It is DNA that contains the genetic code that is used to make proteins. In turn, it is the structure of proteins that determines many of the biological functions and physical characteristics of an organism.
Genes are segments of DNA. DNA stands for deoxyribose nucleic acid. DNA is made of smaller building blocks called nucleotides. Each nucleotide consists of a deoxyribose sugar, a phosphate group, and a nitrogen base. There are four kinds of nitrogen bases in DNA. DNA’s nitrogen bases are adenine, thymine, cytosine, and guanine. The order of the nucleotides determines the gene that an individual will have.
Genes are transcribed and then translated to form proteins. Transcription and translation, the two processes of protein synthesis, are explained below.
During transcription, the two strands of DNA unwind. One of the strands serves as a template for make an mRNA strand. Each set of three nucleotides on an mRNA is called a codon. These codons will be important in the second phase of protein synthesis called translation. After the mRNA is created during transcription, it migrates to the cytoplasm via a nuclear pore.
During translation, mRNA, ribosomes, rRNA, tRNA, and amino acids come together to make the protein strand.
Once in the cytoplasm, the mRNA and ribosomes attach. The ribosomes serve as scaffolds that match the codons on mRNA’s to the anticodons on the tRNA’s. Anticodons are sets of three nucleotides on the base of a tRNA that are complementary to mRNA codons. On the top of the tRNA are amino acids.
As the ribosome moves down the mRNA during translation, additional tRNA anticodons are matched with the complementary mRNA codons. In this way, amino acids that form a protein are arranged in the correct order. When two amino acids are adjacent to one another, a peptide bond forms. The polypeptide chain continues to grow until a stop codon is reached.
At this point, the polypeptide chain is released from the mRNA strand. The polypeptide chain then forms into a primary, secondary, tertiary, and/or quaternary structure that give the protein its specific function within the cell and organism.