Bioenergetics, Cellular Respiration, Photosynthesis, and Enzymes

Vocabulary practice flashcards covering photosynthesis, cellular respiration, oxidation-reduction principles, Gibbs free energy calculations, and enzyme inhibition mechanisms.

Light Reactions

The phase of photosynthesis taking place in the thylakoid membrane where light and $H_2O$ produce $O_2$, establish a high $[H^+]$ gradient, and generate $ATP$ (via ATP synthase) and $NADPH$.

Thylakoid

The membrane-bound compartment within the chloroplast where the light-dependent reactions occur and where a high $[H^+]$ proton gradient is established.

Stroma

The fluid-filled space of the chloroplast surrounding the thylakoids where the Calvin cycle takes place.

Carbon Fixation (Calvin Cycle Phase 1)

The initial step of the Calvin cycle in the stroma where inorganic $CO_2$ is incorporated into $RuBP$.

Reduction (Calvin Cycle Phase 2)

The second phase of the Calvin cycle in which fixed carbon is converted into $G3P$ using electrons from $6\,NADPH$ and energy from $6\,ATP$.

Regeneration (Calvin Cycle Phase 3)

The third phase of the Calvin cycle that consumes $3\,ATP$ to convert remaining $G3P$ molecules back into the $CO_2$ acceptor $RuBP$.

Glycolysis

A $10$-step pathway occurring in the cytosol that breaks down one $6C$ glucose into two $3C$ pyruvate molecules, yielding a net of $2\text{ pyruvate}$, $2\,NADH$, and $2\,ATP$ via substrate-level phosphorylation.

Pyruvate Oxidation

The mitochondrial step of cellular respiration per glucose molecule that converts $2\text{ pyruvate}$ into $2\text{ Acetyl CoA}$ ($2C$), releasing $2\,CO_2$ and producing $2\,NADH$.

Citric Acid Cycle

The cyclic pathway inside the mitochondrion that completes the breakdown of glucose derivatives, yielding $4\,CO_2$, $6\,NADH$, $2\,FADH_2$, and $2\,ATP$ via substrate-level phosphorylation per glucose.

Oxidative Phosphorylation

The production of ATP via the electron transport chain and chemiosmosis within the mitochondrion, utilizing electrons delivered by $NADH$ and $FADH_2$.

Substrate-Level Phosphorylation

The direct enzymatic formation of ATP from ADP and a substrate intermediate, contributing $2\,ATP$ in glycolysis and $2\,ATP$ in the citric acid cycle.

Oxidation

The loss of electrons from a substance during a chemical reaction ("Oxidation Is Loss").

Reduction

The gain of electrons by a substance during a chemical reaction ("Reduction Is Gain").

Redox Reaction

A paired chemical reaction involving the transfer of electrons, generalized as $Xe^- + Y \rightarrow X + Ye^-$, where $Xe^-$ is oxidized to $X$ and $Y$ is reduced to $Ye^-$.

$NADP^+$ / $NADPH$

The electron carrier pair utilized in photosynthesis; $NADP^+$ represents the oxidized state and $NADPH$ represents the reduced state.

$NAD^+$ / $NADH$

An electron carrier pair utilized in cellular respiration; $NAD^+$ represents the oxidized form and $NADH$ represents the reduced form.

$FAD$ / $FADH_2$

An electron carrier pair utilized in cellular respiration; $FAD$ represents the oxidized state and $FADH_2$ represents the reduced state.

$\Delta G$ (Gibbs Free Energy Change)

The difference between the free energy of products and reactants, calculated as $\Delta G = G_{\text{final}} - G_{\text{initial}}$ (or $P - R$).

Exergonic Reaction

A reaction characterized by the release of energy where $\Delta G$ is negative (for example, where products $P = 2$ and reactants $R = 12$, giving $\Delta G = 2 - 12 = -10$).

Competitive Inhibitor

An inhibitor molecule that directly binds to the active site of an enzyme, competing directly with the substrate for access.

Noncompetitive Inhibitor

An inhibitor that binds to a site that is NOT the active site, inducing a conformational change in the shape of the active site so the substrate cannot effectively bind.

Light Reactions

The phase of photosynthesis occurring in the thylakoid membrane where light energy drives the splitting of $H_2O$ into $O_2$, builds a proton ($H^+$) gradient across the thylakoid, and drives the synthesis of ATP via ATP synthase and the reduction of $NADP^+$ to $NADPH$.

Calvin Cycle

The light-independent stage of photosynthesis occurring in the stroma of the chloroplast, organized into three phases: carbon fixation, reduction, and regeneration.

Carbon Fixation

The first phase of the Calvin cycle where inorganic carbon ($CO_2$) is attached to the five-carbon acceptor molecule RuBP.

RuBP

Ribulose 1,5-bisphosphate; the carbon dioxide acceptor in the fixation phase of the Calvin cycle that is reconstituted during the regeneration phase using $3\text{ ATP}$.

Reduction (Calvin Cycle)

The second phase of the Calvin cycle in which fixed carbon intermediates receive electrons and phosphate groups from $6\text{ NADPH}$ and ATP to produce glyceraldehyde 3-phosphate ($G3P$).

Regeneration (Calvin Cycle)

The third phase of the Calvin cycle that utilizes $3\text{ ATP}$ to rearrange triose phosphate molecules back into RuBP so the cycle can continue.

Glycolysis

A $10$-step metabolic pathway located in the cytosol that splits one molecule of glucose ($6\text{C}$) into two molecules of pyruvate ($3\text{C}$), yielding a net of $2\text{ Pyruvate}$, $2\text{ NADH}$, and $2\text{ ATP}$ via substrate-level phosphorylation.

Pyruvate Oxidation

The transition stage of cellular respiration in the mitochondrion that converts two pyruvate molecules into $2\text{ Acetyl CoA}$ ($2\text{C}$), producing $2\text{ CO}_2$ and $2\text{ NADH}$ per glucose.

Citric Acid Cycle

The cyclical metabolic pathway in the mitochondrion that processes Acetyl CoA, producing $4\text{ CO}_2$, $6\text{ NADH}$, $2\text{ FADH}_2$, and $2\text{ ATP}$ via substrate-level phosphorylation per glucose.

Oxidative Phosphorylation

The final stage of cellular respiration consisting of the electron transport chain and chemiosmosis, which uses high-energy electrons from $NADH$ and $FADH_2$ to synthesize ATP.

Substrate-Level Phosphorylation

The direct enzymatic formation of ATP that occurs in glycolysis (yielding $2\text{ ATP}$ net) and the citric acid cycle (yielding $2\text{ ATP}$).

Oxidation

The chemical process defined by the loss of electrons ('Oxidation Is Loss').

Reduction

The chemical process defined by the gain of electrons ('Reduction Is Gain').

Redox Reaction

A coupled oxidation-reduction reaction where electron transfer occurs, represented by $Xe^- + Y \rightarrow X + Ye^-$, in which molecule $X$ is oxidized and molecule $Y$ is reduced.

$NADP^+$ and $NADPH$

The primary electron carrier pair in photosynthesis; $NADP^+$ is the oxidized form and $NADPH$ is the reduced form.

$NAD^+$ and $FAD$

The oxidized electron carriers utilized in cellular respiration that accept electrons to become the reduced electron carriers $NADH$ and $FADH_2$.

$$\Delta G$$

The change in Gibbs free energy, calculated as $\Delta G = G_{\text{final}} - G_{\text{initial}}$ (or $P - R$). When product energy is $2$ and reactant energy is $12$, $\Delta G = 2 - 12 = -10$.

Exergonic Reaction

A reaction characterized by a negative $\Delta G$ (such as $\Delta G = -10$), in which the initial free energy of reactants ($12$) is higher than that of products ($2$) and energy is released.

Competitive Inhibitor

An inhibitor that directly binds to the active site of an enzyme, competing with the substrate for access to the catalytic site.

Non-competitive Inhibitor

An inhibitor that binds to an enzyme at a site that is NOT the active site, inducing a conformational change that alters the shape of the active site.