The body synthesizes protein through a process where amino acids are linked together, forming a polypeptide chain. This process is also known as protein translation.
The Fundamental Reaction: Peptide Bond Formation
The key to protein synthesis is the formation of a peptide bond. This bond is created between:
- The carboxyl group (-COOH) of the last amino acid in a growing polypeptide chain.
- The free amino group (-NH2) of a new, incoming amino acid.
This reaction occurs step-by-step, effectively adding amino acids to the chain one at a time. According to the provided reference, protein synthesis proceeds from the N-terminal end to the C-terminal end. This means that the first amino acid added to the chain (the N-terminus) remains at the beginning, and the last amino acid added (the C-terminus) forms the end of the polypeptide.
Step-by-Step Process Summary:
- Transcription: DNA's genetic code for a specific protein is copied into messenger RNA (mRNA).
- Translation: The mRNA moves to ribosomes, the cellular machinery where proteins are made.
- Initiation: The ribosome binds to the mRNA, marking the starting point for protein synthesis.
- Elongation: As the ribosome moves along the mRNA, transfer RNA (tRNA) molecules carrying specific amino acids enter the ribosome based on the mRNA sequence. Peptide bonds form between the amino acids, adding each new amino acid to the growing polypeptide chain.
- Termination: The process stops when a stop codon on the mRNA is reached.
- Folding & Modification: The polypeptide chain folds into its specific three-dimensional shape, often with the help of other proteins called chaperones. It may also undergo further modifications such as glycosylation.
Key Players in Protein Synthesis:
| Player | Role |
|---|---|
| DNA | Contains the genetic code for proteins. |
| mRNA | Carries the genetic code from DNA to ribosomes. |
| tRNA | Transports specific amino acids to the ribosome according to the mRNA code. |
| Ribosomes | Cellular organelles where protein synthesis occurs. |
| Amino Acids | The building blocks of proteins. |
| Peptide Bonds | Chemical bonds that link amino acids together, forming a polypeptide chain. |
Example:
Imagine building a LEGO structure.
- The DNA is the instruction manual.
- The mRNA is a copied page of instructions.
- The tRNA molecules are workers carrying individual LEGO bricks (amino acids).
- The ribosome is the construction site, assembling the LEGO bricks based on the instructions.
- The peptide bonds are the links that hold the bricks together forming a specific LEGO shape which is the final protein.
In summary, the body synthesizes proteins by creating peptide bonds between amino acids, adding each amino acid sequentially based on genetic information carried by mRNA, at the ribosome, forming a polypeptide chain from the N-terminus to C-terminus. This process occurs in distinct phases: transcription, translation, initiation, elongation, and termination, resulting in the final protein.
