#ATP hydrolysis

Membrane Transportation

Which of the following ATP-powered pumps does not hydrolyze ATP during transport?

Pump classification by energy coupling highlights mechanistic differences. P-type ATPases such as Na+/K+ ATPase, SERCA, PMCA hydrolyze ATP phosphorylating conserved aspartate generating E1P E2P intermediates, actively transporting ions against gradients. V-type ATPases acidifying endosomes lysosomes vacuoles comprise Vo proton pore and V1 ATPase rotary motor hydrolyzing ATP to rotate c-ring driving proton translocation without phosphoprotein. ABC transporters dimerize nucleotide binding domains upon ATP binding to expel substrates. F-type ATPases known also as ATP synthases reside in mitochondrial inner membrane cristae, thylakoid membrane and bacterial plasma membrane. Crystallography shows Fo c-ring proton turbine and F1 head alpha3beta3. Under physiological respiring conditions proton motive force of 200 millivolts drives protons through Fo causing rotation of c-ring and central stalk gamma epsilon at about 100 hertz inducing binding change in catalytic beta subunits synthesizing ATP from ADP and phosphate via rotational catalysis, not consuming ATP for transport. Hydrolysis mode exists when gradient collapses pumping protons, but primary cellular operation synthesizes ATP using proton influx. Hence during principal physiological forward operation it does not hydrolyze ATP to drive ion transport, but manufactures ATP.

Ref: Nelson and Cox, Lehninger, F-Type ATPase Does Not Hydrolyze ATP During ATP Synthesis Mode.

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Membrane Transportation

Which subunit of Na+/K+ ATPase is responsible for ATP hydrolysis?

Na+/K+ ATPase catalytic function resides entirely in alpha subunit approximately 1000 amino acids organized into three cytoplasmic domains and ten transmembrane segments. N domain contains adenine binding pocket including Lys480, Arg544 interacting with ATP ribose and phosphates. P domain harbors DKTGTLT motif where Asp369 undergoes transient phosphorylation receiving gamma phosphate forming energy rich intermediate essential for conformational switching, and TGES motif in A actuator domain mediates dephosphorylation. Ion binding residues Glu327, Glu776, Asp804, Asp808, Thr797 line cavity in M4-M6, M8 coordinating sodium and potassium with alternating high low affinity. Mutations in alpha abolish phosphoenzyme formation and transport, ouabain binds in transmembrane vestibule locking E2P. Beta subunit single pass glycoprotein about 300 amino acids does not contain nucleotide binding or acid stable phosphorylation nor ion occlusion capacity. Its roles assembly, glycosylation trafficking via ER quality control, modulation of K+ affinity and cell adhesion signaling. Gamma FXYD small single span regulates kinetics tissue specifically. Therefore ATP hydrolysis responsibility assigned to alpha subunit catalyzing phosphorylation and energy coupling.

Ref: Kaplan, Biochemistry of Na+/K+ ATPase, Alpha Subunit Catalytic Domains and ATP Hydrolysis Site.

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Membrane Transportation

Which of the following uses primary active transport?

Primary active transport is defined by direct coupling of ATP hydrolysis within same protein to drive solute against gradient uphill requiring work. Sodium potassium ATPase exemplifies true primary pump prototype with ten transmembrane helices and three cytosolic domains forming P-type family characterized by transient phosphorylation of Asp369 during cycle. One ATP hydrolyzed phosphorylates P-domain inducing rearrangement from E1 to phosphorylated E2 state that translocates three sodium outward and two potassium inward per cycle consuming about quarter of ATP at rest generating electrogenic potential. In contrast GLUT1 and GLUT2 encoded by SLC2A are facilitative uniporters operating by alternating access rocker switch without ATP moving glucose down gradient passively saturable Km one to twenty millimolar stereoselective not energy linked expressed in erythrocytes brain liver beta cells for basal uptake. Aquaporins are tetrameric water channels each monomer forming pore allowing passive water diffusion at billion per second following osmotic gradient without energy gating by pH. Distinguishing categories crucial for pharmacology since ouabain digoxin specifically inhibit Na+/K+ ATPase binding extracellular side of E2-P while cytochalasin B inhibits GLUTs. Therefore primary active example among membrane proteins is sodium potassium ATPase requiring ATP directly.

Ref: Pirch et al., Annual Review of Physiology 2020: Primary Active Transport – Na+/K+ ATPase as P-type ATPase.

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Cytoskeleton

The power stroke of dynein is initiated by:

Unlike kinesin or myosin where ATP binding induces neck linker docking lever swing generating force dynein power stroke triggered specifically by ATP hydrolysis chemistry within AAA1 site coupling ring closure to linker movement distinct mechanism. Cycle stages: apo or ADP state linker straight spanning ring from tail to opposite side AAA4-5 high affinity microtubule binding strong attachment. ATP binding closes ring but microtubule already detached due to previous allosteric signaling via stalk. Hydrolysis of ATP to ADP Pi inside AAA1 produces large conformational change transmitted via AAA ring helical shifts to linker causing linker to bend from straight to pre power stroke curved configuration storing elastic strain and priming microtubule binding stalk forward position. Pi release closes stalk registry favoring high affinity binding and force generation as linker straightens power stroke dragging cargo toward minus end up to 32 nm power stroke size. ADP release resets motor cycle. Experiments using vanadate ADP Pi analogues trap pre power stroke state showing absolute requirement of hydrolysis rather than just binding to initiate force providing efficiency.

Ref: Carter et al., Science 2011 – Dynein power stroke initiated by hydrolysis of ATP in AAA1 domain mechanism.

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Cytoskeleton

How does kinesin-1 move along microtubules?

Kinesin-1 conventional motor transports cargo over long distances toward plus ends at velocities up to 1 micron per second. Heavy chain dimerization produces two motor heads coordinated via neck linker docking mechanism. Motility described as processive sliding or walking because motor maintains continuous association via at least one head bound at any moment preventing diffusion away from track essential for long range transport. ATP binding to leading head causes neck linker zipping toward plus end throwing lagging head forward to next binding site 8 nm ahead matching tubulin dimer repeat analogous to hand over hand stepping yet often simplified as sliding motion along filament surface maintaining electrostatic tethering via K loop. Interaction with microtubule via switch regions L8 L12. Tail associates with light chains binding cargo adaptors JIP Milton leading to activation by unfolding autoinhibition relieved only upon cargo binding preventing futile ATP consumption. This continuous attachment ensures efficient organelle movement without loss critical for axonal transport across meter long axons in larger mammals requiring high processivity.

Ref: Vale & Fletterick, Annu Rev Cell Dev Biol – Kinesin-1 sliding walking mechanism along microtubules processivity.

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Cytoskeleton

What happens when ATP is hydrolyzed by myosin in the actin-myosin cycle?

Actomyosin ATPase cycle illustrates chemomechanical coupling. Starting rigor actin myosin complex with empty nucleotide pocket tightly bound, ATP binding induces opening of actin binding cleft and dissociation rate 1000 per second. Free myosin closes Switch I Switch II around gamma phosphate hydrolyzing ATP to ADP inorganic phosphate with rate 50 per second, coupled to recovery stroke where lever arm swung 90 degrees from post stroke to pre stroke position, converter domain rotation storing elastic energy, myosin primed high energy configuration. This hydrolysis induced conformational change essential; without hydrolysis myosin would remain unprimed unable to generate force upon rebinding. Myosin ADP Pi then weakly attaches actin, strong binding and phosphate release drive power stroke, ADP release returns rigor. Actin filament does not depolymerize during cycle, actin stable scaffold, ADP release separate step after power stroke. Therefore ATP hydrolysis drives myosin head undergoing conformational change cocking lever arm into energized state preparing for phosphate gated power stroke that performs mechanical work during contraction.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 16: Myosin ATP Hydrolysis and Conformational Change.

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Bioenergetics

Which of the following is an example of an endergonic process?

Photosynthesis is the scientifically accurate answer to this question. Within the study of Bioenergetics, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of Photosynthesis directly address what is being asked. Among the other options, ATP hydrolysis, Cellular respiration, and Glycolysis do not correctly answer this question because they either refer to different concepts, describe properties of other molecules or processes, or represent common misconceptions about this topic.

Ref: Campbell Biology, Urry et al., 12th Ed.

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Bioenergetics

The free energy change of ATP hydrolysis in cells is approximately:

Both a and b is the scientifically accurate answer to this question. Within the study of Bioenergetics, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of Both a and b directly address what is being asked. Among the other options, -7.3 kcal/mol, -30 kJ/mol, and -50 kJ/mol do not correctly answer this question because they either refer to different concepts, describe properties of other molecules or processes, or represent common misconceptions about this topic.

Ref: Campbell Biology, Urry et al., 12th Ed.

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Bioenergetics

Which of the following statements about ATP hydrolysis is correct?

All of the above is the scientifically accurate answer to this question. Within the study of Bioenergetics, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of All of the above directly address what is being asked. Among the other options, Releases energy that is stored in phosphate bonds, Increases entropy in the system, and Is coupled to endergonic reactions do not correctly answer this question because they either refer to different concepts, describe properties of other molecules or processes, or represent common misconceptions about this topic.

Ref: Campbell Biology, Urry et al., 12th Ed.

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Bioenergetics

Which enzyme is responsible for ATP hydrolysis?

ATP synthase is the accurate response regarding enzymatic activity or regulation described in this question. Enzymes are biological catalysts that accelerate reactions by lowering activation energy through specific substrate binding and transition state stabilization. In the context of Bioenergetics, ATP synthase plays a specific catalytic or regulatory role determined by its active site configuration and mechanism of action. The other options (Kinase, Phosphatase, and Dehydrogenase) are either different enzymes with distinct substrate specificities, act through different mechanisms, or are involved in separate metabolic pathways.

Ref: Campbell Biology, Urry et al., 12th Ed.

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Protein

Which of the following chaperone families requires ATP hydrolysis?

All of the above is the scientifically accurate answer to this question. Within the study of Protein Folding, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of All of the above directly address what is being asked. Among the other options, Hsp60, Hsp70, and Hsp100 do not correctly answer this question because they either refer to different concepts, describe properties of other molecules or processes, or represent common misconceptions about this topic.

Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 4

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