Protein Synthesis


Transcription and Translation

Process of building proteins

Transcription: The DNA unwinds and "unzips" in the area of the gene. Enzymes match RNA nucleotides to the unzipped nitrogen bases of the gene, forming a single strand of mRNA.
2. The strand of mRNA detaches from the gene and goes out of the nucleus through one of the pores in the nuclear envelope. The DNA zips back together and winds back up.
3. The mRNA finds a ribosome where protein synthesis will happen.

4. Each set of 3 bases on the mRNA is called a codon. Each codon calls for a specific amino acid to be brought to the building site. The first codon is always AUG, so it is called the start codon.
5. In the cytoplasm are molecules of tRNA. On one end of a tRNA molecule is the anticodon: a set of three bases that will match a certain codon. The other end of the tRNA can pick up and hold a certain amino acid. Each tRNA can only hold one kind of amino acid.
6. A tRNA with an anticodon that matches whichever codon is in place on the ribosome The codon and anticodon fit together like two pieces of a jigsaw puzzle. Since the first codon is AUG, the first anticodon must have the matching bases UAC. (Memory trick: AU match like in AUstralia; CG match and they both are round letters.)

8. The amino acid brought by the first tRNA bonds to the amino acid brought by the second tRNA. The first tRNA is free to go, and the second tRNA stays in place for now.
9. Steps 7 and 8 repeat until finally they come to an mRNA codon that is the STOP codon. At this point the amino acid chain breaks off, folds up, and the protein is ready to use.

Transcription: the tRNA which has anticodons puts the corresponding nucleotides onto the mRNA strand.