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Protein Synthesis: Transcription How is mRNA created from DNA? Chromosome DNA Gene • Protein Synthesis is when DNA’s code is used by the cell to make proteins. This is also known as gene expression. • The genes “express themselves” when the proteins they code for are made. • IMPORTANT VOCABULARY: – GENE – BASE TRIPLET – CODON – ANTICODON – AMINO ACID – PROTEIN Gene Expression GENE: sequence of DNA that codes for a protein and thus determines a trait BASE TRIPLET: nucleotide triplet on DNA CODON: nucleotide triplet on mRNA that codes for a specific amino acid ANTICODON: nucleotide triplet on tRNA that pairs with a codon AMINO ACIDS: amino acids make up proteins PROTEIN: biomolecule made up of a chain of amino acids Sections within a gene Start Triplet Codes for protein TAC Stop Triplet ATT, ATC, or ACT Base Triplets Examples ATC CCG Overall Process of Protein Synthesis (Gene Expression) Transcription DNA Translation mRNA Protein Transcription Translation Protein DNA contains made the bycode mRNA forand all traits/ tRNA mRNA isismade by copying DNA’s code for proteins a proteinis “deciphered” to build a Information protein. Information in DNA is “rewritten” as a molecule of mRNA TRANSCRIPTION TRANSCRIPTION: mRNA is made copying DNA’s code Occurs in the nucleus Makes mRNA from DNA template click to play animation TRANSCRIPTION G G C A T C C G T A 1. The enzyme helicase break the hydrogen bonds between the nitrogen bases, unzipping a gene portion of the DNA. A TRANSCRIPTION G G G C A T C C A T T 1. (continued) a gene portion of the DNA strand separates A G G G C A T C C A T T A TRANSCRIPTION T A G C A T C G G C A T 2. mRNA is made from the DNA template The enzyme RNA polymerase brings in mRNA nucleotides and matches them with their DNA complement Base Pairing Rule mRNA nucleotides match by the base pairing rule. U A A G G T C A G G C A T C G C A - T (RNA has U) C-G T A A A G G C T C C A A G G T U T A U T A A A T G G C mRNA DNA C A A G G T C C G U T A A editing) leaves the nucleus G G C A T C G A G C 3. mRNA separates from DNA and (after C T G A A A G G C C A A G G T C T G C T A U T A A C C 4. The two DNA strands move back together and….. G T G G C A T G G C A T C C G T A 4. …an enzyme helps the DNA strands rezip. T A REVIEWING TRANSCRIPTION TRANSCRIPTION: mRNA is made copying DNA’s code 1. DNA unzips 2. mRNA is made from the DNA template 3. mRNA separates from DNA and (after editing) leaves the nucleus 4. The DNA molecule rezips (closes back up.) click to play animation mRNA Editing Pre-mRNA is processed to remove noncoding segments introns come out! exons = coding segments introns = non-coding segments inbetween sequence (junk) intron = noncoding (inbetween) sequence eukaryotic DNA exon = coding (expressed) sequence RNA splicing enzymes snRNPs snRNA intron exon Spliceosome 5' Enzyme that recognizes introns and removes them exon 3' spliceosome 5' 3' cut & paste enzyme lariat 5' mature mRNA exon 5' 3' exon 3' excised intron More mRNA editing Need to protect mRNA on its trip from nucleus to cytoplasm enzymes in cytoplasm attack mRNA so we need to protect the ends of the molecule add 5 GTP cap add poly-A tail longer tail, mRNA lasts longer 3' A mRNA 5' G P P P Now mRNA is ready to leave the nucleus! 3' A mRNA 5' G P P P TRY THIS! Transcribe this segment of DNA: TACAACCGATGA Predict the corresponding amino acids for each codon. AUG UUG GCU ACU