Protein Trafficking Flashcards
Learning Objectives - Explain the mechanisms by which proteins are transported in the eukaryotic cell - Detail the difference between protein transport mechanisms within the context of specific organelles (gated, transmembrane, vesicular) - Highlight vesicular trafficking mechanisms via case study: the role of protein trafficking in osteoclasts
What is protein trafficking?
Process by which proteins are transported to desired locations within or across cells
How are proteins transporter within eukaryotic cells?
Vesicles
What is the lysosomal pathway?
Proteins are sent to the lysosome for degradation and/or recycling
List functions of lysosomes.
- DIGESTION
- Waste disposal
- Cell death (apoptosis)
List 4 types of lysosomes.
- Storage granules
- Digestive vacuoles
- Residual bodies
- Autophagic vacuoles
Explain the bidirectional traffic between the cytosol and nucleus.
Proteins that function in the nucleus are imported from the cytosol
- Histones
- DNA & RNA polymerases
- Gene regulatory proteins
- RNA processing proteins
tRNAs and mRNAs synthesized in the nucleus are exported to the cytosol
What are nuclear pore complexes (NPCs)
- Gates of the nucleus
- Restrict the movement of large molecules from crossing the nuclear envelope
- Direct the accumulation of selected macromolecules in either compartment (receptor-mediated, energy dependent, and fast transport)
What is the driving force that determines passive transport of solutes across a membrane
Electrochemical gradient or electrochemical potential different acting on the solute on both sides
What is active transport?
Movement of molecules across the membrane in combination with a carrier protein against the concentration gradient
Name the 2 simple diffusion pathways.
- Through the lipid bilayer
- Through the protein channels
What are the 2 types of active transport and what are they based on?
- Primary
- Secondary
- Based on source of energy
What drives primary active transport?
ATP breakdown
What drives secondary active transport?
Driven by ionic concentration differences created by primary active transport
Give an example of primary active transport.
- Sodium-potassium pump
- Complex of 2 globular proteins
- 3 Na+ receptors sites on inside
- 2 K+ receptor sites on outside
Give an example of secondary active transport.
- Glucose-Na+ symporter
- Brings an Na+ and glucose molecule into the cell
- Energy provided by concentration differences created by primary active transport
Describe the way vesicles travel through a cell.
- Spherical vesicles bud off and are carried along the cytoskeletal structures to another compartment
- Fuse with new compartment and let out the contents
What do osteoblasts do?
Form new bone tissue
What do osteoclasts do?
Break down and degrade old bone tissue
What are the 4 distinct membrane domains of osteoclasts?
- Sealing zone
- Ruffled border
- Basolateral domain
- Function secretory domain
What does osteoporosis do to bone density?
Lowers the density
What does the ruffled border do?
- Semi-permeable, lots of folds
- Allows small, non-polar molecules to passively diffuse
- Site where bone resorption happens
- Delivers proteins involved in the process (ex. V-ATPase to dissolve bone)
What does the sealing zone do?
- Attaches osteoclast to bone surface
- Isolates bone degradation area
What does the basolateral domain do?
- Ion exchange (Na+/K+ and Cl-/HCO3-)
- Maintains cellular homeostasis
- Includes the FSD and rest of cell membrane facing away from ruffled border
What does the functional secretory domain do?
- Exocytosis of bone degradation products after resorption
- Exit point for waste
