Nutrition and Metabolism - Carbohydrate metabolism

Glucose catabolism

A process accomplished in small steps, each controlled by a separate enzyme, in which energy is released in small manageable amounts, and as much as possible, is transferred to ATP and the rest is released as heat.

Glycolysis

A metabolic pathway that splits one glucose molecule into two molecules of pyruvate.

Anaerobic fermentation

A pathway that reduces pyruvate to lactate without using oxygen.

Aerobic respiration

A process that requires oxygen and oxidizes pyruvate to carbon dioxide and water.

$NAD^+$ (nicotinamide adenine dinucleotide)

A coenzyme that binds two electrons but only one proton to become $NADH$; the other proton remains a free hydrogen ion ($H^+$).

$FAD$ (flavin adenine dinucleotide)

A coenzyme that binds two protons and two electrons to become $FADH_2$.

Phosphorylation

The first step of glycolysis where the hexokinase enzyme transfers an inorganic phosphate group from ATP to glucose, producing glucose 6-phosphate ($G6P$).

Glucose 6-phosphate ($G6P$)

A phosphorylated compound that cannot pass through the cell membrane, keeps intracellular glucose concentration low, and can be converted to fat, amino acids, glycogen, or oxidized.

Priming

The steps in glycolysis where $G6P$ is rearranged to fructose 6-phosphate and phosphorylated again to form fructose 1,6-diphosphate, providing activation energy.

Cleavage

The stage of glycolysis where fructose 1,6-diphosphate lyses or splits into two three-carbon molecules known as $PGAL$.

$$PGAL$$

Phosphoglyceraldehyde (also called glyceraldehyde 3-phosphate), which are the two $C_3$ molecules produced after the cleavage step in glycolysis.

Dephosphorylation

The step in glycolysis where phosphate groups are taken from intermediates and added to ADP to create ATP, resulting in the formation of pyruvate.

Net gain of glycolysis

The production of $2$ ATP per glucose molecule ($4$ ATP produced minus $2$ ATP consumed).

Lactate

The product of anaerobic fermentation formed when $NADH$ donates electrons to pyruvate, which also regenerates $NAD^+$.

Postexercise oxygen consumption

The reason for breathing more vigorously after exercise, as oxygen is required by the liver to oxidize lactate back to pyruvate.

Matrix reactions

Mitochondrial reactions whose controlling enzymes are in the fluid of the mitochondrial matrix; includes the preparation of pyruvate and the citric acid cycle.

Membrane reactions

Mitochondrial reactions whose controlling enzymes are bound to the membranes of the mitochondrial cristae.

Decarboxylation

A matrix reaction step where $CO_2$ is removed from pyruvate to make a $C_2$ compound.

Acetyl-coenzyme A (acetyl-CoA)

The result of an acetyl group binding to coenzyme A, which then enters the citric acid cycle.

Citric acid cycle (Krebs cycle)

A series of matrix reactions starting when acetyl-CoA combines with oxaloacetic acid ($C_4$) to form citric acid ($C_6$).

Mitochondrial electron-transport chain

A series of compounds, mostly bound to the inner mitochondrial membrane, that further oxidize $NADH$ and $FADH_2$ and transfer their energy to ATP.

Metabolic water

Water synthesized in the body when oxygen, acting as the final electron acceptor, accepts two electrons and two protons.

ATP synthase

Channel proteins in the inner mitochondrial membrane through which $H^+$ icons rush back into the matrix, driving the synthesis of ATP.

Chemiosmotic mechanism

The process where the energy from the electron-transport chain fuels proton pumps to create a gradient, and the subsequent $H^+$ current through ATP synthase drives ATP synthesis.

Efficiency of aerobic oxidation

The complete aerobic oxidation of glucose to $CO_2$ and $H_2O$ produces $32$ ATP, representing an efficiency rating of 34\text{%}.

Metabolism

The set of life-sustaining chemical reactions in organisms, involving energy production and utilization.

Three main pathways of glucose metabolism

Glycolysis, citric acid cycle, and oxidative phosphorylation.

Oxidation in metabolism

The process of losing electrons or hydrogen, often associated with the release of energy.

Reduction in metabolism

The process of gaining electrons or hydrogen, typically storing energy.

Coenzyme

A non-protein molecule that aids enzyme function, often by facilitating the transfer of electrons or atoms.

Oxidation stage of glycolysis

The step in glycolysis where $PGAL$ is oxidized, leading to the formation of $NADH$.

Four end products of glycolysis

Two molecules of pyruvate, two molecules of ATP, two molecules of NADH, and water.

Cell glycolysis

The entire process of glycolysis occurring within the cytoplasm of cells to produce energy.

Proton gradient

The difference in proton concentration across a membrane, crucial for ATP synthesis in mitochondria.