DNA Transcription and Translation
Overview
- Aim: Understand how DNA codes for organisms via transcription and translation
- Process: Conversion of genetic code into proteins by enzymes
Key Concepts
Chromosomes and Genes
- Chromosome: Long DNA molecule with millions of base pairs
- Genes: Segments of DNA coding for specific proteins
- Size: Between 10k to 50k base pairs (human average), longest ~2.5 million base pairs
- Expression: Protein production from a gene
Transcription
- Purpose: Produce messenger RNA (mRNA) from DNA
- Enzyme: RNA polymerase, aided by transcription factors
- Process:
- Initiation: RNA polymerase binds to a promoter sequence, separates DNA strands
- Elongation: Template strand (antisense) read from 3' to 5' to synthesize mRNA from 5' to 3'
- Use ribose and uracil instead of deoxyribose and thymine
- Similar to DNA replication but mRNA is produced, and DNA re-zips as RNA polymerase moves
- Termination: RNA polymerase detaches, DNA returns to original state, mRNA is produced
- Post-Transcription: mRNA undergoes modifications, exits nucleus to cytoplasm
Translation
- Purpose: Convert mRNA code into a protein
- Location: Ribosome in cytoplasm
- Components: mRNA, ribosomes, transfer RNA (tRNA), amino acids
- Process:
- Initiation: Small ribosomal subunit binds mRNA and initiator tRNA at start codon (AUG – methionine)
- Elongation: tRNAs enter ribosome carrying amino acids, codon and anticodon pairing occurs, polypeptide chain grows
- Termination: Reaches stop codon, completed polypeptide released for folding/modifications
- Codons: Triplets of RNA bases
- Determine amino acids via genetic code table
- Start Codon: AUG
- Stop Codons: Three codons terminate translation
Significance
- Proteins: Responsible for muscle, organ tissues, receptors, and enzymes
- Genetic Code: Basis for living organisms
Conclusion
- Transcription and translation convert DNA into functional proteins
- Essential for the development and functioning of organisms
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