Protein Synthesis: Transcription How is mRNA created from DNA?

Chromosome DNA Prentice Hall Biology textbook Gene

IMPORTANT VOCABULARY: 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 Stop Triplet Start Triplet Codes for protein TAC ATT, ATC, or ACT Base Triplets Prentice Hall Biology textbook Examples ATC CCG

Overall Process of Protein Synthesis (Gene Expression) DNA Transcription Translation mRNA Protein DNA contains the code for all traits/ proteins Translation Protein is made by mRNA and tRNA Information is “deciphered” to build a protein. Transcription mRNA is made by copying DNA’s code for a 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 A G C A T C G 1. The enzyme helicase break the hydrogen bonds between the nitrogen bases, unzipping a gene portion of the DNA.

TRANSCRIPTION A T 1. (continued) a gene portion of the DNA strand separates A T G C G C A T G C

A T G C A T C G

TRANSCRIPTION 2. mRNA is made from the DNA template G T 2. mRNA is made from the DNA template The enzyme RNA polymerase brings in mRNA nucleotides and matches them with their DNA complement A G C A G

Base Pairing Rule mRNA nucleotides match by the base pairing rule. A - T (RNA has U) C - G A T C G U T G C A

U T A A A T G G C C A A T G G C

A T C G U T A G mRNA DNA C A G

3. mRNA separates from DNA and (after editing) leaves the nucleus

G A C U T A T C G A G C A G

4. The two DNA strands move back together and…..

4. …an enzyme helps the DNA strands rezip. G C A T C G 4. …an enzyme helps the DNA strands rezip.

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 non- coding segments exons = coding segments introns = non-coding segments inbetween sequence (junk) introns come out! intron = noncoding (inbetween) sequence eukaryotic DNA exon = coding (expressed) sequence 22

RNA splicing enzymes Spliceosome snRNPs exon intron snRNA 5' 3' Spliceosome Enzyme that recognizes introns and removes them cut & paste enzyme spliceosome exon excised intron 5' 3' lariat mature mRNA 23

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 A 3' poly-A tail mRNA 5' 5' cap 3' G P 50-250 A’s eukaryotic RNA is about 10% of eukaryotic gene. 24

Now mRNA is ready to leave the nucleus! 3' poly-A tail mRNA 5' 5' cap 3' G P 50-250 A’s

TRY THIS! TACAACCGATGA Transcribe this segment of DNA: You can have them do this on white boards or in their notes. If you are using the interactive notebook this will go on the left page.

Predict the corresponding amino acids for each codon. AUG UUG GCU ACU