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72 Cards in this Set
- Front
- Back
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Trafficking
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The ways in which macromolecular components essential for cell function are delivered to their sites of function.
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3 Hereditary disesases of Trafficking:
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1. Cystic fibrosis
2. Familial hypercholesterolemia 3. Congenital sucrase isomaltase deficiency |
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Where is the trafficking abnormality in these hereditary disease?
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In going from the ER to the Golgi
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What surrounds the nucleus?
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A double membrane nuclear envelope.
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Where does transport occur across the nuclear envelope?
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Through pores.
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Site of synthesis of exportable protein and membrane proteins:
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Rough Endoplasmic reticulum
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Where is smooth ER particularly well-developed?
What is necessary for proteins to get into the ER? |
In liver cells and cells that make steroid hormones.
A Signal Recognition Particle |
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What makes up the Golgi complex?
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A system of smooth membranes and vesicles.
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What do the vesicles in the golgi complex contain?
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-Enzymes for processing exportable and membrane proteins
-Lysosomal enzymes. |
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What is the importance of the golgi complex?
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As a trafficking center.
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Lysosomes and endosomes are found where:
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throughout the cytoplasm.
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What do lysosomes contain?
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Acid hydrolases
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What are lysosomes important in?
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Macromolecular turnover.
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What is the function of endosomes?
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They are intermediate compartments involved in trafficking.
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What is the internal pH of both endosomes and lysosomes?
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Acidic
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What do we call the process of Synthesis of Protein for Export?
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The Regulated Secretory Pathway.
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What is a great model for Synthesis of Protein for Export?
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The pancreatic exocrine cell.
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How does the regulated secretory pathway progress?
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1. ER makes protein
2. Protein is processed through Golgi complex 3. Secretory vesicles form from the trans-golgi network 4. Proteins in vesicles leave cell via exocytosis |
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What are the pancreatic exocrine cells where this occurs?
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Acinus cells
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What pathway is responsible for continuous delivery of membrane components and ECM content?
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The unregulated constitutive secretory pathway.
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What makes the regulated and unregulated pathways different?
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The regulated pathway only secretes in response to a specific signal stimulus.
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Where does the process of protein trafficking begin?
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In RER
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Protein synthesized on ribosomes of RER is destined for:
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the lumen of the RER
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What 2 processes occur co-translationally in the RER?
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1. Translocation into the lumen
2. Insertion of membrane proteins |
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What is necessary for a protein to be translocated into the RER lumen?
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A signal sequence
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Where is the signal sequence for proteins destined for lumen import?
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At the amino terminal region of the nascent protein.
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What binds the signal sequence? Why?
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SRP - signal recognition particle; to stop translation.
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Why does translation need to stop?
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To allow the ribosome to associate with a ribosomal receptor on the RER membrane, and with an SRP receptor too.
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What happens once the ribosome binds its receptor and the SRP binds its receptor?
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Continued translation of the protein, but now into the lumen of RER.
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What happens to the signal sequence ultimately?
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It is extruded in the RER by a signal peptidase.
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What is needed for insertion of proteins into the membrane?
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Stop-transfer sequences.
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Where are most membrane lipid bilayers assembled?
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In the ER.
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What is the principal component of membrane lipid bilayers?
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Phosphatidylcholine (lecithin)
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Where is lecithin formed?
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In 3 enzymatic steps on the cytosolic surface of ER.
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Which side of the bilayer are lecthin molecules formed? How does a bilayer get made?
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-Formed on cytosolic side
-Flippase flips phosphatidylcholines to the other side to form the bilayer. |
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How is it decided whether proteins will stay and function in the golgi, or get exported?
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By the presence/absence of specific recognition signals for the ER.
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If proteins lack recognition signals for the ER what happens?
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They pass to the golgi complex by default.
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3 components of the Golgi:
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1. Cis cisternae
2. Medial cisternae 3. Trans cisternae |
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From which side of the Golgi do proteins enter?
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Cis
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What is the Trans cisternae referred to as? What happens here?
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trans-Golgi network - where vesicles for secretion pop off.
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What defines the sequential way in which the Golgi functions?
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The orderly assembly-line way that it trims and elongates N-linked oligosaccharides on proteins.
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What is the end result of core glycosylation?
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N-linked glycoproteins.
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When/where does Core glycosylation occur?
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In the ER, just after synthesis of the protein and lumenal translocation.
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What starts off core glycosylation?
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Transfer of a high-mannose core oligosaccharide from Dolichol phosphate.
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What does the oligosaccharide get transfered onto on a peptide?
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Asparagine
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What enzymes process the core oligosaccharide after transfer to Asn and make it more complex?
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-Glycosidases
-Glycosyl transferases |
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What do glycosidases do?
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Remove glucose and mannose from the core
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What do glycosyl transferases do?
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Add sugars to the oligosaccharide
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Where does the sequence of processing begin?
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In RER
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Where does the oligosaccharide-peptide go after processing begins in the ER?
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To the cis/medial Golgi
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What happens in the cis/medial golgi?
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-Additional mannose removed
-N-acetylglucosamine is added |
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What gets added in the trans Golgi?
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-Galactose
-Sialic acid |
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Functions of N-linked glycosylation:
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-Forming the Glycocalyx
-Calnexin-Calreticulin cycle |
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What is the glycocalyx?
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A polyanionic protein coat on the cell surface that can interact with molecular components of the ECM.
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Why is processing of the core oligosaccharide started by the RER important?
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Because it plays an important role in the proper folding of glycoproteins.
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What is the initial event in processing the core oligosaccharide? What is the resulting molecule?
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Removal of a terminal glucose by glucosidases I and II - forms a Monoglucosylated Oligosaccharide
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Why is it essential that the Monoglucosylated Oligosaccharide be formed?
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Becuase it permits binding of chaperones to ensure proper folding.
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What are the chaperone proteins?
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-Calnexin
-Calreticulin |
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What other protein aids in folding?
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ERp57
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What happens after ERP57 does its job?
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Glucosidase II removes the other glucosyl residue and results in the free Glycoprotein.
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What is ERGIC53?
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An RER membrane-bound protein that only binds glycoproteins if they're properly folded to allow them to leave the Golgi.
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What happens if the protein is NOT properly folded?
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It gets reglucosylated by Glucosyl transferase.
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How does Glucosyl transferase know to reglucosylate proteins?
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It recognizes improperly folded proteins.
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And we know what happens to monoglucosylated proteins:
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They bind Calnexin or Calreticulin and get folded.
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What is required for movement of macromolecules from RER to Golgi?
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Small coated vesicles
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What vesicles transport from RER to golgi?
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COPII vesicles
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What coats COPII vesicles?
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Coatamer proteins
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What vesicles move in the backwards direction in the Golgi stacks? (Trans -> cis)
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COPI vesicles
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2 Processes that Golgi vesicles are involved in:
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1. Transport between golgi stacks
2. Retrograde transport back to the RER |
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Why is retrograde transport from golgi to RER important?
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It returns resident proteins to the RER.
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What happens to the stacks of Golgi cisterns themselves?
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They also move from cis to trans direction.
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What is involved in the final steps of secretion from the trans-golgi network?
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-Prodution of secretory granules
-Their fusion with the plasma membrane |
