unit 3 Flashcards
What is protein translocation?
Moving a protein a protein across a membrane.
What is cotranslational transport?
Transport in ribosome from cytoplasm to ER
What are three ways that proteins are sorted?
Gated transport, vesicular transport, protein translocation
What is the endomembrane system? What organelles makes it up?
Network of membranes related through physical contact or by transfer of vesicles. Made up of ER, golgi, endosomes, lysosomes
What path does vesicular transport take? What are the main steps?
ER –> golgi –> final location
1) vesicles bud off from donor membrane
2) moved via motor proteins on microtubules and microfilaments of cytoskeleton
3) fused with membrane of acceptor protein (destination organelle)
What are the two modes of secretion (and definitions)?
Constitutive: Materials transported in secretory vesicles continually
Regulated: Materials stored in vesicles and discharged in response to stimuli
How does the ER signal sequence direct ribosomes to ER membrane?
1) ER signal sequence on mRNA is translated and binds to srp on ribosome
2) ribosome travels to ER and srp binds to srp receptor (gtp hydrolysis)
3) translocon opens (facilitated by gtp hydrolysis)
4) translated protein send through protein translocator during translation
5) once translocon opened, translation resumes
What is a protein translocator (translocon)
A protein embedded in ER membrane that allows for co-translational transport of proteins. When srp and srp receptor bind to gtp and hydrolyse it, translocon opens and ribosome binds to it, allowing protein to ender rough ER
What is the srp
Comples thatr ecognizes ER signal sequence as it emerges from a ribosome and helps direct the ribosome to the ER by binding to the srp receptor on the ER and initiating th eopening of a protein translocator
Where is the ER signal sequence located?
N-terminus of mRNA strand?
What is the NPC
Nuclear pore complex. Proteins within the nuclear pore in the nuclear membrane that control which substances enter and leave the nucleus.
What is the nuclear basket?
Hold up structure of the NPC and regulate transport
What is the nuclear envelope?
A double membrane with nuclear pore complexes.
What are the steps of nuclear import?
1) Cargo protein has NLS (nuclear localization signals), which contain importin. NLS binds nuclear import receptors, which recognize the importin
2) Cargo-bound transport receptor binds to FG nups (nucleoporins)
3) Cargo released inside the nucleus when transport receptor bound by Ran-GTP
4) Transport receptor still bound to Ran-GTp diffuses through FG-nups to cytosol, where Ran GTP is released
Is NLS sufficient for transport of proteins into the nucleus?
Yes
Explain the Ran GTPase cycle?
Ran is bound to GDP in the cytosol. When it enters the nucleus, Ran GEF facilitates the unbinding of Ran to GDP and binding to GTP. (After the cargo protein has localized) Ran-GTP then diffuses back into the cytosol, where Ran-GAP hydrolyzes Ran-GTP, leading to Ran-GDP. The cycle can then restart.
What are the different types of molecules/proteins involved in cell signaling?
Extracellular signaling molecule –> receptor protein –> intracellular signaling molecules –> effector proteins
How does cell signaling work (basics)
Ligand binds to receptor, receptors on target cells receive extracellular message, effectors altered in response to ligand, second messenger or protein recruitment system lead to cellular response
What are the 4 forms of intercellular signaling
Contact-dependent, paracrine, synaptic (type of paracrine, just at a synapse) , endocrine
What is paracrine signaling?
The cell has receptors on its surface that respond to released messengers produces by other cells nearby
What is autocrine signaling?
The cell has receptors on surface that respond to released messengers produced from itself
What is endocrine signaling?
Messenger moelcules reach their target through the bloodstream
What are GCPRs and how do they work?
G coupled protein receptors. Signal molecule activates receptor and G protein, leading to activated enzyme
What are protein kinases?
Proteins that covalently add one or more phosphate groups to specific amino acids at hydroxyl groups
How do GTp binding proteins work?
They switch between two conformational states. GTP bound is “on” and GDP bound is “off”. Usually with GTPase activity to hydrolyze GTP
What are GTPase activating proteins (GAPS)?
They activate GTPases to increase the rate of hydrolysis of bound GTP. Results in turning GTP binding protein “off”
What are guanine nucleotide exchange factors (GEFs)?
They promote release of bound GDP in exchange for GTP, results in turning GTP-binding protein “on”
