Eukaryotic Transcription Eukaryotic Cells – cells with a nucleus and many organelles Organisms with nucleated cells belong to the largest classification group, Domain Eukaryota Four Kingdoms of Organisms which are eukaryotic are animal, plants, protists and fungi.

Basic Principles of Transcription Transcription is the synthesis of RNA under the direction of DNA Transcription produces messenger RNA (mRNA) In a eukaryotic cell, the nuclear envelope separates transcription from translation Eukaryotic RNA transcripts are modified through RNA processing to yield finished mRNA mRNA is a copy of the genetic code of organism.

Eukaryotic Transcription

Stages of Transcription: Review Q’s Where is the TATAA box located? In which step does the initiation complex form? Transcription factors are associated with which structures in the diagram? Where would the codon AUG be located? Where are the genes to make a polypeptide located? Where is the termination signal located? What unwinds or melts the DNA to allow for transcription What is another name for RNA transcript? Remember, the completed transcript will be modified after it has been synthesized in eukaryotic cell. Protein Synthesis: Eukaryotic Transcription

Concept 17.3: Eukaryotic cells modify RNA after transcription Enzymes in the eukaryotic nucleus modify pre-mRNA before the genetic messages are dispatched to the cytoplasm During RNA processing, both ends of the primary transcript are usually altered Also, usually some interior parts of the molecule are cut out, and the other parts spliced together Exon – coding region and Intron –noncoding region

Make a table like the one below in your notebook Make a table like the one below in your notebook. As you watch the video, complete it with information. Prokaryotic vs Eukaryotic Transcription Characteristic Prokaryotic Cell Eukaryotic Cell Nucleus present Uses a specific type of RNA polymerase Have Ribosomes Location of Transcription DNA contains exons DNA contains introns Modifies mRNA Location Translation

Diagram of Protein Synthesis: Prokaryotic & Eukaryotic Cell LE 17-3-5 DNA TRANSCRIPTION mRNA Ribosome TRANSLATION Polypeptide Prokaryotic cell Nuclear envelope Diagram of Protein Synthesis: Prokaryotic & Eukaryotic Cell TRANSCRIPTION DNA Pre-mRNA RNA PROCESSING mRNA Ribosome TRANSLATION Polypeptide Eukaryotic cell

Prokayotic versus Eukaryotic Proteins Synthesis Larger cell size Nucleus contains DNA and a nucleolus for RNA Ribosome and other organelles Larger size chromosome Linear chromosome Chromosome contains coding and noncoding regions for proteins Smaller cell size No nucleus – nucleoid region for DNA Ribosome only organelle Smaller size chromosome Circular chromosome Chromosome contains only coding regions for proteins

Post-Transcriptional Modification Splicing exons Adding cap & tail 5¢ Exon Intron Exon Intron Exon 3¢ Pre-mRNA 5¢Cap Poly-A tail 1 30 31 104 105 146 Introns cut out and exons spliced together Coding segment 5¢Cap Poly-A tail 1 146 5¢ UTR 3¢ UTR Leaves nucleus – ready go translation

Alteration of mRNA Ends in Eukaryotic Cells Each end of a pre-mRNA molecule is modified in a particular way: The 5 end receives a modified nucleotide cap The 3 end gets a poly-A tail These modifications share several functions: They seem to facilitate the export of mRNA They protect mRNA from hydrolytic enzymes They help ribosomes attach to the 5’ end

Gene DNA Exon 1 Intron Exon 2 Intron Exon 3 Transcription LE 17-12 Gene DNA Exon 1 Intron Exon 2 Intron Exon 3 Transcription RNA processing Translation Exon 2 Polypeptide

RNA transcript (pre-mRNA) Splicesome: structure the cuts out introns. LE 17-11 RNA transcript (pre-mRNA) 5¢ Exon 1 Intron Exon 2 Protein Other proteins snRNA snRNPs Spliceosome Splicesome: structure the cuts out introns. 5¢ Spliceosome components Cut-out intron mRNA 5¢ Exon 1 Exon 2

In some cases, RNA splicing is carried out by spliceosomes Spliceosomes consist of a variety of proteins and several small nuclear ribonucleoproteins (snRNPs) that recognize the splice sites RNA splicing can lead to genetic diversity

Helpful Transcription Animation Links Stages of Transcription: Components Transcription Factors RNA Splicing and Spliceosome RNA Splicing