The DNA code contains instructions needed to make the proteins and molecules essential for our growth development and health.
Proteins are molecules made of amino acids that are necessary for every activity in the body. They are present in every cell and tissue, each one with a highly specialized function coded by our genes.
There are 20 different types of amino acids that can be combined to make a protein. The sequence of amino acids determines each protein’s unique three-dimensional structure and its specific function. That is, each protein must fold up into a particular shape in order to perform its function in the cell.
Proteins have different shapes and molecular weights, depending on the amino acid sequence. For example, haemoglobin is a globular protein that folds into a compact globe structure, but collagen found in our skin is a fibrous protein that folds into a long extended fibre chain.
Because form determines function, any slight change to a protein’s shape may cause the protein to become dysfunctional.
Every cell contains thousands of different proteins which work together as tiny machines to run the cell. Cells use the information encoded in their genes, which are like a protein library, as the “blueprint” for making proteins. Each gene in DNA encodes information about how to make an individual protein.
From DNA to protein:
The flow of genetic information within a biological system is explained in the “Central Dogma” of molecular biology. It was first stated in 1957 by Francis Crick, the discoverer of the DNA structure and thereafter published in Nature magazine in 1970.
The central dogma of molecular biology deals with the detailed residue- by- residue transfer of sequential information. It states that such information cannot be transferred back from protein to either protein or nucleic acid.
Francis Crick (Nature, vol. 227, 1970)
The central dogma suggests that DNA contains the information needed to make all our proteins and that RNA is the messenger that carries this information to the ribosomes. It explains that DNA codes for RNA which codes for proteins.
Protein synthesis is a complex, multi-stage process and many things can go wrong along the way. A protein that has not been synthesized correctly may be non-functional or toxic.
What happens when protein synthesis does not work properly?
Protein synthesis is basically transcribing RNA to make a protein. Errors or mutations are a disruption in the conversion of a coding sequence into a functional protein.
Indeed, if the mRNA makes a mistake and copies one of the codons incorrectly, the amino acid that is put onto the protein molecule will be incorrect and this changes the structure and function of the entire protein.
Copying errors can insert or delete extra letters of the genetic code and have a significant impact because they change the organism’s phenotype.
For instance, Microdeletion syndromes are a group of clinically recognisable disorders characterised by a small deletion of a chromosomal segment spanning multiple disease genes, each potentially contributing to the phenotype independently. They are identified by their genomic positions and their size.
Most microdeletions have no clinical consequences, but some are characterized by a complex clinical and behavioural phenotype.
The most common are DiGeorge, Cri Du Chat and Prader-Willy syndromes.
Due to technological advancements in predictive and precision medicine, nowadays DNA screening tests offer families and doctors the earliest and most complete information on eventual chromosomal disorders in the fetus.
The analysis of cell free fetal DNA in the mother’s bloodstream detects trisomies 21, 18 and 13, sexual aneuploidies and microdeletions with an accuracy up to 99.9%.
To learn more about risk- free fetal DNA test for early detection of chromosomal disorders, including Down syndrome, see Tranquility the non invasive prenatal trisomy test by Genoma, performed on a standard maternal blood draw.