We are our DNA!
Held in our cell nuclei, it’s a long chain of tightly wound-up coded instructions which cells unravel, read and use to make proteins or polypeptides.
When cells want to make a certain protein, they read DNA in chunks called genes that code for a specific sequence of amino acids.
Like proteins, DNA is also a polymer but of repeating nucleotides- a group made of a phosphate group on a sugar attached to a nitrogenous base.
Nucleotides link together to make the double helix structure of DNA.
There are 4 different bases, A, T, C, G, and they’re very specific about who they pair with:
Adenine with Thymine and Cytosine with Guanine
These groups are complementary base pairs, and they are joined by weak hydrogen bonds, linking the 2 double helix strands in the middle!
So far, we have only said that DNA codes for proteins. This is not entirely true, because there are two types!
- CODING DNA are the genes the cells read and make proteins from
-NON-CODING DNA are like on-off switches for coding DNA- they control gene expression by telling the cell to use or ignore certain genes.
So to make a protein, there are two stages: TRANSCRIPTION of DNA (in the nucleus) and TRANSLATION (in the cytoplasm):
1. The cell reads the genes to get the amino acid order. But DNA is too big to get out of the nucleus to build the protein so it uses a messenger instead!
2. An enzyme temporarily breaks the weak hydrogen bonds and unzips the double helix
3. Another enzyme called RNA polymerase binds to a non-coding gene in front of the gene it wants. Once here, it uses one side of the double helix as a template to make a copy of the gene, with this new complimentary copy being called mRNA.
4. The mRNA travels out into the cytoplasm and attaches to the site of protein synthesis- an organelle called a ribosome
5.As the ribosome inspects the mRNA, it reads the nucleotide bases in groups of 3 called codons, with one codon coding for one specific amino acid.
6. Then another helper called transfer or tRNA brings 100s to1000s of specific amino acids to the ribosome in the sequence the genes state, which are then linked to make the initial polypeptide.
After protein synthesis, the polypeptide then folds into a specific 3D structure.
But change happens, and when the order of bases changes in our genes, we call this a mutation.
Mutations can, therefore, change proteins through our DNA, but usually, their function is preserved and little difference is seen in our phenotypes.
But rarely if enough of the DNA is changed, the protein’s shape can be altered so much that it can’t do its job, like an enzyme without a working active site!