Structure of DNA
A strand of DNA is made up of a double helix. When it is unwound it consists of phosphate, sugar and one of four organic base/nitrogen molecules called nucleotides. The sugar and the phosphate form the two strands along the sides of the helix and the bases are joined by hydrogen bonds that form ties like rungs on a ladder.
The role of DNA in Cell Division
DNA is found in the cell nucleus, which has a Nuclear Envelope Pore. The role of DNA is to provide instructions for proteins to be produced in the cytoplasm. However, DNA can’t pass through the Nuclear Envelope Pore of the nucleus to the cytoplasm.
Therefore the DNA has to pass accurate instructions from the nucleus to the cytoplasm. This is done by DNA replication where the DNA helix unfolds and free nucleotides (RNA) align alongside the DNA with the same organic base (A, C, T & G), and joins together to form the mRNA. This part of the process is called transcription. (Note, a U base replaces a ‘T’ base on the mRNA).
Unlike DNA the mRNA containing the same genetic information as the DNA can pass through the Nuclear Envelope Pores into the cytoplasm where proteins are produced. This information is going to be used in the production of new proteins. Therefore, its structure and DNA replication process is suited to the process of cell division.
The role of DNA in Protein Synthesis
Once the mRNA is in the cytoplasm the production of new proteins can begin, this process is called Protein Synthesis.
The mRNA that is carrying exactly the same genetic information as the DNA attaches itself to a ribosome that it freely floating in the cytoplasm.
The bases on the mRNA are coded in sets of three each set of three is called a codon. These sets of bases are read and a transfer RNA (tRNA) with anticodons (opposite bases to mRNA) attaches itself to the mRNA. In turn a freely floating amino acid is attracted and attached to the tRNA on the first three bases. The same process continues on the next three bases and a peptide bond is formed between the two amino acids that are side by side. Once the bond is formed the tRNA on the first three bases is released back into the cytoplasm.
The ribosome then moves along the mRNA to the next three bases where the process is repeated until a complete chain of amino acids (polypeptide chain) form a protein molecule. These amino acid chains will form a specific protein that is needed to produce new cells in the body.
The process of reading the mRNA and turning the codes into new codes is called translation. Without the structure and replication of the DNA this process would not be possible.
