BIOL 213 1st Edition Lecture 19 Outline of Last Lecture I. Somatic cells and gametesII. The five basic types of genetic change that contribute to evolutiona. Mutation within a geneb. Gene duplicationc. Gene deletiond. Exon shufflinge. Horizontal gene transferIII. Gene duplicationa. Gene familiesIV. Genome duplicationV. Exon shuffling can result in the appearance of eukaryotic genesVI. Transposable elements can change genes by inserting new coding sequencesa. Can transpose exonsVII. Horizontal gene transfera. Plasmids VIII. The human genomeIX. Comparative genomics X. Overview a. Gene duplicationb. Exon shufflingThese 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.c. Transposable elementsd. Horizontal gene transferOutline of Current LectureI. The fate of proteins after synthesis – compartmentalizationII. Protein sortinga. Necessary and sufficientIII. Transport through nuclear poresIV. Transport across membranesa. Mitochondria and chloroplastb. ER membranei. Soluble proteinsii. Transmembrane proteinsV. Transport by vesiclesa. Highly specific Current LectureI. The fate of proteins after synthesis – compartmentalization a. After proteins are translated, they must be transported throughout the cell and sometimes outside of the cellb. Each protein has a specific target location c. This is called compartmentalizationd. Eukaryotes are compartmentalized by their membrane bound organellesCompartment Main functionCytosol Metabolic pathways, protein synthesisNucleus Contains main genome, DNA/RNA synthesisER Synthesis of most lipids, protein distributionGolgi Protein and lipid modification for distributionLysosomes Intracellular degradationEndosomes Sorting of endocytosed materialsMitochondria ATP synthesis – oxidative phosphorylationChloroplasts Photosynthesis Peroxisomes Oxidation of toxic compounds – contains peroxide II. Protein sortinga. Each protein must have a signal sequence of amino acids on its end that is unique to the organelle to which it needs to be transportedi. These sequences are necessary and sufficient for protein sorting1. Necessary: they are needed; the proteins will not be sorted without them2. Sufficient: they are all that is needed; the proteins don’t need anything else to be sortedb. There are three main energy-dependent ways in which a protein is transferred from the cytosol into an organellec. Transport through nuclear poresi. Seen in the nucleusd. Transport across membranese. Transport by vesiclesIII. Transport through nuclear poresa. The nucleus has two membranesb. These pores allow molecules through both membranesc. These pores have fibril molecules on both sides of the membrane to prevent unwanted materials from diffusing throughi. The fibril molecules on the nuclear side create a nuclear “cage” that catchunwanted materialsd. Small molecules can diffuse through the pores without any helpe. But proteins are too big to diffuse by themselves – they are transported by helper proteinsi. They need the appropriate sorting signal sequence: nuclear localization signal1. This is a short stretch of lysines and arginines that are positively chargedii. They are helped by nuclear transport receptors (helper proteins)iii. When a protein with the correct signal sequence approaches the nucleus,a nuclear transport receptor will bind to itiv. The two proteins will move through the nuclear pore into the nucleusv. Once inside the nucleus, a Ran-GTP binds to the nuclear transport receptor, causing the transported protein to be released inside the nucleusvi. The Ran-GTP-nuclear transport receptor complex travels back outside the nucleusvii. The complex is GTP hydrolyzed (this is the energy input that causes this kind of transport to be active) and the now Ran-GDP and nuclear transport receptor dissociateviii. The Ran-GDP travels back into the nucleusix. The nuclear transport receptor is ready to transport another proteinf. This transport is active – energy input is requiredi. GTPg. The proteins stay completely folded during the transportationIV. Transport across membranesa. Mitochondrial and chloroplasti. The signal sequence of the protein binds to the receptor protein that is integrated in the mitochondrial/chloroplast membraneii. The receptor protein diffuses through the membrane until it comes in contact with a pore that spans across both membranesiii. The protein will unfold as it goes through the pore because the pore is so smalliv. Once it’s inside the mitochondria/chloroplast, chaperonins refold it1. They refold it so that it has a specialized function specific to the organelle2. When it’s in the cytosol, it doesn’t have a specific function because it’s folded differentlyv. The signal sequence is cleaved so that the protein is now matureb. ERi. Most proteins that are inside the ER lumen are to be transported outside the cellii. These are synthesized into the lumeniii. After they are in the lumen, the proteins can be stabilized by disulfide bridges between two cysteines1. This is because the ER lumen is an oxidizing environment whereas the cytosol is a reducing environment2. The oxidizing environment will cause the sulfur to bind to a sulfur atom instead of a hydrogen atom3. The sulfur atom is more electronegative than the hydrogen, causing the sulfur to be oxidizediv. Soluble proteins1. When a ribosome reaches the signal sequence during protein synthesis, a signal-recognition particle (SRP) will bind to the signal sequence, causing the ribosome to stop synthesizinga. The signal sequence is at the end of a polypeptide chain of a soluble protein2. The SRP will bind to an SRP receptor in the ER membrane, which isnext to a translocation channel3. The SRP will transfer the polypeptide chain to the channel and then dissociate4. The signal sequence will remain in the channel and the ribosome will continue to synthesize the protein through the channel and into the lumen so that a loop of polypeptide chain forms within the lumen5. Once the protein is complete the signal sequence will be cleaved by signal peptidase causing it to stay in the channel while the protein moves completely into the lumen v. Transmembrane proteins1. When a ribosome reaches the signal sequence during protein synthesis, a signal-recognition particle (SRP) will bind to the signal sequence, causing the ribosome to stop synthesizinga. The signal sequence is in the middle of a polypeptide