Protein Synthesis and Role of mRNA in Eukaryotic Cells

Overview of mRNA Function

• mRNA (messenger RNA) carries genetic instructions from DNA to ribosomes.
• It facilitates protein production by guiding the ribosomes to assemble amino acids.

Ribosomes

• Eukaryotic cells can contain several million ribosomes.
• Ribosomes are complex catalytic machines essential for assembling proteins.

Structure of Ribosomes

• Composed of two subunits: one large and one small.
• mRNA passes through the ribosome similar to a computer tape.

Role of tRNA

• Amino acids are transported to ribosomes by transfer RNAs (tRNA).
• tRNAs are larger green molecules, compared to the small glowing red amino acids.

Reading Genetic Code

• Small subunit of the ribosome positions mRNA to be read in codons (groups of three letters).
• Each mRNA codon pairs with a corresponding anti-codon on a tRNA molecule.

Protein Assembly Process

1. A-Site Binding
   • tRNA enters the ribosome at the A-Site for codon/anti-codon matching.
2. P-Site Shift
   • Correct tRNA is moved to the P-Site.
   • Attached amino acid is added to the growing protein chain.
   • mRNA is ratcheted forward by one codon (three nucleotides).
3. E-Site Ejection
   • Spent tRNA moves to the E-Site and is ejected for recycling.

Protein Synthesis

• As the mRNA is translated, the amino acid sequence is elongated.
• Finished protein chain emerges from the ribosome and folds into its functional shape.
• Protein shape is determined by the sequence and order of amino acids.

Central Dogma of Molecular Biology

• Describes the flow of genetic information: DNA → RNA → Protein.
• The 4-letter DNA code is translated into the structure and function of proteins.