Translation Bio1090

Chapter 1: Introduction to Translation

• Overview of Translation

  • Translation is the second part of the central dogma, converting RNA into protein.

  • It follows the RNA synthesis discussed in previous lectures.

• RNA Synthesis Recap

  • RNA is synthesized from DNA templates, with a 5' end transcribed toward the 3' end.

  • The end product is a polypeptide chain.

• Key Components in Translation

  • Messenger RNA (mRNA): Carries the code from DNA for translating into proteins.

  • Transfer RNA (tRNA): Brings amino acids to the ribosome based on the codon sequence.

  • Ribosomal Complex: Composed of ribosomal RNA (rRNA) and proteins, facilitating translation.

  • Release Factors: Involved in terminating translation.

• Eukaryotic vs. Prokaryotic mRNA

  • Eukaryotic mRNA is monocistronic (one gene).

  • Prokaryotic mRNA can be polycistronic (multiple proteins from one RNA).

• Structure of mRNA

  • Contains an untranslated region (5' UTR) before the start codon (AUG).

  • Ends with an untranslated region (3' UTR).

  • The start codon (AUG) signals the beginning of translation, while stop codons signal termination.

Chapter 2: The Genetic Code and Codons

• The Role of the Genetic Code

  • Codons: Triplets of nucleotides in mRNA that specify amino acids.

  • Start Codon: AUG always initiates translation.

• Properties of the Genetic Code

  • No spaces between codons; they are adjacent.

  • Non-overlapping nature: Each nucleotide belongs to one codon.

  • Degeneracy: Most amino acids are encoded by multiple codons (e.g., leucine).

  • Universality: The genetic code is consistent across prokaryotes and eukaryotes.

Chapter 3: Components of Translation

• Major Components

  • mRNA: Template for polypeptide synthesis.

  • tRNA: Transfers specific amino acids to the ribosome.

  • Ribosome: Site of translation with three binding sites for tRNA: A (Acceptor), P (Peptidyl), and E (Exit) sites.

• tRNA Structure

  • Cloverleaf structure with an amino acid attached to the 3' end.

  • Anticodon region pairs with mRNA codon in an anti-parallel fashion.

• Translation Steps

  • Initiation: Start with AUG, tRNA binds to mRNA.

  • Elongation: Additional amino acids are added sequentially.

  • Termination: When the ribosome reaches a stop codon, the polypeptide chain is released.

Chapter 4: Elongation Process in Translation

• Initiation Mechanism

  • tRNA with methionine (Met) attaches at the P site.

• Ribosome Movement

  • Ribosome moves three nucleotides at a time along the mRNA to elongate the polypeptide chain.

• Polypeptide Chain Growth

  • The amino acids are coupled via peptide bonds, forming the chain.

• Completing Translation

  • Stop codons signal termination. No tRNA matches stop codons; releasing factors facilitate disassembly.

Chapter 5: Charged tRNA and Ribosome Function

• Ribosome Structure

  • Composed of large and small subunits; vital for tRNA interaction.

• Translation Cycle

  • Charged tRNA enters the A site, transferring its amino acid to the polypeptide.

  • Uncharged tRNA exits from the E site.

• Elongation Continues

  • The process repeats, with ribosomal subunits advancing along mRNA.

  • Base pairing occurs between mRNA codons and tRNA anticodons.

  • Growing polypeptide's N-terminus and C-terminus are established.

Chapter 6: Conclusion and Mutations

• Significance of Mutations

  • Mutations in DNA can lead to changes in amino acid sequences and protein function.

  • Most mutations are neutral (gibberish), but some may be beneficial or harmful.

• Recap of Central Dogma

  • DNA -> Transcription -> mRNA -> Translation -> Polypeptide.

  • Post-translational modifications may occur, affecting final protein structure.

• Protein Structure and Function

  • Proteins can form various structures (e.g., alpha helices, beta-pleated sheets) based on amino acid composition.

  • Cellular functions of proteins depend on their unique structural configurations.