MCB7 - Intracellular Transport and Membrane Trafficking II Flashcards
Define glycosylation.
Attachment of carbohydrate group to functional group of other molecule. Mainly glycan groups attach to proteins via covalent bonds.
Which organelles are proteins modified in.
ER and Golgi apparatus
Where does initial glycosylation occur.
ER lumen
What happens to proteins translated by ribosomes on ER surface.
Fed into ER lumen. Folded into final structure. Glycosylation occurs alongside formation of disulphide bridges and assembly of multimeric protein. Protein becomes concentration and transport vesicle buds off and moves to Golgi.
What happens if a protein is misfolded in the ER lumen,
Exported out of ER by chaperone proteins. Degraded in cytosol.
What are chaperone proteins.
Proteins that bind to misfolded proteins helping to export them, allowing them to eventually be degraded.
What are the three areas of the Golgi apparatus.
Cis cisterna
Medical and trans cisterna
Trans Golgi network
Which side of the Golgi faces which side of the cell
Cis face faces the ER whereas trans face faces the cell periphery
What modifications occur in the Golgi and how are they carried out
Golgi enzymes carry out modifications such as further glycosylations. Addition of signal sequences which direct movement of protein into correct organelle.
Give example of enzyme involved in further glycosylation of proteins in Golgi apparatus.
Mannosidase enzymes
Discuss the cisternal maturation model.
Movement of proteins through Golgi which moves the cis cisterna to form the medial and trans cisterna and then eventually the trans Golgi network.
What are the three destinations of proteins from the Golgi apparatus.
Secretory vesicles.
Plasma membrane.
Lysosomes.
Define endocytosis.
Process by which cells take in material via invagination of plasma membrane
Define exocytosis.
Process by which material exits the cell via fusion of vesicle with plasma membrane
Where do endosomes release material from
Plasma membrane and Golgi
Discuss the outward secretory pathway
The transportation of newly synthesised material early then late endosomes and eventually to lysosomes.
Discuss inward secretory pathway.
Transportation of extracellular material into the cell where vesicles are pinched off from the plasma membrane.
Discuss the external medium and endocytosis.
Material transported is captured from external medium.
Discuss the external medium and exocytosis,
Material in vesicles formed inside the cell is the external medium
What is the name of compartments involved in vesicular budding.
Donor compartment - where vesicle buds from.
Target compartment - where vesicle fuses to.
How do transport vesicles move
Along cytoskeletal filaments e.g microtubules by the aid of motor proteins.
What is clathrin
Protein that forms the outside protein coat of a coated transport vesicle. Forms triskelions through leg domains to form the protein coat of a transport vesicle.
Where do transport vesicles bud from on the outward secretory pathway.
Trans Golgi network.
Where do transport vesicles bud from on the inward secretory pathway.
From the plasma membrane.
Define invagination
Formation of pit during vesicular budding.
What controls which substance will be in a transport vesicle.
Adaptin proteins mediate between clathrin and cargo receptors and so determine what proteins are to be transported in the vesicle,
What is the role of dynamin in vesicular budding.
Constricts the neck of the transport vesicle allowing it to bud off.
How do cargo proteins become detected by cargo receptors prior to vesicular budding
The cargo molecules contain signals which are recognised by cargo receptors.
After the vesicle has budded off, what happens to the protein coat.
Clathrin protein coat is shed and the clathrin and adaptin molecules are reused.
What are the four stages of vesicular transport.
Cargo sorting and vesicle formation
Vesicle movement
Vesicle tethering
Vesicle fusion
How do transport vesicles move within a cell.
Along microtubules which are cytoskeletal elements and are aided by motor proteins
If the plasma membrane is the acceptor compartment, what happens to the content within the transport vesicle.
Contents released into extracellular medium
What is a Rab protein.
Proteins that are specific to each transport vesicle that act as a marker for the vesicle. Grabbed by tethering proteins of target compartment to aid docking and vesicular fusion.
What are vSNAREs
Vesicular snare proteins that interact with tSNAREs to aid docking of vesicle prior to vesicular fusion.
What is a tethering protein.
Filamentous proteins on target compartment membrane that bind to Rab proteins to aid docking of vesicle.
What are the two types of exocytosis.
Unregulated (constitutive) and regulated
Difference between constitutive and regulated secretion.
Constitutive is unregulated so occurs continuously over time. Transport vesicle buds from Golgi apparatus containing protein to be transported. Fuses with acceptor compartment and is discharged. Acceptor compartment is plasma membrane, with cargo discharged into extracellular medium
Discuss process of regulated secretion as past of exocytosis
Occurs when specific signals are received e.g stimuli or voltage changes. Material forms transport vesicles. Signal transduction occurs causing contents to be released.
What are the three types of endocytosis
Pinocytosis.
Phagocytosis.
Receptor mediated endocytosis.
Discuss pinocytosis.
Ingestion of fluid and small molecules from extracellular fluid. Delivered to endosomes via pinocytosis.
How is fluid in a cell balanced by various cellular transport processes.
Fluid intake by endocytosis (pinocytosis) is balanced by fluid loss by exocytosis
Discuss process of phagocytosis as endocytosis.
Phagocytes engulf other cells or particles, commonly pathogens. Phagosome is formed bycell membrane which surrounds the particle to be engulfed.
What is the role of LDL receptors in receptor mediated endocytosis of cholesterol.
LDL receptors bind to LDL particles which surround cholesterol molecules to allow the endocytosis of cholesterol into a cell.
What is a LDL particle, it’s role and why it is needed.
Low density lipoproteins. Bind to cholesterol molecules. Allows uptake of cholesterol as LDL particles are insoluble. Ensures that small cholesterol particles are internalised without taking in too much extracellular fluid,
How are LDL receptors re used.
When entering the endosome, the LDL receptor is removed as the pH is too low in the endosome for the receptor to bind to the LDL particle. It is then returned to the plasma membrane via a vesicle.
Discuss process by which cholesterol can be endocytosed and incorporated into plasma membranes.
LDL particles form shell around cholesterol molecule. Bind to LDL receptor. Formation of clathrin coated vesicle, which fuses with the endosome. Receptor removed and LDL surrounded cholesterol is delivered to the lysosome. Hydrolysis enzymes within lysosome degrade LDL particles, releasing the cholesterol. Cholesterol is now free to be incorporated into the plasma membrane
How does cholesterol move from the lysosome to the cytosol after in has been internalised.
Binds to special transport proteins with hydrophobic regions which interact with cholesterol aiding its transport
