Protein Synthesis

Protein Synthesis Overview

• Protein synthesis is the process by which cells make proteins, following the instructions contained within genes.
• Protein synthesis takes place in two main stages: transcription and translation.

Transcription

• Transcription is the first stage of protein synthesis. It occurs in the nucleus of the cell.
• In transcription, a section of DNA containing a gene unwinds and unzips.
• The DNA sequence of the gene is then copied into a molecule of messenger RNA (mRNA).
• The mRNA molecule detaches from the DNA and leaves the nucleus through its pores.

mRNA Molecule

• The mRNA molecule is smaller than DNA and can therefore move out of the nucleus and into the cytoplasm.
• The mRNA molecule carries the genetic code from the DNA to the ribosomes.

Translation

• Translation is the second stage of protein synthesis, occurring at the ribosomes in the cytoplasm.
• The ribosome reads the sequence of codons (three-base sequences) on the mRNA molecule.
• Each codon specifies or ‘codes for’ a particular amino acid.

Role of tRNA

• During translation, each codon on the mRNA molecule attracts a complementary transfer RNA (tRNA) molecule carrying a specific amino acid.
• The tRNA molecules attach their amino acids in the correct order to form a polypeptide chain.
• The polypeptide chain folds into a specific shape to form a protein.

Protein Folding and Function

• The final structure and therefore function of the protein is determined by the specific sequence of amino acids, coded for by the DNA and mRNA sequences.
• Proteins play numerous roles in organisms, serving as enzymes, forming structural components of tissues, and functioning in the immune response.