Relationship between nucleus and ER
outer nucleus membrane is connected to membrane of ER
Smooth ER function
steroid hormone synthesis in endocrine cells
Golgi apparatus function
Receives proteins and lipids from ER, modifies them, and then dispatches (via vesicles) them to other destinations.
Endosome function
sorts ingested molecules + recycles some
lysosome function
degrades worn-out organelles, macromolecules and particles taken in by endocytosis
- contains hydrolytic enzymes (that can only function in acidic environments)
peroxisomes function
breaks down lipids + destroy toxic molecules
Properties of transport through nuclear pores
- proteins remain folded
- go through nuclear pores (selective to macromolecules, free diffusion to small micromolecules )
Properties of Transport across Membranes
- proteins usually unfolded
- transport via protein translocators
(proteins must unfold to bind to transolcators + pass through hydrophobic regions of membrane)
Properties of transport by vessicles
- involved in endo / exocytosis
- move via transport vessicle
- proteins remain folded
Signal sequences function
direct proteins to the correct destination
- 15 to 60 amino acids long
Nucelus properties
- double membrane
- connects to ER (for export from nucleuss)
- has nuclear pores (for import into nucleus)
Function of cystolic fibrils
weave in intricate formations to be selectively permeable to macromolecules
How do nuclear proteins get into the nucleus?
through the help of a nuclear import receptor that binds to proteins
What (and how does it) drives nuclear transport?
GTP hydrolysis
- Ran-GTP binds to receptor inside nucleus (allows receptor to exist nucleus)
- GTP is hydrolyzed, GDP dissociates from receptor (allows receptor to bind to proteins in the cytosol)
How do proteins enter mitochondria?
- protein binds to import receptors
- they unfold and pass through a protein translocator in outer membrane
- then, they pass through another protein translator in inner membrane
- signal sequence is cleaved off once inside matrix of mitochondria (mature protein forms)
Relationship between ribosomes and proteins
proteins bind to ribosomes to get synthesized.
Free ribosome cycle –> creates cytosolic proteins
membrane-bound ribosome cycle –> creates proteins that then enter the ER
How do ribosomes bind to ER membrane
proteins synthesized by ribosomes meant to enter the ER have an ER signal sequence
signal recognition particle (SRP) attaches to ribosome and binds to SRP receptor on cytosolic side of ER.
Where do stuff go in exocytosis?
- From Golgi Apparatus to plasma membrane
- From Golgi Apparatus to endosome to lysosome
Clathrin function
forms coated vesicles (protects from other proteins that might digest vesicles before it gets to where it goes )
What is glycosylation’s function?
- protects protein from degradtation
(asparagine is glycosylated ) - holds it in ER until protein is folded
- helps guide it to appropraite organelle
How does the cell deal with misfolded proteins
- retain in ER –> alters size of ER if there is many misfolded proteins
- unfolded protein response (UPR) –> activates chaperone proteins to refold proteins
- apoptosis (cell death) –> for a TON of misfolded proteins
2 pathways of exocytosis
- constitutive secretion (constant secretion)
- regulated secretion (requires extracellular signal in order to secrete) ex. neurotransmitters leave presynaptic membrane in nerve conduction when voltage gates for Ca2+ open and let Ca2+ to enter cell)
2 types of endocytosis
- pinocytosis (<150mm vesicles)
- phagcytosis (>250 mm vesicles)
–> uses pseudopods to engulf large stuff like other cells
How do virus enter the cell
- hack endocytic system (specifically by hijacking receptor-mediated endocytosis)
