Protein biosynthesis in cells occurs in two different stages. The first stage is called transcription. It occurs in the cell nucleus and it involves a sequence of DNA being converted into a corresponding piece of RNA that is called messenger RNA (mRNA). The process is performed by the enzyme RNA polymerase. The mRNA produced is complementary to the DNA template it was copied from, meaning that the specific order of the nucleotide base pairing is preserved in the RNA nucleotides. G becomes C and A becomes U (and vice versa).
The second stage of protein biosynthesis is called translation. The mRNA from transcription makes its way to the ribosomes in the cell. While there, the RNA bases are read in groups of three called codons. Each codon codes for a particular amino acid. The amino acids are brought to the ribosome in order by transfer RNA (tRNA) where they are then linked together via amide bonds to produce a polypeptide. The completed polypeptide is folded to become a completed protein.
In brief, transcription is the copying of DNA and transcribbing it into mRNA. Translation is into process making proteins by reading code in the mRNA that is produced during transcription.
During transcription, single stranded mRNA is produced. The bases on the mRNA are complementary to the bases of the DNA, except Uracil is used to pair with Adenine instead of Thymine. Transcription occurs in the nucleus, and the mRNA leaves the nucleus via nuclear pore.
Translation, or protein synthesis occurs in the cytoplasm of the cells. The ribosomes in the cytoplasm read the codons, which are protein codes in a unit of three bases, and attached the corresponding peptide to the growing polypeptide strand. To picture the process, it is important to know that the major players in translation. The ribosome unit attaches to the mRNA and read the codons. The transfer RNA (tRNA) has two ends: one end has an anticodon that would complementary pair with the specific codon on the mRNA; the other end attachs to an amino acid. Basically, the codons on the mRNA signal when to start proteisynthesis, the type of polypeptide, and when to stop translation.
Even though many more combinations of codon that results from diffe rent arrangement of bases, there are twenty different amino acid, single unit of protein. Hence, more than one codon may code for an amino acid.