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80 Cards in this Set
- Front
- Back
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What is Protein Sorting?
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The transfer process of unique set of proteins made in the cytosol to the compartments/organelles in which they're used
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What is the main function of the cytosol?
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Contains many metabolic pathways, where protein synthesis occurs
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What is the main function of the nucleus?
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Contains main genome and synthesizes DNA and RNA
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What is the main function of the ER?
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Synthesis of most lipids, proteins for distribution to many organelles and to the plasma membrane
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What is the main function of the Golgi apparatus?
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Modification, sorting, and packaging of proteins and lipids for either secretion or delivery to other organelles
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What is the main function of Lysosomes?
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Intracellular degradation
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What is the main function of Endosomes?
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Sorting of endocytosed material
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What is the main function of mitochondria?
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ATP synthesis by oxidative phosphorylation
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What is the main function of chloroplasts?
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ATP synthesis and carbon fixation by photosynthesis
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What is the main function of peroxisomes?
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oxidation of toxic materials
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The nucleus is surrounded by what?
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double membrane called nuclear envelope
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How does the nucleus communicate with the cytosol?
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Via nuclear pores that perforate the envelope
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What is the Rough ER?
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Area of the ER where ribosomes are attached
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The Rough ER has ribosomes on its surface that actively synthesize proteins that are delivered where?
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To the ER lumen or ER membrane
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Where is the site of steroid hormone synthesis?
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Smooth ER in adrenal glands
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Where are a variety of organic molecules like alcohol detoxified?
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In the smooth ER of liver cells!
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What are Peroxisomes?
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Small organelles with single layer that contain enzymes used in a variety of oxidative reactions that break down lipids and toxic molecules.
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What organelle is most present, by number, in a cell?
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Mitochondria!
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The nuclear membranes and the membranes of the ER, Golgi apparatus, endosomes, and lysosomes are believed to have originated by what?
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Invagination of the plasma membrane
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What 5 membranes are included in the Endomembrane system?
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1. Nuclear membrane
2. ER membrane 3. Golgi apparatus membrane 4. Endosome membrane 5. Lysosome membrane |
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Why do mitochondria and chloroplasts differ from all other organelles?
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they possess their own small genomes and can make their own proteins
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Mitochondria and chloroplasts might have evolved from what? Why?
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Bacteria because they have similar genomes and proteins
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The fate of any protein molecule synthesized in the cytosol depends on what?
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It's amino acid sequence which can contain a sorting signal that directs the protein to its organelle
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What happens to proteins that lack sorting signals?
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They remain in the cytosol FOREVER
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Proteins are imported into organelles by what 3 mechanisms?
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1. Through nuclear pores
2. Protein translocators 3. Transport vesicles |
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Proteins moving from the cytosol into the nucleus use what importing mechanism?
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Nuclear pores!
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Proteins moving from the cytosol into the ER, mitochondria or chloroplasts use what importing mechanism?
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Protein translocators!
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Proteins moving from the ER onward are transported with what mechanism?
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Transport vesicles!
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In order to go through a nuclear pore, does the protein have to be folded or unfolded?
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It can remain folded!
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In order to use protein translocaters, does the protein have to be folded or unfolded?
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It must be unfolded in order to snake through the membrane
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How long is a typical sorting sequence?
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15-60 amino acids long
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TRUE OR FALSE: the signal sequence is ALWAYS removed from the finished protein once it has been sorted.
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FALSE. It is not always removed.
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What physical properties often appear to be more important for the function of sorting signals than the exact amino acid sequence?
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Hydrophocity or the placement of charged amino acids!
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What is the Nuclear Lamina?
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A finely woven meshwork of protein filaments that line the inner face of the nuclear envelope.
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What is the purpose of the Nuclear Lamina?
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It provides the structural support for the nuclear envelope
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What might serve as a final quality-control step in mRNA synthesis and processing? Why?
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Nuclear transport through the pores because incompletely spliced mRNA will not be exported.
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How many proteins comprises a nuclear pore?
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30 different proteins
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What is the signal sequence that directs a protein from the cytosol into the nucleus called?
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Nuclear localization signal
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What is the Nuclear localization signal?
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Signal consisting of 1 or 2 short sequences containing several positively charged lysines or arginines
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What are Nuclear Transport Receptors?
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They are cytosolic proteins that bind to the nuclear localization signal on newly singthesized proteins destined for the nucleus.
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What are the 4 steps driving nuclear transport?
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1. Nuclear transport receptor binds cargo protein
2. Receptor transports cargo protein to nucleus 3. Cargo protein delivered to nucleus 4. Empty receptor returns to cytosol to repeat cycle again! |
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What is the third membrane system in chloroplasts called?
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Thylakoid membrane
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What help pull proteins across the two membranes of mitochondria and chloroplasts and help refold the protein once inside?
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Chaperone proteins!
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Proteins destined for the Golgi, endosomes, and lysosomes as well as proteins destined for the cell surface all enter what first?
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The ER from the cytosol
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What are the 2 kinds of proteins that are transferred from the cytosol to the ER?
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1. water-soluble proteins are translocated directly into the ER lumen
2. prospective transmembrane proteins are partly translocated across the ER and become embedded in it. |
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TRUE OR FALSE: Most of the proteins that enter the ER begin to be threaded across the ER membrane AFTER the polypeptide chain has been completely synthesized.
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FALSE. Sometimes they're threaded through DURING synthesis.
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The ER signal sequence is guided to the ER membrane with the aid of what 2 protein components?
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1. a signal-recognition particles (SRP)
2. SRP receptor |
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What signals determine the arrangement of a transmembrane protein in the lipid bilayer?
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Start and stop signals!
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What starts a major outward secretory pathway in transport vesicles?
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Starts with the synthesis of proteins on the ER membrane and their entry into the ER
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To function properly, what two things must transport vescicles do?
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1. Must only take with it the proteins needed in the destination
2. Must only fuse with the appropriate target membrane |
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Coated vesicles in vesicle transport serve what 2 functions?
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1. Shapes the membrane into a bud
2. helps to capture molecules for onward transport |
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The best studied vesicles are those with coats made up of what?
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The protein Clathrin.
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What is the purpose of Dynamin?
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It assembles a ring around the neck of each deeply invaginated coated pit of the vesicle which constricts and pinches off the vesicle.
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What is the purpose of Adaptins?
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This protein coat secures the clathrin coat to the vesicle membrane and helps select cargo molecules for transport.
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What are COP-coating vesicles involved in?
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They are involved in transporting molecules between the ER and the Golgi and from one part of the Golgi to another.
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What are Rab proteins?
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A family of small GTP-binding proteins present on the surfaces of transport vesicles and organelles that serve as molecular markers identifying each membrane type.
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What do Rab proteins ensure?
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Rab proteins help to ensure that transport vesicles fuse only with the correct membrane.
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Rab proteins are recognized by what?
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Tethering proteins on the cytosolic surface of the target membrane
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What are SNAREs?
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One of a family of membrane proteins responsible for the selective fusion of vesicles with a target membrane inside the cell.
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What do v-SNAREs do?
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They're the SNAREs on the vesicle that complement with t-SNAREs on the target membrane
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The size of the ER is controlled by what?
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The amount of protein that flows through it!
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What is Unfolded Protein Response?
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UPR is response triggered by the accumulation of misfolded proteins in the ER. The cell produces more ER and more of the molecular machinery needed to restore proper protein folding and processing.
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If proper balance cannot be reestablished and misfolded proteins continue to accumulate in the ER, what happens?
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The UPR program can direct the cell to self-destruct by undergoing apoptosis.
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Each Golgi stack has how many distinct faces? What are they called?
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1. Entry or cis face
2. Exit or trans face |
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Is Constitutive Secretion regulated or unregulated?
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Unregulated
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What are the two types of endocytosis?
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1. Pinocytosis
2. Phagocytosis |
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What is Pinocytosis?
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Ingestion of fluid and molecules via small vesicles
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What is Phagocytosis?
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Ingestion of large particles like microorganisms and cell debris
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What are large vesicles in phagocytosis called?
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Phagosomes
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In protazoa, phagocytosis is a form of what?
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Eating!
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What are pseudopods?
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Sheetlike projections from phagocytic cells that engulf bacterium after they bind to receptors on the phagocytic cell.
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Macrophages ingest how many worn-out redblood cells every day?
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10^11 cells!
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What is Receptor-Mediated Endocytosis?
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Mechanism of selective uptake of material by animal cells in which a macromolecule binds to a receptor in the plasma membrane and enters the cell in a clathrin-coated vesicle.
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Receptor-mediated endocytosis provides what mechanism to the cell?
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Provides concentrating mechanism that increases the efficiency of internalization of particular macromolecules more than 1000 fold compared to pinocytosis.
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How is Cholesterol transported in the blood?
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Bound to proteins in the form of low-density lipoproteins
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The interior of the endosome compartment is kept acidic or basic? How?
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It is kept ACIDIC by an ATP-driven H+ (proton) pump in the endosomal membrane.
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What are the 3 routes taken by receptors once they have entered an endosome?
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1. They return to the same plasma from whence they came!
2. They travel to lysosomes to be degraded 3. Proceed to a different domain of the plasma membrane (therefore transferring their bound cargo molecules across the cell) |
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What is Transcytosis?
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Transferring bound cargo molecules across the cell from one extracellular place to another
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What are the principle sites for intracellular digestion?
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Lysosomes!
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How many types of hydrolytic enzymes do lysosomes typically contain?
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40
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