TA tutorials Flashcards
How does the ∆G influence the rate of a reaction?
The ∆G does not influence the rate of a reaction. The reaction is inversely proportional to the activation energy
(ΔG‡)ΔG = G Products − G Reactants
How is the energy from one reaction transferred to another reaction ?
1: Transfer of a phosphate group (Ex: ATP
2: In many chemical reactions, electrons are transferred
Release of energy can be coupled to other reactions
What would be the probability of breaking a bond that has an Energy of 5 KbT
P= 0.0067 (e^-5)
What do microtubules do?
Long-range transport
Mitotic spindle
Backbone of neurons
Structure of cilia
A mutation prevents a Rho GAP from interacting with Rho-GTP. Predict how this would affect the actin cytoskeleton and cell behavior.
Rho-GTP (active Rho) could not be turned off, and would continue signalling to effector proteins, thus significantly increasing the production of actin stress fibers
How does Rho activate formins?
A.By phosphorylating forminsat their FH2 domain
B.By binding to the Rho-binding domain and relieving auto-inhibition
C.By binding directly to the FH1 domains
D.By recruiting actin monomers to the formins
B
You are trying to develop a drug which can disrupt microtubule growth. What could it do to achieve this?
A.Sequester free tubulin dimers
B.Block GTP hydrolysis
C.Inhibit a destabilizing microtubule-associated protein
D.Ensure the stability of kinesin-13
E.All of the above
ABD
Which of the following are true of actin but not of microtubules?
A.Growth occurs at the (+) end of the polymer
B.Nucleation occurs through proteins which provide a template for the growing polymer
C.They are integral parts of the cell’s cytoskeleton
D.Rate constants defining the dynamics of monomer addition and removal are well defined
D
Why is the second law of thermodynamics critical in understanding cellular energy use?
a) It explains energy conservation in isolated systems.
b) It dictates that cells can convert heat into work.
c) It describes how cells maintain order despite increasing entropy.
d) It explains why ATP hydrolysis releases energy.
C
The second law states that entropy in an isolated system increases. Cells combat this by utilizing free energy (e.g., from ATP hydrolysis) to maintain order and drive processes.
Why do cells utilize both NAD+ and FAD as electron carriers?
a) NAD+ is used for anabolic reactions, while FAD is used for catabolic reactions.
b) FAD accepts electrons when NAD+ is unavailable.
c) NAD+ is reduced in high-energy reactions, while FAD is used for reactions with smaller energy changes.
d) FAD is used exclusively in photosynthesis.
c
NAD+ is reduced in reactions with significant free energy changes, while FAD is reduced in reactions where the energy released is insufficient to reduce NAD+.
What is the role of GAPDH in cellular metabolism?
a) Converts ATP to ADP during glycolysis.
b) Reduces NAD+ to NADH by positioning it during glycolysis.
c) Acts as a proton pump in the electron transport chain.
d) Hydrolyzes glucose to release energy directly.
b
Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) reduces NAD+ to NADH during glycolysis by facilitating the transfer of electrons from glyceraldehyde-3-phosphate.
What is the significance of a low Reynold’s number in cellular environments?
a) Diffusion dominates over inertial effects.
b) Viscosity becomes negligible.
c) Cells can freely move through cytoplasmic meshwork.
d) Elasticity decreases, making cytoplasmic motion random.
a
In low Reynold’s number environments, like the cytoplasm, viscous forces dominate over inertial forces, making diffusion the primary means of molecular motion.
Why is the 70° angle created by Arp2/3 nucleation optimal for cell motility?
A. It allows rapid detachment of actin filaments during movement.
B. It creates a dense network that efficiently pushes the plasma membrane forward.
C. It stabilizes stress fibers to maintain cellular tension.
D. It prevents Profilin from recycling actin monomers.
b
The 70° angle generated by Arp2/3 nucleation ensures that the resulting branched actin network is dense and properly oriented to exert force on the plasma membrane, facilitating forward movement of the cell
How does Thymosin-β4 contribute to actin regulation?
A. It binds to actin filaments to sever them.
B. It nucleates actin filaments at a 70° angle.
C. It sequesters actin monomers, keeping them in reserve.
D. It cross-links actin filaments into bundles.
c
Thymosin-β4 binds to actin monomers and prevents them from polymerizing. This creates a reserve of actin monomers that can be readily released when needed for dynamic filament assembly during cellular processes like motility
In the absence of Formins, how would actin filament polymerization be affected?
A. The filaments would fail to nucleate.
B. Linear filament growth would be significantly reduced.
C. Branched filament networks would collapse.
D. Actin filaments would polymerize uncontrollably.
b
Formins facilitate the polymerization of linear actin filaments by remaining attached to the filament’s plus end, enabling the addition of actin monomers. Without Formins, linear filament growth is impaired, affecting structures like stress fibers
How does WASp activate the Arp2/3 complex?
A. By binding ATP and transferring it to Arp2/3.
B. By mimicking an actin nucleus and inducing actin polymerization.
C. By stabilizing the interaction between actin filaments and Arp2/3.
D. By binding to actin monomers and inducing a conformational change in Arp2/3.
d
WASp contains a WH2 domain that binds actin monomers and an acidic domain that induces conformational changes in the Arp2/3 complex, enabling it to nucleate branched actin filaments
What would be the impact of a mutation that prevents Cofilin from severing actin filaments?
A. Actin filaments would become shorter and less dynamic.
B. Actin networks would lack branching, leading to impaired motility.
C. Treadmilling would slow down, reducing actin filament turnover.
D. Actin monomers would polymerize uncontrollably at the plus end.
c
Cofilin’s severing activity increases the number of filament ends available for polymerization and depolymerization, accelerating treadmilling. Without Cofilin, actin filament turnover would slow, impairing cellular motility
A cell is engineered to express a mutant version of Cofilin that cannot bind actin filaments. What would be the most likely consequence?
A) Actin filaments would become excessively branched
B) Actin polymerization at the leading edge would increase
C) Actin treadmilling would slow down significantly
D) Myosin-II activity would increase in stress fibers
c
Cofilin severs actin filaments and enhances depolymerization at the pointed (-) end, replenishing actin monomers for new filament growth. Without Cofilin, actin filaments would turn over more slowly, leading to inefficient cytoskeletal remodeling.
A researcher is studying a new protein that binds to actin filaments and increases the rate of depolymerization at the pointed (-) end. Which of the following proteins does this new protein most closely resemble?
A) Formin
B) Thymosin-β4
C) Cofilin
D) CapZ
c
CofilinbindsADP-actinfilamentsandpromotesdepolymerizationat thepointed(-) end, enhancingactinfilamentturnover.Forminpromotespolymerization,Thymosin-β4sequestersactinmonomers,and CapZpreventspolymerizationat thebarbed(+) end
Which of the following best describes the role of Dynamic Instability in microtubules?
A) It ensures that microtubules constantly grow without shrinking
B) It allows microtubules to rapidly reorganize in response to cellular needs
C) It stabilizes microtubules by enhancing GTP hydrolysis
D) It prevents microtubules from depolymerizing by capping their ends
b
Dynamic Instability refers to the rapid switching between growth and shrinkage, enabling microtubules to explore intracellular space and quickly respond to changes in cell shape or division.
A newly discovered toxin prevents dynein from interacting with microtubules. Which cellular function would be most directly affected?
A) Anterograde transport of vesicles
B) Retrograde transport of organelles toward the nucleus
C) Microtubule polymerization at the centrosome
D) Chromosome condensation during mitosis
b
Dynein is a minus-end-directed motor protein that carries organelles and vesicles toward the centrosome (retrograde transport). Inhibiting dynein would disrupt intracellular trafficking.
A researcher isolates a new microtubule-associated protein (MAP) that promotes microtubule growth and prevents catastrophe. Which known protein does this resemble?
A) Kinesin
B) Tau
C) EB1
D) Dynein
c
EB1 is a +TIP protein that stabilizes growing microtubules and prevents catastrophe. Tau stabilizes axonal microtubules, but EB1 is more directly involved in growth.
A scientist isolates a neuronal mutant in which axonal microtubules are highly unstable. Which of the following proteins is most likely defective?
A) Dynein
B) Tau
C) EB1
D) Kinesin
b
Tau stabilizes microtubules in neurons.Without it, microtubules become unstable, leading to axonal dysfunction.
Which motor protein transports neurotransmitters from the soma to the pre-synapse?
kinesin
Select the processes that are possible without microtubules:
1) Motility
2) Short range vesicle transport
3) Mitosis
4) Myosin-based transport
5) Long-range vesicle transport
1,2,4
Which of these proteins promote microtubule disassembly?
1) Tau
2) EB1
3) XMAP215
4) Katanin
5) Kinesin-13
2,4,5
2) EB1 : This protein enhances GTP hydrolysis in the cap and increases the rate of catastrophes.
4) Katanin : Katanin promotes microtubule severing. This can increase the number of free ends for depolymerization
5) Kinesin-13 : This protein promotes disassembly. It binds and curves the end of tubulin protofilaments as well as removes terminal tubulin dimers. This enhances catastrophes.Practice questions
Which protein family is primarily responsible for recognizing the GTP-cap of microtubules and promoting stability at the plus-end?
A) XMAP215
B) EB proteins
C) Dyneins
D) Katanin
b
EB proteins (end-binding proteins) specifically recognize and bind to the GTP-cap of microtubules, promoting stability and serving as a platform for other +TIP proteins. XMAP215 accelerates growth, while dyneins are motor proteins and katanin severs microtubules.
Which of the following proteins would you expect to prevent microtubule catastrophe and promote microtubule growth?
A) Katanin
B) MCAK
C) XMAP215
D) Dynein
c
XMAP215 acts as a microtubule polymerase, accelerating microtubule growth and stabilizing tubulin dimers at the plus-end, preventing catastrophe.
A mutation that enhances MCAK activity would most likely result in:
A) Stabilization of microtubules
B) Increased microtubule polymerization
C) More frequent microtubule catastrophes
D) Reduced nucleation at the centrosome
c
MCAK is a depolymerase that removes tubulin from the ends of microtubules, triggering catastrophe. Increased MCAK activity would lead to frequent depolymerization events.
Kinesin takes multiple steps along a microtubule without dissociating. This property is known as:
A) Processivity
B) Catalysis
C) Allosteric regulation
D) Power stroke
a
Processivity refers to the ability of kinesin to take consecutive steps along a microtubule without detaching. This is crucial for efficient cargo transport over long distances
Phosphofructokinase-1 (PFK1) is inhibited by which of the following molecules under normal cellular conditions?
A) AMP
B) Citrate
C) Fructose-6-phosphate
D) NADH
b
Citrate acts as an allosteric inhibitor of PFK1, signaling that the cell has sufficient biosynthetic intermediates. AMP activates PFK1, while NADH and fructose-6-phosphate do not directly inhibit it.
Which of the following best describes the role of the mitochondrial permeability transition pore (mPTP) in apoptosis?
a) The mPTP helps in mitochondrial fusion to enhance ATP production.
b) The mPTP opens in response to mitochondrial stress, causing loss of membrane potential and promoting the release of apoptotic factors like cytochrome c.
c) The mPTP is involved in the process of mitochondrial fission, enabling equal segregation during cell division.
d) The mPTP prevents the release of reactive oxygen species (ROS) from the mitochondria during metabolic stress.
b
The mitochondrial permeability transition pore (mPTP) is involved in the disruption of mitochondrial membrane integrity under stress conditions. When the mPTP opens, it leads to mitochondrial depolarization, loss of ATP, and the release of pro-apoptotic factors, such as cytochrome c, which triggers apoptosis. Option a is incorrect as the mPTP is not directly related to mitochondrial fusion. Option c is incorrect because mPTP is related to membrane permeability, not fission. Option d is incorrect as the mPTP release of factors contributes to apoptosis, not ROS inhibition.
