From Gene to Protein ie: Transcription & Translation

Protein Synthesis: overview One gene-one enzyme hypothesis (Beadle and Tatum) One gene-one polypeptide (protein) hypothesis The linear sequence of DNA determines the sequence of Amino Acids Transcription: synthesis of mRNA under the direction of DNA Translation: actual synthesis of a polypeptide under the direction of mRNA Difference in types of cells: Prokaryotes- DNA not segregated from ribosomes. Transcription & Translation occurs in rapid succession Eukaryotes- mRNA is modified and translocated to the cytoplasm for translation

The Triplet Code Xn = number of amino acids that can be coded for…. The genetic instructions for a polypeptide chain are ‘written’ in the DNA as a series of 3-nucleotide ‘words’ called…. Codons: the basic unit of genetic code Don’t forget! ‘U’ (uracil) replaces ‘T’ in RNA Xn = number of amino acids that can be coded for…. where X= # of bases ; n=bases per codon For life on Earth: 43 = 64

Transcription: Only one strand of DNA is transcribed: “The Template Strand” RNA polymerase: pries DNA apart and hooks RNA nucleotides together from the DNA code Promoter region on DNA: where RNA polymerase attaches and where initiation of RNA begins Terminator region: sequence that signals the end of transcription Transcription unit: stretch of DNA transcribed into an RNA molecule

Transcription continued… Initiation~ transcription factors mediate the binding of RNA polymerase II to an initiation sequence (TATA box) Elongation~ RNA polymerase continues unwinding DNA and adding nucleotides to the 3’ end.. Uses ATP this time! Termination~ RNA polymerase reaches terminator sequence… signals the RNA polymerase to stop transcription and release the mRNA

Transcription: overview See Campbell animations!!! D:\bc_campbell_biology_7\0,7052,3117225-,00.html

mRNA modification D:\bc_campbell_biology_7\0,7052,3117225-,00.html 1) 5’ cap: modified guanine; protection; recognition site for ribosomes 2) 3’ tail: poly(A) tail (adenine); protection; recognition; transport 3) RNA splicing: exons (expressed sequences) kept,introns (intervening sequences) spliced out; spliceosome D:\bc_campbell_biology_7\0,7052,3117225-,00.html

Translation mRNA from nucleus is ‘read’ along its codons by tRNA’s anticodons at the ribosome Each codon on the mRNA has a complimentary … tRNA anticodon (nucleotide triplet) Each tRNA has been previously linked to an amino acid using the enzyme… “Aminoacyl-tRNA-synthetase” Wobble: the ability of one tRNA to recognize 2-3 different mRNA codons. Example: CC _ anticodon recognizes GGC, GGA, GGG, and GGU but all code for Glycine. “Redundancy not Ambiguity!”

Translation continued Ribosome: made of rRNA) site of mRNA codon & tRNA anticodon coupling P site holds the tRNA carrying the growing polypeptide chain A site holds the tRNA carrying the next amino acid to be added to the chain E site discharged tRNA’s

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

Translation See Campbell/YouTube animations!! D:\bc_campbell_biology_7\0,7052,3117225-,00.html http://www.youtube.com/watch?v=41_Ne5mS2ls this one is EPIC!

Mutations: genetic material changes in a cell Point mutations…. Changes in 1 or a few base pairs in a single gene Base-pair substitutions: Silent mutations no effect on protein Missense mutations ∆ to a different amino acid (different protein) Nonsense mutations ∆ to a stop codon and a nonfunctional protein Base-pair insertions or deletions:additions or losses of nucleotide pairs in a gene; alters the ‘reading frame’ of triplets~frameshift mutation Mutagens: physical and chemical agents that change DNA. Examples include: Radiation…or Base Analogs McGrawHill