Effect of genetic variants on phenotype – Higher
The structure of DNA is important for synthesising specific proteins that are needed in biological processes.
Mutations in coding DNA
If you get a mutation in coding DNA, then the sequence of DNA could be changed. Changing the sequence of DNA can change the amino acids that make up the protein. This could have huge consequences. Enzymes are made of proteins. They have a specifically shaped active site that recognises a certain substrate. If a random mutation happens in the coding DNA that codes for the enzyme, then the wrong amino acids could be used to make the enzyme. This could change the shape of the enzyme's active site and then the enzyme will not work properly.
Mutations in non-coding DNA
Not all parts of DNA code for proteins. As well as the coding parts of DNA that code for proteins, there are also non-coding parts of DNA. The non-coding parts of DNA can switch genes on and off. When genes are switched off, the process of Making an mRNA copy of the DNA in a gene. stops. This means no mRNA is the substance that carries a complementary copy of a gene from the DNA in the nucleus to the ribosomes in the cytoplasm. is being made for that gene and therefore no protein can be made for that gene. Therefore, a mutation in non-coding areas of DNA may affect When genes are instructed to make gene products, mostly proteins. Controlling gene expression means controlling which proteins are made by the cell., and whether the correct protein is synthesised or not.
The diagram below shows DNA with certain genes switched on and some switched off:
Red boxes – genes switched on
White boxes – genes switched off
This diagram shows the DNA when all of the genes are switched off:
In different cells around the body, genes will be switched on and others will be switched off. This will vary depending on which cells are examined.
