Last Minute Midterm No. 3 Flashcards
Match the protein to its function in the actin system:
Profilin
Adenosine Exchange Factor (AEF)
Promotes growth at the + end, adds monomeric actin to the + end
Match the protein to its function in the actin system:
Thymosin
Sequesters actin-ATP monomers to create a reserve. Stockpiles actin-ATP monomers to hand off to profilin at appropriate times
Match the protein to its function in the actin system:
Arp2/3
Nucleates the formation of branches
The Arp2/3 complex is basically a regulated actin dimer. Its activator protein regulates filament nucleation/organization. Addition of 1 actin monomer (to activate the complex) yields a nucleating trimer
Arp2/3 complexes can also bind to the sides of pre-existing actin filaments (70 degree angle between filaments). This allows for networks of filaments fo form, branching
Match the protein to its function in the actin system:
Cofilin
“Promotes degradation” (re: breaks off chunks of filament) at the - end
Match the protein to its function in the actin system:
Formins
Nucleates the formation of linear filaments
Match the protein to its function in the actin system:
Rho
GTPase that regulates the formation of actin (different forms for linear vs branched)
Match the protein to its function in the actin system:
WASp
Scaffolding protein that facilitates the formation of branches
In muscle contractions, what happens when ATP binds to the myosin head?
Myosin releases the actin filament
In muscle contractions, what happens when ATP hydrolyzes?
The myosin head rotates and binds to actin?
In muscle contractions, what happens when Pi is released?
The power stroke
Which of the following receptors are most often implicated in cancer?
GPCRs
Notch
Ion channels
RTKs
Mechanoreceptors
Notch and RTKs
A wild type protein is destined for secretion outside the cell. Where would you find the majority of this protein if Sec23 was nonfunctional?
Rough ER lumen
A wild type protein is destined for secretion outside the cell. Where would you find the majority of this protein if Rab was nonfunctional?
In COPII vesicles
A wild type protein is destined for secretion outside the cell. Where would you find the majority of this protein if ARF was nonfunctional?
In the golgi lumen
A wild type protein is destined for secretion outside the cell. Where would you find the majority of this protein if v-SNAREs were nonfunctional?
In COPII vesicles
A wild type protein is destined for secretion outside the cell. Where would you find the majority of this protein if NSF was nonfunctional?
In COPII vesicles
A wild type protein is destined for secretion outside the cell. Where would you find the majority of this protein if Dynamin was nonfunctional?
On the trans-golgi face
A wild type protein is destined for secretion outside the cell. Where would you find the majority of this protein if Sar1 was nonfunctional?
In the rough ER lumen
GPCRs: active receptors act as a….
GEF
GPCRs: active effectors act as a….
GAP
How is Tau (a MAP) associated with Alzheimer’s?
When Tau is hyperphosphorylated, it dissociates from microtubules, aggregates, and forms neurofibrillary tangles, which contribute to Alzheimer’s.
Actin vs microtubules: polarity?
Both are polarized (only intermediate filaments aren’t polarized). They have + and - ends
Actin vs microtubules: general cellular location?
Actin: mostly at the cell surface
Microtubules: mostly at the cell interior near the nucleus and centrosomes
Actin vs microtubules: size?
Actin: smallest filament
Microtubules: largest filament
Actin vs microtubules: energy/NTP?
Actin: ATP
Microtubules: GTP
What kind of mutation in G(alpha) would leave it permanently activated?
Loss of function in it’s GTPase domain, so it would always remain in the GTP-bound ON state
Suppose the extracellular domain of the Notch receptor is covalently bound to the transmembrane domain. How would this affect the downstream effects?
Notch ligand can still bind, but the extracellular domain cannot be stretched to reveal cleavage site.
The extracellular domain is not endocytosed, so Notch stump is not exposed for further protease cleavage
Notch systolic fragment will not be released and cannot translocate to nucleus to change gene expression
Know your proteins!
Sar1
A GTPase that kicks of COPII vesicle formation, recruits Sec23/24 in its GTP bound state
Know your proteins!
Sec12
An ER bound GEF that activates Sar1
Know your proteins!
Sec 23
Directly binds to Sar1, recruits Sec24, a GAP that deactivates Sar1 after vesicle leaves ER
Know your proteins!
Sec24
Binds to Sec23, binds sorting signal of cargo protein
Know your proteins!
G(alpha)
(general)
GTPase, GTP bound form dissociates from G-protein to activate a single effector (adenylyl/guanylyl cyclase)
Know your proteins!
cAMP phosphodiesterase
Converts cAMP to AMP to turn off the message
Know your proteins!
PKA
Protein kinase A, stuck in an OFF state by regulatory subunits until cAMP removes those subunits, ON state can bind to cytosolic and/or nuclear targets to affect metabolism and gene transcription
Know your proteins!
GPCR kinase
Turns off GPCRs and inactivate them via endocytosis, signal desensitization
Works together with beta-arrestin
Know your proteins!
beta-arrestin
Turns off GPCRs and inactivate them via endocytosis, signal desensitization
Works together with GPCR kinase
What activates PKC?
Calcium release (rise in intracellular Ca2+ levels) and DAG binding
Know your proteins!
GRB2
Binds phosphorylated RTK, has SH2 and SH3 domains, recruits Sos
GRB2: SH2 domain
Binds to RTKs on phosphorylated tyrosine residues
GRB2: SH3 domain
Sos recruitment/binding domain
Know your proteins!
Sos
GEF that recruits+activates Ras
Know your proteins!
Ras
GTPase that kicks off phosphorylation cascade
Ras → Raf → MEK → MAPK
Cancer causing if left ON
Is alpha-tubulin always bound to GTP?
YES!!!
What does beta-tubulin do?
It’s a GTPase
When bound to GTP it can cap and stabilize a growing microtubule strand
Do heterodimers of alpha and beta tubulin spontaneously assemble into microtubule filaments?
NO!!!!
They need MTOCs to form their nucleation site!!!
Know your proteins!
Gamma-tubulin
Forms stable rings around nucleate microtubule and stabilizes/caps (–) end within pericentriolar material
Know your proteins!
MTOCs
Microtubule organizing centers, aka centrosomes
Pericentriolar material stabilizes the - end of microtubules
Know your proteins!
Kinesin13
Promotes increase of catastrophes, aka microtubule disassembly, promotes curling/peeling
Know your proteins!
MAPs
Microtubule associated proteins, decrease likelihood of disassembly, promote MT growth and stability, directs spacing between filaments
Know your proteins!
Tau
MAPs in the neuronal cells. When hyperphosphorylated, it dissociates from MTs and forms neurofibrillary tangles = Alzheimer’s
Know your proteins!
Katanin
Severs microtubules
Know your proteins!
Stathmin
Sequesters microtubule dimer pairs, prevents assembly
Formins FH2 domain
Acts as a molecular “rocking ratchet”
Promotes long, linear filaments
Acts in a dimer, binds to a actin dimers
Sits on the + end, stacks actin dimers appropriately
Formins RBD (Rho Binding Domain)
Small GTPase lipid-linked to the plasma membrane
Ensures polymerization happens near the plasma membrane, localizes polymerization
GTPase activity regulates the entire formin protein, regulates polymerization
Blocks unregulated function
FH2’s ratcheting+polymerization can occur only when Rho is bound to GTP (aka when Rho is active)
Formins FH1 domain
Recruits and binds to profilin-bound actin-ATP for FH2
Hands off the actin-ATP to be polymerized by FH2
Know your proteins!
CapZ
Caps actin thin filaments on the + end
Is myosin an ATPase?
YES!!!!!
Know your proteins!
Tropomodulin
Caps actin thin filaments on the - end
Know your proteins!
Thin filaments
Double capped actin filaments (CapZ on + end, tropomodulin on - end)
Know your proteins!
Thick filaments
Bipolar assemblies of myosin II molecules
Know your proteins!
Titin
Strong and large protein, works like a molecular spring. It holds the thin+thick filaments. Its spring action supports contraction and supports the myosin thick filaments
Titin has some unique folding structures that pop one at a time as it and its myosin thick filament stretches. It becomes unstructured as the muscle stretches, then becomes restructured when the muscle relaxes.
Know your proteins!
Nebulin
Wrapped around actin thin filaments
How are rises in intracellular Ca2+ levels related to skeletal muscle contraction?
Tropopmyosin’s wrapping position changes in response to Ca2+ levels
In a presence of high Ca2+, the increased Ca2+ levels cause tropomyosin to bind to troponin.
Troponin then pulls on the tropomyosin, which exposes the myosin binding sites
The pull/release of tropomyosin makes actin more and less accessible to the myosin heads
Ca2+ levels regulate access to myosin head binding sites. Contraction occurs only when Ca2+ levels are high
How are rises in intracellular Ca2+ levels related to smooth muscle contraction?
The myosin molecule itself is regulated by Ca2+ via calcium-calmodulin activation of myosin light-chain kinases
Myosin’s light chains will be differentially phosphorylated depending on whether myosin light chain kinase (mlck) has been activated by Ca2++calmodulin
Ca2+ binds to calmodulin, Ca2++calmodulin binds to and activates mlck, mlck phosphorylates myosin’s light chains
Phosphorylation of myosin’s light chains affects function it regulates whether myosin is extended (active) or folded (inactive)
Yes Pi → extended, functional, active
No pi → folded, nonfunctional, inactive
Myosin with ATP
Head NOT bound to actin filament
Myosin without ATP
Head IS bound to actin filament
Rigor mortis
In the absence of ATP (death), all myosin is bound to actin, stiffening the muscles
