Summary
Highlights
Protein synthesis is the process of making proteins, divided into two main steps: transcription and translation. Transcription involves copying a gene from DNA into messenger RNA (mRNA), while translation uses this mRNA to produce a protein.
DNA, located in the nucleus, contains genes with specific base sequences that code for proteins. However, DNA is too large to leave the nucleus. Ribosomes, where proteins are made, are outside the nucleus. Therefore, a smaller copy, mRNA, is needed to carry the genetic information from the nucleus to the ribosomes.
mRNA is a copy of a single gene. It is shorter than DNA, single-stranded, and contains uracil (U) instead of thymine (T). These structural differences allow mRNA to exit the nucleus and bind to ribosomes.
Transcription begins when RNA polymerase binds to the DNA before a gene. The DNA strands separate, exposing the bases. RNA polymerase then moves along the DNA's template strand, reading bases and adding complementary RNA bases (A with U, T with A, G with C, C with G) to form an mRNA strand. The DNA re-coils behind the polymerase. Once the entire gene is copied, RNA polymerase detaches, and the mRNA is free to leave the nucleus.
Before translation, it's important to understand that every three bases (a triplet or codon) on DNA and mRNA code for a specific amino acid. There are 20 different amino acids, each with a unique three-base codon.
Translation occurs at the ribosome where the mRNA strand binds. Transfer RNA (tRNA) molecules carry specific amino acids and have an anticodon that is complementary to a codon on the mRNA. The ribosome moves along the mRNA, and tRNA molecules bring the corresponding amino acids in the correct order. The ribosome joins these amino acids, forming a growing chain. Once a tRNA delivers its amino acid, it detaches and can be reused. This process continues until a complete chain of amino acids is formed, which then detaches and folds into a protein.