Flashcards in God is with me Deck (37):
What does Sar1 do?
1. A protein involved in membrane trafficking.
2. GTPase found in COPII vesicles.
3. Regulates assembly and disassembly of COPII coats.
Explain function of Sec12.
GDP-bound Sar1 interacts with membrane-bound exchange factor Sec12 and becomes Sar1-GTP.
2. Nterm of Sar1 then attaches to membrane and serves as binding site for Sec23/Sec24 protein coat complex.
What does Sec23 do?
Once the coat is complete and released with vesicle, it promotes Sar1 GTPase activity which triggers the disassembly of COPII coat.
What does calnexin do?
Retains unfolded or unassembled N-linked glycoproteins in the ER. (Is a chaperone)
What does COP I do?
Transports cargo from Golgi to ER within Golgi stacks (retrograde).
What does COP II do?
Transports cargo from ER to Golgi. (only assembled on cytosolic side, not ER)
What does clathrin do?
Transports cargo from Trans Golgi to Endosome; PM to Endosome.
Where do signal sequences belong?
What can KDEL do?
Retrieval of receptor protein that accidentally escapes ER.
Describe the steps of ERAD.
ER associated degradation:
1. Recognition of misfolded/mutated proteins in the ER.
2. Retro-translocation into the cytosol.
3. Ubiquitin-dependent degradation by proteasome.
What is the purpose of N-linked glycosylation?
1. Helps proteins fold correctly.
2. Protects from degrading quickly.
Which compartments are topologically equivalent to the extracellular space?
1. ER lumen
2. Interior of Golgi cisternae
3. Interior of lysosome
What does KDEL do?
An amino acid structure of a protein that keeps it from secreting/leaving the ER. Targets things back to the ER. Proteins can only leave ER after this sequence is cut off.
Type 1 membrane proteins have what in cytosol and what in lumen?
C terminus in cytosol. N terminus in lumen.
On what side does signal sequence recognition occur?
Cytosolic, not lumen.
Prion forming Prp adopts the _______.
Beta sheet confirmation.
Wild type non-prion forming is _____.
Transverse diffusion (flip-flop) is slow or rapid?
Lateral diffusion is slow or rapid?
What does fluorescent photobleaching recovery do?
Measures the rate at which diffusion takes place.
What is the difference and similarity of simple diffusion and facilitated diffusion?
Both: Higher to Lower concentration and no energy input.
Difference: Simple diffusion uses no transporters, while facilitated does (for large substances such as glucose).
How does the Na+/glucose co transporter work?
Na+/K+ pump creates conc. gradient for Na. Glucose transporter uses this energy/affinity to bring glucose into the cell against its concentration using the higher to lower conc gradient of the Na+.
What does myosin II do?
Dimer with two light chains for each heavy chain. Produces muscle contraction.
What does myosin V do?
Dimeric myosin with 36nm step size (total of 72nm length).
2. Walks towards barbed end (+)
3. May act as tether for vesicles and organelles.
What's unique about myosin VI?
Minus end directed motor along with IX.
What's unique about myosin VIII?
Plant-specific myosin involved in cell division.
Myosin II leads to what formation?
Thick filament formation.
What are the steps for when insulin is present (short version)?
1. Insulin -> IR -> IRS-1 -> P13K -> PDK1 -> PKB -> release of GLUT4 from cytoplasmic vesicle.
2. Glucose binds to GLUT4 and is transferred inside cell.
What are the steps for intrinsic apoptosis?
1. Internal cellular damage
2. Activation of proapoptotic BH3-only protein and subsequent activation of Bak or Bax
3. Bax channel/pore formed on surface of mitochondria
4. Release of cytochrome c through pore (electron transport and cell killer)
5. Apoptosome complex formed (Apaf-1 + cytochrome c + caspase 9) all recruited by cytochrome c.
6. Apoptosome cleaves executioner procaspases into caspase.
7. Apoptosis of targets.
What are the steps for insulin signaling? (long version)
1. Blood glucose increases
2. Insulin released
3. Insulin binds to alpha chain receptors and triggers trans-autophophorylation (RTKs) beta chain
4. IRS (Insulin receptor substrate) has PTB domain that binds to phosphate on RTK.
5. IRS acts as docking station for Grb2 -> SOS -> Ras-GTP and PI3K (2 subunits with SH2 domains)
6. PI3K phosphorylates 3' OH from PI(4,5)P2 into PIP3
7. PDK1 has PH domain that binds to PIP3
8. Bound PDK1 activates PKB.
9. Activated PKB induces protein synthesis, glucose uptake, and glycogen synthesis.
Explain the steps to the Epinephrine GPCR pathway.
1. Tyrosine binds to Epinephrine receptor.
2. Causes G-protein to bind to receptor.
3. GDP is exchanged for GTP.
4. G-alpha subunit with GTP now binds to effector protein.
5. Activated effector adenylyl cyclase makes cAMP (2nd messenger).
6. cAMP activates PKA (2 regulatory subunits and 2 catalytic subunits) by binding to 2 regulatory subunits causing catalytic subunits to dissociate.
7. Induces phosphorylation of enzymes (inhibits glycogen synthesis, and activates glycogen breakdown)
8. Also causes phosphorylation of transcription factors to increase glucose synthesis.
9. All of which increase [glucose]. (more glucose helps with stress response in brain/muscles)
What are the steps for the Serum response factor (SRF) and TCF pathway?
1. After ERK is phosphorylated and enters the nucleus, it induces phosphorylation of TCF.
2. Phosphorylated TCF binds to SRF and this complex increases expression of early response genes such as C-Fos and C-Jun.
3. Bound together Fos and Jun are phosphorylated and form AP-1 complex, which leads to increased expression of delayed response genes.
4. These delayed response genes are things like cyclins and CDKs, which are the engine for driving cell growth and division.
What are the steps for glucocorticoid signaling?
1. Steroid hormone (transcription factor) enters cytoplasm.
2. Binds to [receptor + Hsp90] chaperone complex causing Hsp90 to dissociate.
3. Receptor now has exposed NLS (nuclear localization signal) sending the signal/receptor into the nucleus.
4. Signal/Receptor complex dimerizes and attaches to a GRE sequence to regulate gene expression with the help of SWI/SNF BRG1 complex (DNA remodeling).
What are the basics about glucocorticoid signaling?
1. Stress hormone
2. Nonpolar = hydrophobic
3. Localized in cytosol
4. Can cross membrane freely
What are the steps for recognition of signal sequence on the ER?
1. Signal sequence on nascent polypeptide is recognized by SRP (signal recognition particle).
2. SRP attaches to signal and then binds to SRP receptor (arrests protein translation by blocking tRNA entry).
3. Upon binding, SRP dissociates from receptor following GTP hydrolysis.
4. Ribosome is now free to bind to Sec61 complex (translocon).
5. Peptide translocates into the ER lumen
What is the purpose of disulfide bonds in ER proteins and are they common?
Disulfide bonds stabilize proteins and promote folding and are common among ER proteins.
- PDI = protein disulfide isomerase