Protein synthesis is a fundamental biological process through which cells produce proteins, the workhorses of the cell involved in virtually every cellular function.
This process is guided by the genetic information encoded in DNA and involves two main stages: transcription and translation.
Transcription
Location: Takes place in the nucleus.
Process
The enzyme RNA polymerase binds to the DNA at a specific site called the promoter, initiating the unwinding of the DNA helix.
RNA polymerase synthesizes a complementary mRNA strand using the DNA template (adenine pairs with uracil, and cytosine pairs with guanine).
The newly formed mRNA undergoes processing, including the addition of a 5' cap and a 3' poly-A tail.
The processed mRNA is then transported to the cytoplasm for the next stage.
Translation
Location: Occurs in the cytoplasm on ribosomes.
Process
Ribosomes read the mRNA sequence in sets of three nucleotides (codons), each specifying an amino acid.
Transfer RNA (tRNA), with its attached amino acid, recognizes specific codons via its anticodon and pairs with the mRNA.
The ribosome catalyzes the formation of peptide bonds, linking amino acids into a polypeptide chain.
Translation continues until a stop codon is reached, signaling the completion of the polypeptide.
The polypeptide then undergoes folding and modifications to become a fully functional protein.
Function of Proteins
Proteins play crucial roles in:
Structural support (e.g., in cells and tissues).
Acting as enzymes to speed up biochemical reactions.
Transporting molecules across cell membranes.
Involvement in cell signaling and immune defense.
The function of a protein is determined by its 3D structure, which is dictated by its amino acid sequence, directly linking genes to protein function.