Molecular Basis for Genotype-Phenotype Relationship: DNA Transcription, RNA Translation, and Protein Function

1. Molecular Basis for Relationship between Genotype and Phenotype genotype DNA DNA sequence transcription RNA translation amino acid sequence protein function phenotype organism

2. Cotranscriptional Processing of RNA State of phosphorylation of CTD determines the type of proteins that can associate with the CTD (thus defining cotranscriptional process). 5’ end of pre-mRNA is capped with 7-methylguanosine. This protects the transcript from degradation; capping is also necessary for translation of mature mRNA. Refer to Figure 8-13 from Introduction to Genetic Analysis, Griffiths etal., 2015.

3. Cotranscriptional Processing 3’ end of the transcript typically contains AAUAAA or AUUAAA. This sequence is recognized by an enzyme that cleaves the newly synthesized transcript ~20 nucleotides downstream. At the 3’ end, a poly(A) tail consisting of 150 - 200 adenine nucleotides is added. Polyadenylation is another characteristic of transcription in eukaryotes.

4. Complex Patterns of Eukaryotic RNA Splicing Refer to Figure 8-14 from Introduction to Genetic Analysis, Griffiths etal., 2015. Different mRNA can be produced; different a-tropomyosin can be produced. Alternative splicing is a mechanism for gene regulation. Gene product can be different in different cell types and at different stages of development.

5. Intron Splicing: Conserved Sequences exons - coding sequences introns - noncoding sequences Small nuclear ribonucleoprotein particles (snRNPs) recognize consensus splice junction sequence of GU/AG. snRNPs are complexes of protein and small nuclear RNA (snRNA). Several snRNPs comprise a spliceosome. Spliceosome directs the removal of introns and joining of exons.

6. Spliceosome Assembly and Function Spliceosome interacts with CTD and attaches to pre-mRNA. snRNAs in spliceosomes direct alignment of the splice sites. One end of conserved sequence attaches to conserved adenine in the intron. The “lariat” is released and adjacent exons are joined. Refer to Figure 8-16 from Introduction to Genetic Analysis, Griffiths etal., 2015.

7. Reactions in Exon Splicing Refer to Figure 8-17 from Introduction to Genetic Analysis, Griffiths etal., 2015.

8. Self-Splicing Reaction RNA molecules can act somewhat like enzymes (ribozymes). In the protozoan Tetrahymena, the primary transcript of an rRNA can excise a 413-nucleotide intron from itself. These self-splicing introns are an example of RNA that can catalyze a reaction. Refer to Figure 8-18 from Introduction to Genetic Analysis, Griffiths etal., 2015.

9. Colinearity of Gene and Protein genotype DNA DNA sequence transcription RNA translation amino acid sequence protein function phenotype organism

10. Molecular Basis for Relationship between Genotype and Phenotype genotype DNA DNA sequence transcription RNA translation amino acid sequence protein function phenotype organism

11. tRNA Refer to Figure 9-6 from Introduction to Genetic Analysis, Griffiths etal., 2015. Anticodon of a tRNA molecule recognizes and pairs with an mRNA codon. tRNA contains modified bases: pseudouridine, methylguanosine, dimethylguanosine, methylinosine, dihydrouridine.

12. Genetic Code

13. Aminoacyl-tRNA Synthetase Attaches Amino Acid to tRNA Aminoacyl-tRNA synthetase catalyzes the formation of “charged” tRNA. There is an aminoacyl-tRNA synthetase for each amino acid. The carboxyl end of an amino acid is attached to the 3’ end of the tRNA. Refer to Figure 9-7 from Introduction to Genetic Analysis, Griffiths etal., 2015.

14. Wobble Position Some tRNA molecules can recognize and pair with more than one specific codon. Base-pairing between the 3’ base of a codon and 5’ base of an anticodon is not always exact. Refer to Figure 9-9 from Introduction to Genetic Analysis, Griffiths etal., 2015.