Translation

Translation Overview

  • Date: 10/27/2025

  • Topic Subject: Biochemicals washing up on beaches, with a focus on nucleotides.

Learning Objectives

  • Describe the process of translation and understand the implications if any component of this process is absent.

  • Determine protein sequences when provided with corresponding DNA sequences.

The Central Dogma of Molecular Biology

  • Processes:

    • Transcription

      • Purpose: RNA synthesis

      • Location: Nucleus

    • Translation

      • Purpose: Protein synthesis

      • Location: Cytoplasm at ribosome

  • Flow of Information:

    • DNA → RNA → Protein

  • Key Points:

    • DNA serves as the original blueprint for protein synthesis.

    • mRNA (messenger RNA) is synthesized as a copy of a specific gene found on a DNA molecule.

    • mRNA exits the nucleus to be read by ribosomes, which assemble amino acids into proteins based on the mRNA sequence.

Converting mRNA to Protein

  • Function of mRNA: Carries information essential for protein construction.

  • Translation Process: Occurs on ribosomes where mRNA information is decoded into a linear sequence of amino acids, forming a polypeptide chain that later folds into a functional protein.

The Central Dogma and Genetic Information Flow

  • Genetic Information Flow:

    • Pattern: DNA → RNA → Protein

  • Base Pairing for Amino Acids:

    • 4 basic nucleotide units are used in DNA/RNA.

    • 20 basic amino acids are synthesized in proteins.

  • Base Pair Coding:

    • 1 amino acid is typically coded by a triplet (3 bases) in mRNA

Codons and the Genetic Code

  • Overview of Codons:

    • Consists of 64 mRNA codons (triplets).

    • Encodes for 20 amino acids used in protein synthesis.

    • Codon Definition: Sequence of three mRNA nucleotides that specifies a particular amino acid.

  • Redundancy in Genetic Code:

    • Certain amino acids can be represented by multiple codons, allowing degeneracy in genetic coding.

  • Reading Direction:

    • mRNA is read from its 5' end to 3' end.

  • Key Codons:

    • Start Codon: AUG (Methionine - Met) indicates the commencement of translation.

    • Stop Codons: UAA, UAG, UGA signal the termination of translation.

Codon Table and Amino Acid Associations

  • Codon Examples and Corresponding Amino Acids:

    • | Codon | Amino Acid |
      |-------|------------------|
      | UUU | Phenylalanine (Phe) |
      | UCU | Serine (Ser) |
      | UAU | Tyrosine (Tyr) |
      | UGU | Cysteine (Cys) |
      | UUC | Phenylalanine (Phe) |
      | UAA | Stop |
      | UAG | Stop |
      | UGA | Stop |
      | AUG | Methionine (Met) |
      | AUA | Isoleucine (Ile) |
      | CUG | Leucine (Leu) |
      | AUG | Start Codon |

  • Example Codon Queries:

    • What amino acid corresponds to the codon CCG? Answer: Proline (Pro)

    • What codon is designated for lysine (Lys)? Answers: AAA or AAG

Reading Frames and Their Implications

  • Reading Frames:

    • There are three potential reading frames, dependent on the starting point of translation on the mRNA strand.

  • Illustrative Example:

    • Sequence: 5′ CAC GGU CGA UGA GGU UAC AUA AC… 3′

      • Frame 1: Reads starting from the first nucleotide

      • Frame 2: Starts from the second nucleotide

      • Frame 3: Begins from the third nucleotide

    • Note: Each reading frame can produce a drastically different protein sequence owing to the triplet coding scheme.