3.18B: Describe the Stages of Protein Synthesis including Transcription and Translation, Including the Role of mRNA, Ribosomes, tRNA, Codons and Anticodons

TRANSCRIPTION: Synthesis of mRNA transcript copied from DNA template by RNA polymerase

TRANSLATION: Synthesis of Proteins with Amino acid sequence determined by base sequence of mRNA transcript

TRANSCRIPTION

Diagram showing the Process of Transcription

EXPLANATION: For Protein synthesis to occur, DNA template needs to be copied to synthesize an mRNA transcript by RNA Polymerase via Transcription Transcription occurs in the Nucleus, where there are free Nucleotides with one of the four bases (Adenine, Uracil, Guanine, and Cytosine) Transcription begins with RNA Polymerase binding to unwind and unzip the two DNA strands As result, RNA Polymerase will present the free Nucleotides to form complementary base pairs via Hydrogen bonds to synthesize an mRNA transcript s If RNA Polymerase presents Nucleotide with incorrect base, Nucleotide will break away  s However, if RNA Polymerase presents Nucleotide with complementary base to DNA strand, they will bind to form complementary base pairs via Hydrogen bonds  s This continues until RNA Polymerase reaches the end of DNA strand, causing mRNA transcript to peel away and exit the Nucleus through the Nuclear pore RNA Polymerase will detach from DNA strand, and DNA strand will rewind to original state (double helix)

TRANSLATION

Diagram showing the Process of Translation

EXPLANATION: For Protein to be synthesised, mRNA transcript needs to be translated to synthesise amino acid sequence that forms specific Protein Translation occurs in the Cytoplasm, where tRNA molecules carrying specific Amino acid have an anticodon site (triplets of bases on tRNA) Translation begins with Ribosome binding to mRNA transcript As a result, Ribosome exposes the start codon (triplets of bases on mRNA) on mRNA transcript, causing initiator tRNA molecule (carrying an Amino acid) with complementary anticodon to bind to it via Hydrogen bonds Ribosome will expose the next codon on mRNA transcript, resulting in another tRNA molecule (carrying an Amino acid) with complementary anticodon to bind to it via Hydrogen bonds The two Amino acids carried by tRNA molecule will then start to form a Polypeptide chain that will lengthen via the formation of Peptide bonds Used tRNA molecule breaks away to exit Ribosome and collect another Amino acid This process continues until stop codon on mRNA transcript is exposed in Ribosome, causing the release of Polypeptide chain into Cytoplasm to be further modified to form a specific Protein