RNA Molecules and RNA Processing Functions and Modifications of RNA Molecules

DNA Information Flow From DNA initial transcript RNA transcription Protein translation replication processing mature RNA

Types of RNA Produced by Transcription Messenger RNAMessenger RNA Contains the code words for the sequence of amino acids in a specific protein CODON = group of three nucleotides acting as a code word for an amino acid CODON = group of three nucleotides acting as a code word for an amino acid

Arrangement of Codons on mRNA

Types of RNA Produced by Transcription Transfer RNATransfer RNA –“Translates” the message by bringing a specific amino acid into the correct position on the growing protein chain –Has ANTICODON = a group of three nucleotides on a tRNA that recognizes a mRNA codon –Has amino acid attachment site anticodon

Types of RNA Produced by Transcription Ribosomal RNARibosomal RNA One of the structural components of the ribosome One of the structural components of the ribosome Ribosome = organelle where protein synthesis occurs Ribosome = organelle where protein synthesis occurs Has sites to bind both mRNA and tRNA Has sites to bind both mRNA and tRNA

Interrupted Genes Eukaryotic Genes have interruptions within regions coding for protein intron = interrupting sequence exon = portion of coding region Processing of the pre-mRNA is required to remove introns and join exons. intron 1 intron 2 Exon 1 Exon 2 Exon 3 Coding Region Exon 1 Exon 2 Exon 3 Translated to Produce Protein

mRNA Processing DNA Add 5’ cap Remove Introns Splice Exons together together Cleave at 3’ end Add 3’ poly-A tail Transcription Pre mRNA Mature mRNA leaves for cytoplasm In nucleus 5’3’ intron 1 intron 2 Exon 1 Exon 2 Exon 3 m7 G-P-P-P- intron 1 intron 2 Exon 1 Exon 2 Exon 3 AAAAAA….. m7 G-P-P-P- intron 1 intron 2 Exon 1 Exon 2 Exon 3 AAAAAA…… m7 G-P-P-P- Exon 1 Exon 2 Exon 3 Start Codon Stop Codon Untranslated Region (UTR) UTR with consensus sequence Protein-coding Region

Applying Your Knowledge Which of the following molecules lacks introns? 1.Pre-mRNA 2.DNA 3.Mature messenger RNA 4.All of these lack introns 5.None of these lack introns

Intron Removal for Ovalbumin mRNA

Addition of a 5’-Methyl Guanine Cap

Cleavage and Polyadenylation of 3’ end 1.Pre-mRNA is cleaved nucleotides downstream of the AAUAAA consensus sequence. (Rat1 will attach to 5’ end to terminate transcription.) Adenine nucleotides are added enzymatically to the resulting 3’ end.

Identifying Sites for Intron Removal

Steps in Splicing

Alternative Splicing

Multiple 3’ Cleavage Sites

RNA Editing

Applying Your Knowledge A poly-A tail (repeating sequence of adenine nucleotides) is added to _____ of the primary transcript. 1.The 3’ end 2.The 5’ end 3.Either the 3’ end or the 5’ end 4.Both the 3’ end and the 5’ end 5.Neither the 3’ end nor the 5’ end

Applying Your Knowledge Which molecule contains the information for assembling the amino acids in the correct order in the protein? 1.rRNA 2.tRNA 3.mRNA 4.All of these 5.None of these

tRNA Processing CleavageSplicing Nucleotide Addition Nucleotide Modification

rRNA Processing

RNA Interference (RNAi) Process by which small RNA molecules regulate gene expressionProcess by which small RNA molecules regulate gene expression Types of small RNAsTypes of small RNAs –Micro RNAs (miRNAs) –Small Interfering RNAs (siRNAs) Protein componentsProtein components –Dicer –Protein + RNA = RISC (RNA-Induced Silencing Complex)

Producing Small RNAs

Interfering with RNA Function

Interfering with DNA Function Some siRNAs can inhibit transcriptionSome siRNAs can inhibit transcription Protein componentsProtein components –Protein + RNA = RITS (RNA-Induced Transcriptional Silencing) –Methylating Enzyme Changes the chemical characteristics of DNA or chromatin histone proteins to silence transcriptionChanges the chemical characteristics of DNA or chromatin histone proteins to silence transcription siRNAs

From different RNA molecules

Gene Silencing by RNA Interference Extra genes for a protein involved in pigment production were introduced into petunia plants. Silencing of both the native and newly-introduced genes led to white flower coloration. Extra genes for a protein involved in pigment production were introduced into petunia plants. Silencing of both the native and newly-introduced genes led to white flower coloration.

Processes Affected by RNAi Genomic “Immunity”- protection from viral and transposon genes observed in plants and invertebratesGenomic “Immunity”- protection from viral and transposon genes observed in plants and invertebrates Regulation of gene expression related toRegulation of gene expression related to –Development --miRNAs involved in the timing of morphogenesis and maintenance of stem cell populations –Cell fate and proliferation –Cancer –Cell death