Describe how the information in DNA is used during transcription and translation to construct polypeptides, including the roles of: • RNA polymerase • messenger RNA (mRNA) • codons • transfer RNA (tRNA) • anticodons • ribosomes

The process of constructing polypeptides from the information in DNA involves two main stages: transcription and translation. Each component plays a crucial role in these processes. Here’s a detailed description of how DNA information is utilized to synthesize polypeptides:

Transcription

1. RNA Polymerase:
   • Role: RNA polymerase is the enzyme that initiates and carries out the transcription process. It binds to the DNA at the promoter region, unwinds the DNA double helix, and synthesizes a complementary RNA strand.
   • Process: RNA polymerase moves along the template strand of the DNA, adding ribonucleotides (A, U, C, G) complementary to the DNA template (A pairs with U in RNA, and C pairs with G).
2. Messenger RNA (mRNA):
   • Role: mRNA is the product of transcription. It serves as a temporary copy of the genetic information encoded in DNA and carries this information from the nucleus (in eukaryotes) to the cytoplasm, where protein synthesis occurs.
   • Process: The mRNA strand is synthesized in the 5′ to 3′ direction and contains codons, which are sequences of three nucleotides that correspond to specific amino acids.

Translation

3. Codons:
   • Role: Codons are the three-nucleotide sequences found in mRNA that specify which amino acid will be added to the growing polypeptide chain. Each codon corresponds to a specific amino acid or a start/stop signal for translation.
   • Process: The sequence of codons in the mRNA dictates the order of amino acids in the polypeptide.
4. Transfer RNA (tRNA):
   • Role: tRNA molecules are responsible for bringing the appropriate amino acids to the ribosome during translation. Each tRNA has a specific amino acid attached and a complementary sequence called an anticodon.
   • Process: tRNAs recognize codons in the mRNA by base pairing their anticodons with the corresponding codons. This ensures that the correct amino acid is added according to the genetic code.
5. Anticodons:
   • Role: Anticodons are three-nucleotide sequences on tRNA that are complementary to the codons on mRNA. This complementary pairing is crucial for accurate translation.
   • Process: When a tRNA’s anticodon pairs with an mRNA codon, it positions the attached amino acid in the correct location for incorporation into the polypeptide chain.
6. Ribosomes:
   • Role: Ribosomes are the molecular machines that facilitate the translation of mRNA into a polypeptide. They consist of rRNA and proteins and have two subunits (large and small).
   • Process:
     • The small subunit of the ribosome binds to the mRNA and scans for the start codon (AUG).
     • The large subunit then assembles, and translation begins. The ribosome moves along the mRNA, reading the codons one at a time.
     • As each codon is read, the corresponding tRNA brings the appropriate amino acid, which is then added to the growing polypeptide chain through peptide bonds.

Summary of the Process

1. Transcription:
   • RNA polymerase synthesizes mRNA from the DNA template.
   • mRNA carries codons that correspond to specific amino acids.
2. Translation:
   • Ribosomes read mRNA codons.
   • tRNA brings amino acids to the ribosome, matching their anticodons to mRNA codons.
   • Amino acids are linked together to form a polypeptide chain.

This coordinated process ensures that the genetic information encoded in DNA is accurately translated into functional proteins, which perform a variety of roles in the cell and organism.