1. Gene Expression

2. What is Gene Expression?  Expression can be defined as: –Shown –Manifested –Articulated We can determine a person’s genes by what is shown or seen in their body.

3. What is Gene Expression?  Genes contain the specific information for our body  They are instructions for making proteins  Proteins make us: –look the way we do –function the way we do –develop and grow the way we do –behave the way we do –think the way we do

5. What is Gene Expression?  All cells within an organism have the same DNA, but not all genes are expressed. –Example: a neuron (nerve cell) will express genes necessary for nerve function.  Therefore, some genes are active (or expressed) in some cells and some genes are inactivated

7. How are genes expressed?  With the help of RNA

8. Making Proteins Step One = Transcription Step Two = Translation

9. Transcription 1.Initiation: DNA section with desired gene (the yellow strand) is unzipped by RNA polymerase (the green triangle) 2.Elongation: RNA polymerase adds complementary nucleotides, mRNA strand is made (torquoise strand) 3.Termination: when a stop sequence is reached, mRNA separates from DNA and DNA is re-zipped

10. RNA Processing  Before leaving the nucleus: –1. Introns are removed or spliced - “junk DNA” –2. Exons (“expressed”) are put back together –3. mRNA leaves the nucleus  See page 204 (fig. 8.26) in your text for more info

11. Codon  3 letter sequence on mRNA  Carries code for amino acid from DNA Anti-codon  3 letter sequence on tRNA  Complimentary to mRNA codon

12. 1.Initiation: Ribosome finds the first codon of the gene on mRNA (It’s ‘AUG’ for every gene!) 2.Elongation: ribosome shifts down to next codon; tRNA brings in next amino acid, repeats 3.Termination: ribosome reaches a “stop” codon, protein is released Translation

13. Animations  Transcription Transcription  Translation Translation

14. How does the cell determine what amino acid goes with the mRNA’s codon? CODON = AUG Start in the center and work your way out A U G Amino acid is methionine Try finding the amino acid for the codon ‘CUA’LEUCINE Decoder Chart #1 –

15. REVIEW MAKE SURE YOU KNOW THE FOLLOWING!  What gene expression means  4 Differences between DNA and RNA  3 Types of RNA and their functions  Codon and Anticodon  How mRNA is processed  Steps of Transcription  Steps of Translation  How to use the ‘decoder chart’(s)