Energy, Chemical Reactions, and Cellular Respiration

Vocabulary terms and definitions covering metabolic pathways, enzyme regulation, and the stages of cellular respiration including glycolysis, the citric acid cycle, and the electron transport system.

Metabolic pathway

A series of enzymes where the product of one enzyme becomes the substrate of the next; for example, the chemical breakdown of glucose.

Multienzyme complex

A group of attached enzymes that work in a sequence of reactions, such as pyruvate dehydrogenase involved in the breakdown of glucose.

Negative feedback (in metabolic pathways)

A regulatory mechanism where the end product of a pathway acts as an allosteric inhibitor to turn off an enzyme early in the pathway.

Phosphorylation

The addition of a phosphate group to an enzyme, performed by phosphorylases or kinases, which can turn some enzymes on and others off.

Dephosphorylation

The removal of a phosphate group from an enzyme, performed by phosphatases.

Pravastatin

A statin medication that inhibits the liver enzyme responsible for cholesterol synthesis to lower the risk of heart attack and stroke.

Lactose Intolerance

A condition caused by a deficiency in lactase, the enzyme required to break the bond in lactose into glucose and galactose.

Cellular Respiration

An exergonic multistep metabolic pathway where organic molecules are oxidized and disassembled by enzymes to release energy for synthesizing ATP.

Glucose oxidation

The step-by-step breakdown of glucose with energy release, forming carbon dioxide ($CO_2$) and water ($H_2O$).

Substrate-level phosphorylation

The least common method of ATP production, where energy from broken bonds is used directly to attach a phosphate group to ADP.

Oxidative phosphorylation

The most common method of ATP production, where energy is first released to coenzymes and then transferred to form ATP.

Glycolysis

An anaerobic metabolic process occurring in the cytosol that breaks down glucose into two pyruvate molecules, resulting in a net production of $2$ ATP and $2$ NADH.

Phosphofructokinase (PFK)

An enzyme in glycolysis that is regulated by negative feedback; it is inhibited by ATP acting as an allosteric inhibitor.

Cristae

The internal folds of the inner mitochondrial membrane where molecules of the electron transport system are embedded.

Matrix

The innermost space of a mitochondrion where the multienzyme complex of the intermediate stage and the enzymes of the citric acid cycle reside.

Intermediate Stage

The link between glycolysis and the citric acid cycle catalyzed by pyruvate dehydrogenase, where pyruvate and coenzyme A (CoA) combine to form acetyl CoA.

Decarboxylation

A process during the intermediate stage where a carboxyl group is released from pyruvate as $CO_2$.

Citric Acid Cycle

A cyclic metabolic pathway in the mitochondrial matrix that produces $1$ ATP, $3$ NADH, and $1$ FADH_2 per turn ($2$ turns per glucose molecule).

Electron Transport System (ETS)

A series of $H^+$ pumps and electron carriers located in the cristae that use energy from NADH and $FADH_2$ to establish an $H^+$ gradient for ATP production.

ATP synthase

An enzyme that harnesses the kinetic energy of $H^+$ moving down its concentration gradient into the matrix to bond ADP and $P_i$, producing ATP.

Cyanide Poisoning

A condition where cyanide binds to a specific electron carrier in the ETS, inhibiting ATP production and preventing electrons from reaching oxygen.

Lactate dehydrogenase

The enzyme that catalyzes the conversion of pyruvate to lactate (lactic acid) when oxygen is insufficient, allowing glycolysis to continue.

Beta oxidation

The process by which fatty acids are enzymatically changed two carbons at a time to form acetyl CoA for entry into the citric acid cycle.

Deamination

The removal of the amine group from amino acids when used as fuel, resulting in a waste product converted to urea and excreted by the kidneys.