MTG 23 Post - Intracellular Compartments & Protein Transport PDF

Chapter 15 Intracellular Compartments and Protein Transport April 01 (M) Essential Cell Biology, Fifth Edition Copyright © 2019 W. W. Norton & Company Chapter Contents MEMBRANE-ENCLOSED ORGANELLES PROTEIN SORTING VESICULAR TRANSPORT SECRETORY PATHWAYS ENDOCYTIC PATHWAYS Learning Outcomes To identify...

Chapter 15 Intracellular Compartments and Protein Transport April 01 (M) Essential Cell Biology, Fifth Edition Copyright © 2019 W. W. Norton & Company Chapter Contents MEMBRANE-ENCLOSED ORGANELLES PROTEIN SORTING VESICULAR TRANSPORT SECRETORY PATHWAYS ENDOCYTIC PATHWAYS Learning Outcomes To identify MEMBRANE-ENCLOSED ORGANELLES’ structures and their respective functions To be able to discuss principles, concepts and mechanisms of: – PROTEIN SORTING – VESICULAR TRANSPORT Eukaryotic Cells Contain a Set of Membrane-enclosed Organelles - In eukaryotic cells, internal membranes create enclosed compartments that segregate different metabolic processes. Organelles are held in locations by attachment to cytoskeleton. Endosomes are membrane-bound vesicles formed via a complex family of processes collectively known as endocytosis The size of vesicles varies, and those larger than 100 nanometers in diameter are typically referred to as vacuoles. Smooth ER lacks ribosomes site for steroid hormone synthesis site for detoxification e.g. alcohol detoxification sequesters Ca2+ from the cytosol Organelles occupy nearly half the volume of a eukaryotic cell. Organelles Evolved in Different Ways Nuclear membranes and the ER may have evolved through invagination of the plasma membrane. ORGANELLES EVOLVED IN DIFFERENT WAYS Nuclear membrane, ER, Golgi, endosomes and lysosomes are formed from invaginations of plasma membrane. Endomembrane system = nuclear membrane, ER, Golgi ,endosomes, peroxisomes, lysosomes  These individual membrane systems communicate with each other by means of vesicles budding off from one organelle and then fusing with the next. MEMBRANE-ENCLOSED ORGANELLES EVOLVED IN DIFFERENT WAYS Mitochondria and chloroplasts have their own genome and can make a subset of their proteins. organelles evolved from bacteria that have been engulfed by primitive pre-eukaryotic cells Membrane-enclosed Organelles Evolved in Different Ways MEMBRANE-ENCLOSED ORGANELLES Eukaryotic Cells Contain a Basic Set of Membrane-enclosed Organelles Membrane-enclosed Organelles Evolved in Different Ways – through invagination of the plasma membrane – organelles evolved from bacteria that have been engulfed by primitive pre-eukaryotic cells PROTEIN SORTING as cells grow, membrane enclosed organelles enlarge by incorporation of new molecules the organelles divide then organelles distributed between 2 daughter cells Proteins are being produced not only during cell division but are continually being produced. PROTEIN SORTING For mitochondria, chloroplasts, peroxisomes, nucleus: proteins are directly delivered from the cytosol Golgi, lysosomes, endosomes, inner nuclear membrane: proteins (as well as lipids) are delivered indirectly from the ER – Peroxisomes acquire some of its membrane proteins from ER but majority of its proteins are from the cytosol Proteins Are Transported into Organelles by Three Mechanisms  synthesis of virtually all proteins begins in the cytosol  dispatched to different locations according to specific address labels  labels contained in the amino sequence Essential Cell Biology, Fifth Edition Copyright © 2019 W. W. Norton & Company PROTEINS ARE TRANSPORTED INTO ORGANELLES BY THREE MECHANISMS Sorting signalPores or Nuclear signal sequence is a stretch of amino acids Protein Translocators to direct a protein to a specific destination in Transport Vesicles a cell. Signal Sequences Direct Proteins to the Correct Compartment Hydrophobic amino acids KDEL Basic amino acids SKL Signal Sequences Direct Proteins to the Correct Compartment PROTEINS ENTER THE NUCLEUS THROUGH NUCLEAR PORES Essential Cell Biology, Fifth Edition Copyright © 2019 W. W. Norton & Company Proteins Enter the Nucleus Through Nuclear Pores the double membrane of nuclear envelope is penetrated by nuclear pores proteins are transported in their fully folded conformation and ribosomes as assembled particles Nuclear Localization Signal- sequence that directs a protein from the cytosol into the nucleus contains several positively charged K (lys) or R (arg) The NLS is recognized by nuclear import receptors. Meshwork of proteins- allows small water soluble molecules to pass freely and non selectively The nuclear pore complex forms a gate through which selected macromolecules and larger complexes enter or exit the nucleus. Essential Cell Biology, Fifth Edition Copyright © 2019 W. W. Norton & Company PROSPECTIVE NUCLEAR PROTEINS ARE IMPORTED FROM THE CYTOSOL THROUGH NUCLEAR PORES  The import of molecules in or export of molecules out of the nucleus requires energy.  To be able to identify the steps in nuclear transport ENERGY SUPPLIED BY GTP HYDROLYSIS DRIVES NUCLEAR TRANSPORT. Essential Cell Biology, Fifth Edition Copyright © 2019 W. W. Norton & Company Ran is converted from one The small monomeric conformation to the other with GTPase, Ran, exists in two the help of accessory proteins that are differently localized. conformations the concentration of Ran-GTP is higher in the nucleus Essential Cell Biology, Fifth Edition Copyright © 2019 W. W. Norton & Company Essential Cell Biology, Fifth Edition Copyright © 2019 W. W. Norton & Company PROTEIN SORTING Proteins Are Transported into Organelles by Three Mechanisms Signal Sequences Direct Proteins to the Correct Compartment Proteins Enter the Nucleus Through Nuclear Pores o NLS o Nuclear import/export proteins o GTPase activity (GTP hydrolysis)drives nuclear transport A mitochondrion has an outer and inner membrane, both of which must be crossed for a mitochondrial precursor protein to enter the organelle. Essential Cell Biology, Fifth Edition Copyright © 2019 W. W. Norton & Company PROTEINS UNFOLD TO ENTER MITOCHONDRIA AND CHLOROPLASTS Proteins Unfold to Enter Mitochondria and Chloroplasts signal sequence allows proteins to enter their specific organelle Chaperones aid to pull proteins across membranes. PROTEIN SORTING Proteins unfold to enter mitochondria and chloroplasts. Signal sequences and protein translocators are required for protein transport from cytosol to organelles such as mitochondria, and chloroplast END OF MTG 23 POST