Lecture on Transcription and Translation

Overview

• Transcription: Process where DNA is converted into mRNA (messenger RNA).
• Translation: Process of converting information in mRNA to build a protein.
• Ribosome: Organelle where protein synthesis occurs.

Transcription

• Steps: Initiation, Elongation, Termination.

Initiation

• RNA Polymerase: Binds to promoter region of DNA (TATA box in eukaryotes).
• Promoter Region: Sequence TATAA, located 25 nucleotides upstream of transcription start.

Elongation

• RNA Polymerase: Separates DNA strands, adds nucleotides to growing mRNA strand.
• Direction: Synthesizes mRNA 5' to 3', reads DNA 3' to 5'.
• Template Strand: Also called anti-sense strand, used for mRNA synthesis.
• Non-template Strand: Also called sense or coding strand.

Termination

• Separation: RNA polymerase, mRNA strand, and DNA template separate.
• Poly A Polymerase: Adds a poly-A tail to the 3' end of mRNA.
• 5' Cap: Added to protect mRNA from degradation.

RNA Splicing

• Introns: Non-coding sequences, removed.
• Exons: Coding sequences, remain and are used for protein synthesis.

Practice Problem

• Creating mRNA from a DNA sequence by matching nucleotides.
• G pairs with C; A pairs with U (Uracil in RNA), T pairs with A.

Translation

• Process: Using mRNA to construct proteins in the cytosol.
• tRNA (Transfer RNA): Matches codons with specific amino acids.

Steps: Initiation, Elongation, Termination

Initiation

• Start Codon (AUG): Pairs with anticodon UAC on tRNA.
• Methionine: First amino acid attached to tRNA entering the ribosome at P site.

Elongation

• tRNA Entry at A Site: New tRNA enters A site.
• Peptide Bond Formation: Between amino acids on tRNA at P site.
• Movement: tRNA moves from P to E site, loses amino acid, polypeptide chain grows.

Termination

• Stop Codons: UAA, UAG, UGA cause termination.
• Release Factor: Enters at A site, causing ribosomal subunits to disassemble.

Post-Translation

• Golgi Body: Proteins undergo folding and modification to perform specific functions.

Conclusion

• Overview of transcription and translation processes, emphasizing key steps and components involved.