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Decoding the Genetic Blueprint: From Gene Mutation to Protein Synthesis

Explore key concepts in protein synthesis, transcription process, and the central dogma of molecular biology. Learn about gene mutations, codon translation, transcription steps, and RNA processing in eukaryotic cells. Discover how genetic information is encoded and decoded to form proteins.

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Decoding the Genetic Blueprint: From Gene Mutation to Protein Synthesis

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  1. Transcription Protein Synthesis: Ch 17

  2. One Gene – One protein • In 1902, Archibald Garrod described the inherited disorder alkaptonuria as an "inborn error of metabolism." He proposed that a gene mutation causes a specific defect in the biochemical pathway for eliminating liquid wastes. The phenotype of the disease — dark urine — is a reflection of this error. • (from DNA from the Beginning)

  3. Beadle & Tatum • Investigated bread mold • Found that mutated bread mold could not produce essential nutrients,and would die. • However, if the mutated mold was provided with a specific supplement, the mold could grow. • Each mutant was defective for a particular gene, so they concluded that the function of the gene was to determine the production of a particular enzyme.

  4. Central Dogma of Molecular Biology How are genes connected to proteins?

  5. Triplet code Codon –a triplet - made of 3 consecutive nucleotides – found on mRNA each codon codes for a specific amino acid 20 amino acids – 64 codons (3 are STOP codons) Codons are read in the 5  3 direction along mRNA Determined from triplet on DNA (complementary)

  6. The reading frame is critical for codons: • i.e. “The fat cat ate the wee rat” • Vs. “Thefatcatatet hew eer at”

  7. Transcription • mRNA is transcribed from DNA Downstream = direction of transcription

  8. Steps for Transcription • Initiation • RNA polymerase binds to promoter • Prokaryotes – direct binding • Eukaryotes- transcription factors bind first, then RNA polymerase • The promoter is a specific sequence of DNA where the RNA polymerase attaches (includes a TATA box)

  9. Steps for Transcription • Elongation • RNA polymerase untwists DNA, read from 3’-5’, elongates mRNA from 5’-3’ • RNA nucleotides have ribose instead of deoxyribose, and uracil instead of thymine • NTPs are used, so cleavage of two phosphates powers transcription

  10. Steps for Transcription • Termination • When terminator sequence in DNA is reached, the transcribed terminator (in RNA) signals the end • Prokaryotes – stops at end of termination signal • Eukaryotes –transcribes a polyadenylation sequence that codes for the polyadenylation signal (AAUAAA) • The pre mRNA is cut about 10-35 nucleotides past AAUAAA sequence

  11. Transcription videos • http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter3/animation__mrna_synthesis__transcription___quiz_1_.html • http://www.dnalc.org/resources/3d/12-transcription-basic.html

  12. Eukaryotic – RNA processing • Eukaryotes modify pre-mRNA before it leaves the cytoplasm • Pre -mRNA – the immediate product of RNA polymerase in eukaryotes

  13. Alteration of mRNA ends • GTP cap – A modified guanosine triphosphate is added to the 5’ end • (also known as a “methyl cap”, 7-methylguanylate cap) • Poly (A) tail – 50-250 adenine nucleotides added to 3’ end • Functions for both: • Helps mRNA leave nucleus • Protects mRNA from degradation • Help ribosomes attach to 5’ end, once mRNA in cytoplasm

  14. mRNA processing • http://www.youtube.com/watch?v=YjWuVrzvZYA

  15. RNA splicing • Pre mRNA has • Introns – intervening sequences • Exons – expressed sequences • The introns are removed and the exons are spliced together • Spliceosome – does the cutting & splicing • Made of snNRP- small nuclear ribonucleoproteins + larger proteins

  16. Alternative splicing • A single gene can code for more than one kind of polypeptide • Depends on what segments are treated as exons during RNA splicing

  17. mRNA splicing • http://www.hhmi.org/biointeractive/mrna-splicing • http://www.youtube.com/watch?v=aVgwr0QpYNE

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