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Agenda 3/13 • Transcription Notes • Transcription Posters/RNA Processing • Turn in: Worksheets from Friday • Homework: Transcription video and notes, Chp 14 reading/notes 1 Warm Up (In Notes) • Create a list of 10 specific proteins we have studied this year 2 Uses of Proteins 3 What is a gene? • Today the definition for a gene is a sequence of DNA molecules that can direct the synthesis of a molecule product. • Genes do not all code for a protein, but all do code for an RNA molecule. • Some of those RNAs are translated into protein, but many serve other functions, such as gene regulation. 4 Overview of Protein Synthesis • DNA is located in the nucleus • Proteins are made in the cytoplasm • RNA is the intermediate between the DNA code and the actual synthesis of a protein 5 Structure of RNA versus DNA 6 • RNA vs. DNA • RNA DNA • Single stranded Double stranded • Ribose Deoxyribose • U instead T T instead of U • Nucleus and cytoplasm organelles Restricted to nucleus & • Multiple uses Used as template for RNA synthesis and proteins 7 Three Main Types of RNA 8 There are different types of RNA • mRNA-carries the information from the DNA gene to the cytoplasm. Determines the sequence of amino acids for a protein • tRNA-brings the correct amino acid to the ribosome and mRNA in translation • rRNA-found on ribosomes and used to "connect" the tRNA to the mRNA • snRNA-found on spliceosomes. Used to remove introns. • SRP RNA-part of the signal recognition particle used to bring a translating ribosome to the E.R. and threads the emerging polypeptide chain into the lumen of the E.R. 9 Differences in Protein Synthesis between Prokaryotes and Eukaryotes • Prokaryotes do not have introns like eukaryotes. • RNA in prokaryotes does not have to be processed like eukaryotes. • Transcription and translation can be simultaneous in prokaryotes. 10 Genetic Code • Amino acids are coded for by a triplet of DNA nucleotides called a codon. 11 • Come up with 3 different observations about the codon chart 12 Genetic Code • The code has redundancy (What does this mean? • Each codon only codes for one amino acid. • The code is a universal code meaning almost all cells use the same code. A eukaryotic gene can be expressed in a prokaryotic cell. 13 Specifying or Coding for a Polypeptide This gene designates that the following peptide chain be made with the amino acids in this particular order. 14 Transcription Overview Transcription-RNA synthesis from a DNA template • 1. Initiation • 2. Elongation • 3. Termination • (4?) RNA processing 15 Initiation There is a region prior to beginning of a gene where the RNA polymerase attaches called the promoter region. The promoter region determines which side of the gene will be transcribed. In a prokaryotic cell, the RNA polymerase attaches directly to the region In a eukaryotic cell there are transcription factors (proteins) which help facilitate the attachment of the RNA polymerase. 16 Initiation 17 Elongation • Elongation- RNA polymerase unwinds the DNA and base pairs RNA nucleotides to the DNA gene. RNA is made 5′ → 3′ so the DNA gene is 3′ → 5′. 18 Termination RNA synthesis proceeds until the RNA polymerase encounters a sequence that triggers its dissociation. 19 RNA Processing Eukaryotic RNA processing • 5' cap is added. • At the 3' end 30-200 adenine nucleotides are added (poly-A-tail). • Introns are removed 20 Removing Introns • A spliceosome removes the introns. • Spliceosomes are composed of smaller particles called snRNP (made of proteins and snRNA). • The spliceosome will splice the intron at a specific RNA sequence. 21 RNA Processing • Different exons are recombined in different ways for certain mRNAs. This increases the number of different proteins. 22 Exon Shuffling and Different Proteins • Proteins often have a modular architecture consisting of discrete regions called domains • In many cases, different exons code for the different domains in a protein • Exon shuffling may result in the evolution of new proteins. 23 Ready for Translation • This mRNA has been processed and is called mature mRNA. It is ready to go to the cytoplasm for translation. 24 Transcription Posters • Using the template DNA strand and RNA nucleotides, create your strand of mRNA. On your poster also include: – – – – Three steps of transcription The promoter region Draw and label all enzymes involved Depict RNA processing incorporating terms from the reading 25