Gene Activity

1. Gene Activity 1 Link between genotype & phenotype Unique structures Amino acid sequence Specific enzyme Structures in organisms Proteins DNA specifies proteins Development Particular organism DNA nucleotide sequence

2. George Beadle & Edward Tatum 2 Minimal media No minimal media 1 3 2 C D B 1 defective enzyme Neurospora crassa Diploid & haploid individuals Normal haploid spores Mutate by X-ray Required enriched media Mutants could not complete metabolic pathway A Mutant could grow if supplemented with C & D 1 defective gene One gene – One Enzyme

3. Linus Pauling & Harvey Itano 3 Change in protein structure Electrophoresis HbA HbS HbA HbA HbS HbS HbA HbS Mutation Does HBS have a different structure than HBA ? Charge difference + - Mutation leads to change in protein structure

4. Vernon Ingram 4 ( - ) glutamate Nonpolar valine Low O2 HbS stacks into long, semi-rigid rods 2 Polypeptides -  and  Gene for each type What are structural differences between HbA & HbS HbA HbS Hydrophobic Less soluble Precipitate Sickle Push against plasma membrane Hemoglobin Only  chain affected One gene – One polypeptide

5. Gene 5 Bring about formation of protein Instructions Proteins Many sets of 3 nucleotides Code for sequence of RNA nucleotides RNA molecules Proteins are polymers of amino acids Structural elements Biological activity Genes Development Metabolism Genetic code 3 DNA nucleotides contain the code for 1 amino acid Gene Triplets

6. DNA vs. RNA 6 Sugar Deoxyribose Ribose Bases A = T G = C A = U G = C Strands Single Double No Yes Helix Size Huge Small Location Nucleus & cytoplasm Nucleus 3 nucleotides Triplet Codon Anticodon

7. Classes of RNA 7 Messenger RNA mRNA Take message from DNA in nucleus to cytoplasm Ribosomal RNA rRNA Ribosome subunits – rRNA & protein component Transfer RNA tRNA Transfers amino acids to the ribosomes Ribosome Binding sites for mRNA and 2 tRNA’s Facilitate complementary base paring mRNA codon & tRNA anticodon

8. Marshall Nirenberg & Heinrich Matthei 8 Polymer of uracil Synthesize polypeptide One amino acid 43 Produced synthetic RNA Cell-free system Phenylalanine RNA with 3 nucleotides Assign each amino acid a 3-nucleotide codon RNA Every possible combination of codons 3 nucleotides = 1 codon 4 x 4 x 4 = 64 4 different nucleotides

9. mRNA Codons 9 20 amino acids 64 codons >1 codon per AA Degenerate Protective against mutations Unambiguous each codon has only 1 meaning Start & stop signals Pg 241

10. Protein Synthesis 10 Ribosomes in cytoplasm Instructions to cytoplasm Message mRNA Codon Cytoplasm mRNA Amino acids to the ribosome DNA in the nucleus Transcription: (nucleus) DNA triplet code RNA polymerase mRNA Translation: (cytoplasm) Ribosomes Link amino acids Order dictated by mRNA tRNA Anticodon

11. DNA Triplets (orders to build) mRNA Codons (message) Cytoplasm -aug -phe -asp tRNA- -ser -ala ala tRNA- phe tRNA- asp tRNA- ser tRNA- aug Transcription Ribosomes (builders) Translation 11

12. Begin Transcription 12 Transcription factors binds Promoter RNA polymerase produces complementary mRNA Start codon Binding attracts RNA polymerase DNA double helix Terminator - Stop codon

13. Transcription of DNA 13 RNA polymerase triplet sense strand codon RNA polymerase “reads” the DNA sense strand Every 3 nucleotides of mRNA forms a CODON RNA T - A A - U G - C C - G Forms primary transcript – complements DNA

14. Primary Transcript Cap 5 Poly A tail 3 Rejoined Modified into mature transcript Each end is altered: Modified guanine Binding site for ribosomes 150-200 adenines Transports mRNA out of nucleus Inhibits degradation Transcript is altered Introns are removed: DNA that is never expressed Exons – expressed Spliceosome - Complex of ribonucleoproteins Ribozymes - RNA w/enzymatic activity 14 Prokaryotes

15. Genetic Code 15 3 nucleotides contain a code for 1 amino acid Triplet - 3 nucleotides in DNA Codon - 3 nucleotides in mRNA Compliment the triplet Anticodon - 3 nucleotides in tRNA Compliment the codon

16. Translation – 2nd Step 16 Ribosome translates the mRNA into AA chain Dehydration synthesis

17. tRNA 17 Binding site 3 complementary nucleotides Codon tRNA synthatase AA activating enzyme Single strand RNA H-bonds Cloverleaf Anticodon mRNA

18. rRNA - Produced from DNA template in nucleolus Packaged w/proteins into subunit Move to cytoplasm Subunits combine into active ribosome rRNA is a ribozyme Joins amino acids together Translation terminates @ polypeptide completion Subunit fall off mRNA Polyribosome - Several ribosomes attach along mRNA Multiple polypeptides formed 18

19. Translation 19 1st step - Initiation Initiation factors Small subunit binds mRNA at start codon Initiator tRNA pairs with start codon Methionine Large subunit binds at start codon 2nd step - Elongation Elongation factors Facilitate complementary base pairing AA added one at a time to polypeptide chain 3rd step - Termination Release factor Cleaves polypeptide from last tRNA at stop codon Ribosome separates & polypeptide is released

20. Sense DNA TAC – GTC – GAA – CAA – GTG - ATT 20 DNA Polymerase RNA Polymerase ATG - CAG - CTT - GTT - CAC- TAA DNA Replication Triplets AUG - CAG - CUU - GUU - CAC - UAA mRNA Codons Nucleus Transcription tRNA UAC GUC GAA CAA GUG AUU Anticodons Met Glu Leu Val His Stop Amino acids Cytoplasm Translation