Lecture 9: Glycolysis, Citric Acid Cycle & Oxidative Phosphorylation

Vocabulary flashcards covering enzyme regulation, cellular respiration stages, mitochondrial structures, electron carriers, and oxidative phosphorylation based on Lecture 9 notes.

Competitive Inhibitor

An inhibitor that binds directly to the active site of an enzyme, preventing the normal substrate from binding.

Noncompetitive Inhibitor

An inhibitor that binds to an enzyme somewhere other than the active site, changing the enzyme's shape and decreasing its activity.

Catalytic Subunit

The portion of a multi-subunit enzyme that performs the actual enzymatic reaction.

Regulatory Subunit

The portion of a multi-subunit enzyme to which a regulatory molecule or allosteric inhibitor binds to alter enzyme function.

Allosteric Inhibitor

A regulatory molecule that binds to a regulatory site or subunit away from the catalytic site, inducing a shape change that inhibits the catalytic subunit.

End-Product Inhibition

A form of negative feedback where the final product of a metabolic pathway inhibits an enzyme that acts earlier in the pathway to prevent wasting energy and materials.

Substrate-Level Phosphorylation

A mode of $ATP$ synthesis in which a phosphate group is directly transferred from a donor molecule to $ADP$.

Glycolysis

An anaerobic metabolic pathway occurring in the cytoplasm that breaks down $1$ glucose molecule ($6$ carbons) into $2$ pyruvate molecules ($3$ carbons each), producing a net yield of $2$ $ATP$ and $2$ $NADH$.

Investment Phase

The first phase of glycolysis in which the cell spends $2$ $ATP$ to initiate the breakdown of glucose.

Splitting Phase

The second phase of glycolysis in which the $6$-carbon glucose intermediate is cleaved into two $3$-carbon molecules.

Payoff Phase

The third phase of glycolysis that occurs twice per glucose molecule, producing $4$ $ATP$ and $2$ $NADH$ to yield a net profit of $2$ $ATP$.

Pyruvate Oxidation

A reaction in the mitochondrial matrix that converts $2$ pyruvates into $2$ acetyl-$CoA$ molecules, producing $2$ $CO_2$ and $2$ $NADH$ per glucose.

Acetyl-CoA

A $2$-carbon molecule produced during pyruvate oxidation that carries carbon units into the citric acid cycle.

Oxaloacetate

The $4$-carbon acceptor molecule in the citric acid cycle that combines with $2$-carbon acetyl-$CoA$ to form citrate and is regenerated at the end of each cycle turn.

Citrate

The $6$-carbon first product formed in the citric acid cycle when $2$-carbon acetyl-$CoA$ joins with $4$-carbon oxaloacetate.

Citric Acid Cycle

A metabolic pathway in the mitochondrial matrix that oxidizes acetyl-$CoA$, regenerating oxaloacetate while producing $CO_2$, $NADH$, $FADH_2$, and $2$ $ATP$-equivalents per glucose.

Mitochondrial Matrix

The innermost compartment of the mitochondrion enclosed by the inner mitochondrial membrane, where pyruvate oxidation and the citric acid cycle occur.

Intermembrane Space

The region between the outer and inner mitochondrial membranes where protons ($H^+$) are pumped by the electron transport chain to build a concentration gradient.

Complex I

The first protein complex of the electron transport chain, which accepts high-energy electrons directly from $NADH$.

Complex II

The protein complex of the electron transport chain through which $FADH_2$ donates its electrons.

Coenzyme Q (CoQ)

A mobile electron carrier in the inner mitochondrial membrane that transports electrons from Complex I and Complex II to Complex III.

Cytochrome c

A mobile electron carrier that transfers electrons from Complex III to Complex IV in the electron transport chain.

Molecular Oxygen ($O_2$)

The strongly electronegative final electron acceptor of the electron transport chain that accepts electrons from Complex IV and combines with protons to form $H_2O$.

Proton Gradient

An electrochemical gradient created by pumping $H^+$ into the intermembrane space, storing potential energy used to drive $ATP$ synthesis.

ATP Synthase

A membrane-bound protein complex that uses the kinetic energy of protons ($H^+$) flowing down their concentration gradient to catalyze the conversion of $ADP$ and $P_i$ into $ATP$.

$F_0$ Subunit

The membrane-embedded portion of ATP synthase that forms a proton channel and rotates as protons ($H^+$) pass through it from the intermembrane space to the matrix.

$F_1$ Subunit

The catalytic portion of ATP synthase located in the mitochondrial matrix that changes shape as the $F_0$ shaft rotates to synthesize $ATP$ from $ADP$ and $P_i$.

Oxidative Phosphorylation

The process occurring at the inner mitochondrial membrane where the electron transport chain and ATP synthase collaborate to generate approximately $26$\text{--}$28$ $ATP$ per glucose molecule.