Describe the process of protein biosynthesis.

1. 1 · Open in two lines. Protein biosynthesis turns the genetic message in DNA into a protein. DNA is transcribed into mRNA, which ribosomes translate into a chain of amino acids.
2. 2 · Draw the ribosome at work. [Diagram: mRNA on the ribosome with E, P and A sites; tRNA anticodons pairing with codons; growing peptide chain]
3. 3 · Transcription in brief. RNA polymerase copies DNA into mRNA in the nucleus; capping, poly-A tail and splicing; mRNA moves to the cytoplasm.
4. 4 · Translation in four stages.
   • Activation: aminoacyl-tRNA synthetase and ATP load each tRNA.
   • Initiation: AUG, Met-tRNA, initiation factors, 80S ribosome.
   • Elongation: EF-1 brings the aminoacyl-tRNA, peptidyl transferase makes the bond, EF-2 moves the ribosome.
   • Termination: stop codon; release factors free the chain.
5. 5 · Modification and the genetic code.
   • Folding, trimming, phosphorylation, glycosylation, hydroxylation, carboxylation.
   • Code: triplet, degenerate, universal, non-overlapping; AUG start, three stops.
6. 6 · Significance. Makes every enzyme, hormone and structural protein. Many antibiotics (tetracycline, streptomycin) work by blocking bacterial translation.
7. 7 · Nutrition link. All essential amino acids must be available together; vitamins C and K are needed for key modifications.
8. 8 · Close in one line. Sum up: DNA → mRNA → protein, at a cost of 4 high-energy bonds per peptide bond.

Scoring tip: Number the stages clearly and name the factor or enzyme at each. The energy count is an easy extra mark.