AP Biology :3.4 Cellular Energy – Exam Style questions with Answer- FRQ

Question

State and describe the energy transformations involved in the chemiosmotic production of ATP.

▶️Answer/Explanation

Ans:

Chemiosmosis is the mechanism by which a hydrogen ion gradient
is used to drive an energy-requiring process, like the synthesis of ATP.
In mitochondria and chloroplasts, ATP synthase performs this function.
Building a gradient requires energy. If the ultimate goal of chemiosmosis
is the synthesis of ATP, the use of ATP to build the proton would, at best,
result in no net ATP (and in reality, no energy transformations in the cell are
100% efficient, so you’re going to use more energy than you harness). The
energy to drive the proton pumps is harnessed from the electrons delivered
to the electron transport chain by NADH or \(FADH_2\) in the mitochondria and by an electron acceptor in photosystem II in the chloroplast.
In the mitochondria, the movement of electrons from NADH and
\(FADH_2\) to oxygen, creating water, has a (very) negative free energy
change; that is, it is exergonic, spontaneous, and downhill. The potential
energy of the electrons is lowered, which means there was a conversion of
potential energy to other forms of energy. The change in potential energy,
from lower stability glucose to higher stability water, is what drives the
protons against their concentration gradient. This is a coupled process. A
downhill process can drive an uphill process if they are coupled. Every endergonic process has a price. See answer 124 for an explanation of how a proton gradient stores potential energy. The potential energy of the gradient is raised with each proton that enters the high concentration compartment and lowered with each proton that leaves. The spontaneous flow of hydrogen ions from high to low concentration drives the endergonic synthesis of ATP. The exergonic processes are the downhill, driving reactions. They spontaneously happen. The endergonic processes require work. The energy to do the work is harnessed from the reaction it is coupled with. Coupled processes occur concurrently in the same place. They are physically
and temporally linked. The first two reactions occur at the cytochrome complexes. The oxidation-reduction reactions of the transport of the electrons down the chain provide the energy for proton translocation. The cytochrome complexes are multi-protein complexes composed of electron carriers and a proton pump. The second two processes are coupled through ATP synthase. The giant, multi subunit protein complex also translocates protons, but in the direction of their diffusion, harnessing the energy of their diffusion for the synthesis of ATP from ADP and \(P_i\).

Question.

Eukaryotes depend on energy stored in biological molecules.
(a) Compare and contrast how ATP is produced in the following two pathways.
• Oxidative phosphorylation in mitochondria
• Photophosphorylation in chloroplasts
(b) For THREE of the following, describe the specific role of ATP.
• Muscle contraction in animals
• Transport of water into root hairs
• Movement of chromosomes during anaphase
• DNA replication

▶️Answer/Explanation

(a)

(b)

• Muscle contraction in animals
− ATP binds to myosin head, converts to ADP + P, and myosin is phosphorylated (energized).
−\( Ca^{++}\) exposes the binding sites for actin filaments;\( Ca^{++}\) binds to troponin causing tropomyosin to expose positions on the actin filament for attachment of myosin heads.
− Cross bridges between actin and myosin form.
− ADP + P are released, and the sliding motion occurs (change in shape between actin and myosin, which generates a sliding movement and, when amplified many times, results in the pulling of many myofibrils together.
• Transport of water into root hairs
− Ions are actively transported from the soil into cells by protein carriers.
− ATP phosphorylates the proteins, changing their confirmation and powering the ion transport.
− The transported ions create a concentration gradient (water potential).
− Water passively diffuses into the cell down the concentration gradient.
• Movement of chromosomes during anaphase
− During anaphase, kinetochore microtubules shorten to “walk” toward respective poles.
− Using energy from ATP, motor proteins reduce tubulin into subunits.
− As microtubules move apart, the spindle poles move apart, elongating the cell.
• DNA replication
ATP “hydrolysis” is needed for the following processes:
− Formation of other deoxynucleotide phosphates: GTP, CTP, and TTP.
− Elongation of the growing strand (can be powered by ATP or other deoxynucleotide triphosphate).
− Ligation (can be powered by ATP or other deoxynucleotide triphosphate).
− Movement of the DNA polymerase complex.
− Unwinding the helix.

Question.

Eukaryotes depend on energy stored in biological molecules.
(a) Compare and contrast how ATP is produced in the following two pathways.
• Oxidative phosphorylation in mitochondria
• Photophosphorylation in chloroplasts
(b) For THREE of the following, describe the specific role of ATP.
• Muscle contraction in animals
• Transport of water into root hairs
• Movement of chromosomes during anaphase
• DNA replication

▶️Answer/Explanation

(a)

(b)

• Muscle contraction in animals
− ATP binds to myosin head, converts to ADP + P, and myosin is phosphorylated (energized).
−\( Ca^{++}\) exposes the binding sites for actin filaments;\( Ca^{++}\) binds to troponin causing tropomyosin to expose positions on the actin filament for attachment of myosin heads.
− Cross bridges between actin and myosin form.
− ADP + P are released, and the sliding motion occurs (change in shape between actin and myosin, which generates a sliding movement and, when amplified many times, results in the pulling of many myofibrils together.
• Transport of water into root hairs
− Ions are actively transported from the soil into cells by protein carriers.
− ATP phosphorylates the proteins, changing their confirmation and powering the ion transport.
− The transported ions create a concentration gradient (water potential).
− Water passively diffuses into the cell down the concentration gradient.
• Movement of chromosomes during anaphase
− During anaphase, kinetochore microtubules shorten to “walk” toward respective poles.
− Using energy from ATP, motor proteins reduce tubulin into subunits.
− As microtubules move apart, the spindle poles move apart, elongating the cell.
• DNA replication
ATP “hydrolysis” is needed for the following processes:
− Formation of other deoxynucleotide phosphates: GTP, CTP, and TTP.
− Elongation of the growing strand (can be powered by ATP or other deoxynucleotide triphosphate).
− Ligation (can be powered by ATP or other deoxynucleotide triphosphate).
− Movement of the DNA polymerase complex.
− Unwinding the helix.

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