BIO 172 1st Edition Lecture 8 Outline of Last Lecture I. mRNA ProcessingII. TranslationOutline of Current Lecture I. Posttranslational modificationsII. ChaperonesIII. EnzymesCurrent LecturePost Translational Modifications:5’un translated region is part of exon 1. That stays in the mRNA! 3’ un translated region also stays in mRNA.UTR: has ribosome binding site and recognizes AUG to bring in methionine (eukaryotes) or Formal Met (prokaryote).UTR = un-translated region. The portion of the mRNA outside of the coding sequence.Intron: portion of primary transcript removed from the mature mRNA (processed transcript).(introns do NOT contain coding sequences – except in case of alternative splicing)Exon: portion of primary transcript that is retained in mature mRNA.(exons contain both coding sequences and UTR sequences)Features of Translation: polypeptides synthesized from amino terminus (Nitrogen base) to their carboxyl terminus.mRNA is “read” by ribosomes from the 5’ end to the 3’ end.A single mRNA can be translated many times by ribosomes; multiple ribosomes can simultaneously translate the same mRNA. One mRNA can have multiple starting and stopping codons, so that strand can be translated many times.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.The polypeptide produced from translation often must be modified before it is a functional protein.In Prokaryotes, mRNA is often polycictronic:Monocistronic mRNA- from start to stop codon makes one protein!Eukaryotes: one promoter sequence allows transcription of several genes. Several different proteins, from several different genes, can come from one mRNA. Good for regulating cellular processes because if the proteins and functions are related, they can all function together as an operon… all encoded on same mRNA, so the levels will be the same for all the proteins.Post Translational Modifications of Polypeptides:The polypeptide is transferred to its appropriate cellular destination.Proper folding of the polypeptide.Addition of phosphate, lipid, and carbohydrate groups to a protein. Some environmental signal might need to be bound to a protein for a modification to occur. The signal finds a molecule, and goes through a process of post translational modification (because, for example, the protein needed to be phosphorylated for the protein to carry out its function…)REVIEW: four levels of protein structure!Primary: sequence of amino acids linked by peptide bonds.Secondary: atoms in the backbone interact. Hydrogen bonds help hold either the Alpha Helix or Beta Pleated Sheet together. The protein is folded or coiled.Tertiary: One polypeptide chain with one or more secondary structures! Overall folded shape of a polypeptide. Stabilized by many different bonds, between atoms in R groups:hydrogen bonds, Hydrophobic (C-H packed densely, van der waals), Ionic association, disulfide (covalent) bonds.Quaternary: shape of a complex of multiple polypeptide chains, held together by covalent, ionic, hydrogen, and/or hydrophobic interactions. Two tertiary structures come together to form a functional protein.Denaturation: Loss of Protein ConformationProteins denature if exposed to Heat, pH changes, or chemicals.Chaperones inhibit denaturation.*re-naturation is possible for only some proteins, with the help of chaperones.-Denaturation is bad, because the protein loses its coiled shape. -Can destabilize some of the bonds that help the protein keep its shape… if exposed to heat, or if the pH changes or chemicals break the non-covalent bonds, the protein will unfold.-Sometimes they can renature…. And adopt their original structure if a chaperone protein comes in to help! Unfortunately, sometimes nothing can renature protein.Chaperones are proteins that assist with folding other proteins!The chaperone creates a sheltered environ-ment to allow proteins to adopt specific con-figurations.Chaperones help with one of the biggest problems denatured proteins (or partially unfolded or fully unfolded proteins) face, by not allowing the protein to fold on itself or bond with hydrophobic regions of it.The chaperone protein itself has quaternary structure. Chaperone aids in protein folding!Cap protein (the orange or tan colored “cap” in the above diagram) must be part of chaperone complex to be fully active structure. This holds the protein inside the chaperone.Chaperone- supposed to prevent areas of a protein from interacting if they shouldn’t. For example, the protein doesn’t want two alpha helices binding together. So the chaperone should help when a protein needs to be refolded. Because an unfolded protein can go inside… and the protein can begin to fold properly. The chaperone prevents some of the hydrophobic interactions from happening. The chaperone is an environment where the protein will not fold prematurely. IF its not blocked, the protein would remake itself as an aggregate which would not be the appropriate manner to promote protein function.In the diagram below: Acid causes proteins to unfold, and since no chaperones exist, the conditions of stress on cells means the cells die.Potential Energy: stored in an object.Kinetic Energy: energy of motion includes motion at the molecular state.Work may be mechanical, chemical, kinetic (heat) energy. Kinetic energy of molecular motion is also called thermal energy. High potential energy at top of waterfall lowers as the water molecule falls.An example of humans jumping off a pier into water:Potential energy = energy that is stored and could be used to do work. So standing on the pier, ready to jump into the water.Conversion of potential to kinetic energy: when you are falling/diving into the water.Kinetic energy = energy you have mid-jump.Least amount of potential energy when you are in the water.Conversion of Kinetic energy to have more potential energy: people in the water who need to climb the stairs in order to be back up on the pier, to have potential energy. Have to use kinetic energy (muscles) to get up in order to have a lot of potential energy.FREE ENERGY: energy that can be used to do work. Objects move from high free energy to low. Cells use free energy to do work!The change in free energy amounts in a cell determines reaction characteristics!SPONTANEOUS, ENERGY RELEASING REACTIONS: EXERGONIC (work), EXOTHERMIC (heat). Here spontaneous does not refer to speed- it