Nucleic acids are a group of molecules that include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)
- A nucleotide is made up of 3 components:
- Pentose Sugar
- Phosphate group
- A nitrogen containing organic base (Adenine, cytosine, thymine, guanine and uracil)
- All 3 components are joined through a condensation reactions to form 1 nucleotide.
- Two mononucleotides can join together as a result of a condensation reaction between one of the phosphate groups on one mononucleotides to the deoxyribose sugar on the other mononucleotides. The bond formed is a phosphodiester bond. The resulting product is a dinucleotide where if more nucleotides are added it then results in a polynucleotide
Ribonucleic Acid (RNA) Structure
- Ribonucleic acid is a polymer made up of nucleotides
- It is relatively short chain (especially when compared to DNA)
- RNA is a polynucleotide chain where the pentose sugar is always ribose and the organic bases are Adenine, Guanine, Cytosine and Uracil.
- One example of RNA transfers genetic information from the DNA to the ribosomes which has its own RNA strand to create proteins and other types of RNA. Other RNA can be found in the production of protein synthesis
Deoxyribonucleic Acid (DNA) Structure
- Deoxyribonucleic acid is a polymer made up of nucleotides
- It is long chain (especially when compared to RNA)
- DNA is a polynucleotide chain where the pentose sugar is always ribose and the organic bases are Adenine, Guanine, Cytosine and Thymine.
- DNA is made of 2 strands, with hydrogen bonds joining them together
- The phosphate groups and the deoxyribose molecule alternate u[p the polynucleotide chain
- The bases on the two strand are joined together through hydrogen bond which holds the entire DNA molecule together
- The base pairs are specific to each other:
- Adenine and Thymine (uracil in bacteria)
- Guanine and Cytosine
Guanine will always and only bond to cytosine, therefore guanine’s complimentary base pair is cytosine. and adenine complimentary base pair is thymine (or uracil)
- The amount of adenine and thymine, and guanine and cytosine are always the same however it is the ratio of the adenine and thymine to guanine and cytosine which varies from between different species
The stability of DNA
- The phosphodiester backbone protects the more chemically reactive organic bases inside the double helix
- The hydrogen bonds between the organic base pairs form bridges (rungs) between the phosphodiester uprights.
- Between the cytosine and guanine are 3 hydrogen bonds, therefore increasing the stability of the molecule as a whole compared to the adenine and thymine which has 2 hydrogen bonds.
- As the molecule is so stable, it is rare for mutations to occur which makes it ideal for carrying hereditary material that is passed on generation after generation
Function of DNA
- DNA is a hereditary material responsible for passing genetic information from cell to cell and generation to generation
- There are in total 3.2 billion base pairs in DNA for a typical mammalian cell
- During DNA replication, the weak hydrogen bonds between the base pairs are able to separate to reveal their code
- By having the actual genetic code embedded into the phosphate backbone, it protects the material from being corrupted by outside chemicals or physical forces
- Base pairing allows for DNA to replicate and transfer information as mRNA
- The carbon atom in the pentose sugar are numbered of particular importance as 3’ (3 prime) and 5’ (5 prime) carbon atoms.
- 5’ has an attached phosphate group
- 3’ has a hydroxyl group
- When nucleotides are organised in to the double helix stand, one of the strands run in the 5’ to 3’ direction whilst the opposite strand runs in a 3’ to 5’ direction
- The two strands are said to be antiparallel