Cellular Respiration, Photosynthesis, and Metabolic Pathways

Vocabulary flashcards covering cellular respiration, photosynthesis, organelle locations, key enzymes, thermodynamic pathways, and feedback mechanisms.

Cellular Respiration

The metabolic process with the formula $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy(ATP + heat)}$, which yields approximately $30\text{-}32\text{ ATP}$ per glucose molecule.

Photosynthesis

The metabolic process with the formula $6CO_2 + 6H_2O + \text{LightEnergy} \rightarrow C_6H_{12}O_6 + 6O_2$, which is the exact chemical opposite of cellular respiration.

Glycolysis

The initial step of cellular respiration in the cytoplasm where a 6-carbon glucose is split into two 3-carbon pyruvates, yielding $4\text{ Gross ATP}$, $2\text{ Net ATP}$, and $2\text{ NADH}$.

Pyruvate Oxidation (Link Reaction)

The stage where pyruvate enters the mitochondrion, loses a carbon as $CO_2$, forms Acetyl-CoA, and yields NADH with $0\text{ ATP}$ produced.

Krebs Cycle (Citric Acid Cycle)

The stage in the mitochondrial matrix where Acetyl-CoA is completely oxidized, carbons leave as $CO_2$, and a payload of $6\text{ NADH}$, $2\text{ FADH}_2$, and $2\text{ Net ATP}$ ($1\text{ per turn}$, $2\text{ turns per glucose}$) is generated.

Oxidative Phosphorylation

The process consisting of the electron transport chain and chemiosmosis where NADH and $FADH_2$ donate electrons to create an $H^+$ gradient that powers ATP Synthase to generate approximately $26\text{-}28\text{ Net ATP}$.

Mitochondrial Matrix

The internal compartment of the mitochondrion where pyruvate oxidation and the Krebs Cycle occur.

Inner Mitochondrial Membrane (Cristae)

The inner membrane structures of the mitochondria where the Electron Transport Chain is embedded.

Thylakoid Membranes

Chloroplast membranes where light strikes Photosystems II and I and the light-dependent reactions of photosynthesis take place.

Stroma

The fluid inside the chloroplast where the light-independent Calvin Cycle occurs.

Rubisco

The most abundant enzyme on Earth; it fixes $CO_2$ to a 5-carbon molecule (RuBP) to initiate the Calvin Cycle.

NADP+ Reductase

An enzyme that transfers electrons to NADP+ to form NADPH at the conclusion of the light reactions of photosynthesis.

Phosphofructokinase (PFK)

The pacemaker of glycolysis; an allosteric enzyme regulated by ATP via negative feedback.

Dehydrogenases

Enzymes that remove hydrogen and electrons from molecules to transfer them to NAD+ and FAD.

ATP Synthase

A shared molecular mill powered by the flow of $H^+$ ions through chemiosmosis to synthesize ATP.

Calvin Cycle

The light-independent process in the stroma where Rubisco fixes $CO_2$ to RuBP, reducing carbon molecules into G3P using ATP and NADPH, before regenerating RuBP.

G3P

A 3-carbon sugar produced in the Calvin Cycle through the reduction of carbon molecules that subsequently becomes glucose.

Exergonic Reaction

A spontaneous reaction that releases energy and is characterized by $-\Delta G$, such as cellular respiration.

Endergonic Reaction

A non-spontaneous reaction that requires energy input and is characterized by $+\Delta G$, such as photosynthesis.

Catabolic Pathways

Metabolic pathways that break down complex molecules into simpler ones, releasing energy (e.g., hydrolysis, cellular respiration).

Anabolic Pathways

Metabolic pathways that build complex molecules from simpler ones, consuming energy (e.g., dehydration synthesis, protein synthesis, photosynthesis).

Negative Feedback

A pathway regulation mechanism where the end product inhibits an earlier step to stop the process, maintain homeostasis, and prevent wasting resources (e.g., ATP binding to PFK).

Positive Feedback

A regulatory mechanism where a product or response amplifies the original signal, pushing the process further away from homeostasis to complete a specific task (e.g., fruit ripening via ethylene gas, oxytocin release during childbirth).