Presentation is loading. Please wait.

Presentation is loading. Please wait.

N Chapter 17~ From Gene to Protein. Protein Synthesis: overview n One gene-one enzyme hypothesis (Beadle and Tatum) n One gene-one polypeptide (protein)

Similar presentations


Presentation on theme: "N Chapter 17~ From Gene to Protein. Protein Synthesis: overview n One gene-one enzyme hypothesis (Beadle and Tatum) n One gene-one polypeptide (protein)"— Presentation transcript:

1 n Chapter 17~ From Gene to Protein

2 Protein Synthesis: overview n One gene-one enzyme hypothesis (Beadle and Tatum) n One gene-one polypeptide (protein) hypothesis n Transcription: synthesis of RNA under the direction of DNA (mRNA) n Translation: actual synthesis of a polypeptide under the direction of mRNA

3 The Triplet Code n The genetic instructions for a polypeptide chain are written in the DNA as a series of 3-nucleotide words n Codons n U (uracil) replaces T in RNA

4 Transcription, I n RNA polymerase: pries DNA apart and hooks RNA nucleotides together from the DNA code n Promoter region on DNA: where RNA polymerase attaches and where initiation of RNA begins n Terminator region: sequence that signals the end of transcription n Transcription unit: stretch of DNA transcribed into an RNA molecule

5 Transcription, II n Initiation~ transcription factors mediate the binding of RNA polymerase to an initiation sequence (TATA box) n Elongation~ RNA polymerase continues unwinding DNA and adding nucleotides to the 3 end n Termination~ RNA polymerase reaches terminator sequence

6 Transcription: overview

7 mRNA modification n 1) 5 cap: modified guanine; protection; recognition site for ribosomes n 2) 3 tail: poly(A) tail (adenine); protection; recognition; transport n 3) RNA splicing: exons (expressed sequences) kept,introns (intervening sequences) spliced out; spliceosome

8 Translation, I n mRNA from nucleus is read along its codons by tRNAs anticodons at the ribosome n tRNA anticodon (nucleotide triplet); amino acid

9 Translation, II n rRNA site of mRNA codon & tRNA anticodon coupling n P site holds the tRNA carrying the growing polypeptide chain n A site holds the tRNA carrying the next amino acid to be added to the chain n E site discharged tRNAs

10 Translation, III n Initiation~ union of mRNA, tRNA, small ribosomal subunit; followed by large subunit n Elongation~ codon recognition peptide bond formation translocation n Termination~ stop codon reaches A site n Polyribosomes: translation of mRNA by many ribosomes (many copies of a polypeptide very quickly)

11 Translation

12 Mutations: genetic material changes in a cell n Point mutations…. n Changes in 1 or a few base pairs in a single gene n Base-pair substitutions:silent mutations no effect on proteinmissense to a different amino acid (different protein)nonsense to a stop codon and a nonfunctional protein n Base-pair insertions or deletions: additions or losses of nucleotide pairs in a gene; alters the reading frame of triplets~frameshift mutation n Mutagens: physical and chemical agents that change DNA


Download ppt "N Chapter 17~ From Gene to Protein. Protein Synthesis: overview n One gene-one enzyme hypothesis (Beadle and Tatum) n One gene-one polypeptide (protein)"

Similar presentations


Ads by Google