Nucleic acids are the chemical compounds that make up out genetic data. It comprises of a 5 carbon ribose sugar backbone, a phosphate group and a nitrogenous base.
Nucleic acids can fall under two categories
- Ribonucleic acids (RNA)
- Deoxyrubonucleic acids (DNA)
Deoxyribonucleic acid as the name suggests is in lack of an -OH group, well the O to be specific.
Ofcouse one must remember that DNA and RNA are large macromolecular structures, the individual monomer which make them up an consist of the 5 carbon sugar, nitrogenous base and the phosphate group is singularly called a nucleotide.
The nitrogenous bases:
There are 5 nitrogenous bases which make up nucleic acids:
- Adenine
- Cytosine
- Guanine
- Thymine
- Uracil
Differences between DNA and RNA:
DNA:
- Stores genetic information
- Exists in a helical structure
- Has a long chain of nucleotides
- Adenine-Thymine & Cytosine-Guanine base pairs
- Is self replicating
- Is generally stable because of existence of more C-H bonds
RNA:
- Transfers genetic information for the synthesis of proteins for which it codes for (production is via ribosomes mRNA & tRNA)
- Exists as a single strand
- A shorter chain of nucleotides
- Adenine-Uracil & Cytosine-Guanine base pairs
- Only synthesized then the production of DNA is needed
- Is generally more reactive die to the presence of more C-OH bonds
The helical structure of DNA is cause by the bonding in between the base pairs along the anti parallel strands of the DNA strands. Bases Adenine and Guanine are referred to as purines whereas Cytosine and Thymine are referred to as pyrimidines. These base pairs are held together via hydrogen bonds
As you can see, the order in which bases are hydrogen bonded to each other is Pyrimidine to Purine and vice versa. Why doesn’t Thymine bond with Guanine or Cytosine to Adenine? This is because for this bond to be stable and efficient each of the individual bases must have the same number of substituents which are able to undergo a complete hydrogen bond. The manner by which bonds are always C-G & A-T is referred to as Chargaff’s Rules.
“There is not enough space for two purines to fit within the helix and too much space for two pyrimidines to get close enough together for hydrogen bonds to form between them”
References:
http://www.etap.org/demo/biology_files/lesson5/instruction2tutor.html
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