bunch of proteins all working together.Different rRNAs present in the ribosomes include small rRNAs and large rRNAs, which denote their presence in the small and large subunits of the ribosome.

rRNAs combine with proteins in the cytoplasm to form ribosomes, which act as the site of protein synthesis and has the enzymes needed for the process. These complex structures travel along the mRNA molecule during translation and facilitate the assembly of amino acids to form a polypeptide chain. They bind to tRNAs and other molecules that are crucial for protein synthesis.