Chapter 5 - Neural Science
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Synthesis and Transport of Neuronal Protein
Protein Synthesis in the Cell Body
- mostly in cell body and dendrite beginnings
- different sequences in N-terminal or inside mark it for different processes, for example, modification, secretion, or say degradation(Ubiquitinylation)
- chaperons(Hsp70) help in protein folding (energy dependent)
Protein Modification
- changes - cotranslational/ posttranslational
- permanent/transient
- N-acylation (Myristoylation) - addition of lipid chain to acylated N-terminus(Gly) allow it to associate with membrane through chain
- Thioacylation - allow protein to associate with cytosolic leaflet of membrane (e.g., helps GABA-secreting GAD to associate with membrane)
- Isoprenylation - also similar to thioacylation, by farnesyl, or geranyl-geranyl
- Reversible - (de)phosphorylation, which also controls enzyme kinetics
- ATP-ubiquitin-proteasome pathway - selective and regulated proteolysis of cytosolic proteins, important in many neuronal processes, including synaptogenesis and long-term memory storage
Cytosolic protein uptake by other organelles
- Nuclear import of large proteins through pores - requires energy, marked with nuclear localisation signals and export signals for opposite
- Mitochondrial and peroxisomal transport- signal sequence is amphipathic helix so that it can cross bilayer
Protein synthesis and modification in ER
- Signal recognition particle & stop-transfer sequences mediating transport during cotranslation
- glycosylation
- intramolecular disulfide linkages
Modification and processing by Golgi bodies
- clathrin-coated vesicles
- mechanism of transfer
Endocytosis
- reuse of used synaptic vesicles
- very selective transport by clathrin mediated vesicles, termed receptor mediated endocytosis
Axonal transport
- used by scientists to visualise neurons and neuronal networks
- labelled material carried by the axon helps visualise the entire network
- e.g., Herpes Simplex virus has been used to trace cortical pathways in monkeys
- Anteretrogade - towards axon terminal, Retrograde - towards terminal ^7b597c
- Moderate slow movement of axoplasm from cell body to terminal over time (axoplasmic transport) visualised by Paul Weiss in the sciatic nerve
- membranous proteins - both anteretrograde & retrograde (fast axonal transport)||| cytoplasmic skeletons and proteins - only retrograde (slow axonal transport)
- used by scientists to visualise axonal transport and neural network