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How does information from a gene make a protein?

A gene is defined as a section of DNA that codes for a protein. Within a gene you have triplets which are 3 bases in a row that code for a specific amino acid. However there might be many triplet codes per amino acid. Amino acids are the building blocks of proteins so the cell transfers the information in the gene into a protein in two major steps: Transcription and Translation. Below the steps are explained as if in a eukaryotic cell.

 

1. Transcription - DNA to mRNA

Initially helicase unzips the DNA helix by breaking the double bonds. This exposes the bases of the sense strand of DNA, which is used to make a complementary mRNA strand. RNA polymerase joins the RNA nucleotides to form a single strand of mRNA which leaves the nucleus through a pore in the nuclear envelope. The triplet codes in the DNA are now called codons within the mRNA strand. The base T (thymine) has also been exchanged for (uracil). 

 

2. Translation - mRNA to protein 

This step occurs within ribosomes which are located either free in the cell or on the rough endoplasmic reticulum. The amino acids are carried by tRNA which has 3 bases which code for a specific anti-codon to the amino acid being carried. This anti-codon will be complentary to a specific codon in mRNA which is the mRNA form of the triplet coded in the DNA at the beginning. 

The mRNA from the nucleus moves into the ribosome and the first codon is called a start codon which initiates translation. tRNA molecules then bind to each specific codon in order and the amino acids carried are bonded together via a peptide bond. The empty tRNA molecule then leaves the ribosome. This process continues until the ribosome reaches the end of the mRNA strand and stops at the stop codon which does not code for an amino acid. The polypeptide chain is then released and it folds into its secondary structure. The protein is most likely to then move to the golgi apparatus where it is edited and modified into its final structure. 

 

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