Biochemistry Practice: Metabolism and Energy Production

Flashcards covering the metabolic pathways including the citric acid cycle, electron transport chain, glycogen synthesis, fatty acid metabolism, and cholesterol regulation.

Mitochondrial pyruvate carrier

A transmembrane protein that transports pyruvate into the mitochondria to produce acetyl CoA for the citric acid cycle.

PDH Complex

An irreversible multienzyme complex in animal cells that converts pyruvate to acetyl CoA by removing $CO_2$ and two electrons (forming NADH), and then adding an acetyl group to CoA via a thioester linkage.

TPP ($B_1$ + 2 Phosphates)

The prosthetic group associated with enzyme E1 (PDH Component) within the PDH Complex.

Lipoamide

The prosthetic group for enzyme E2 (Dihydrolipoyl transacetylase) that acts as a 'swinging arm' during the transformation of pyruvate.

Citrate synthase

The enzyme that combines an acetyl group ($C_2$) with oxaloacetate ($C_4$) to produce citrate ($C_6$) in the first step of the citric acid cycle.

Aconitase

The enzyme that moves a hydroxyl group from $C_3$ to $C_2$ to convert citrate into isocitrate.

Isocitrate dehydrogenase

The enzyme responsible for the first committed step of the citric acid cycle, converting isocitrate to alpha-ketoglutarate by removing H and forming $C_2=O$.

Succinyl CoA synthetase

The enzyme that breaks a thioester bond in succinyl CoA to form ATP and succinate.

Malate dehydrogenase

The enzyme that removes H from malate to create $C_2=O$, thereby regenerating oxaloacetate.

Complex 1 (NADH-coenzyme Q reductase)

The ETC complex that pumps $H^+$ as it oxidizes NADH to $NAD^+$ and transfers electrons to Coenzyme Q using flavin mononucleotides.

Complex 2 (Succinate Q-Reductase)

The ETC complex where $FADH_2$ is oxidized to FAD to pass electrons to Coenzyme Q (ubiquinone) without pumping any $H^+$ protons.

Complex 4

The final complex in the electron transport chain that pumps $H^+$ and facilitates the reduction of $O_2$ to $H_2O$.

ATP Synthetase (Complex 5)

The complex responsible for synthesizing ATP from ADP and $P_i$, consisting of the $F_0$ subunit (a, $b_2$, c) and the $F_1$ subunit ($ext{alpha}$, $ext{beta}$, $ext{gamma}$, $ext{epsilon}$, $ext{delta}$).

Tight (T) State

The conformation of the alpha-beta dimer in the ATP synthase hexamer where ATP is actively synthesized.

ATP-ADP translocase

A membrane protein powered by the proton motive force that couples the entry of ADP into the mitochondrial matrix with the exit of ATP.

Glycerol 3-phosphate shuttle

The NADH shuttle mechanism used specifically by muscle cells.

Malate-aspartate shuttle

The shuttle used by the heart and liver to generate mitochondrial NADH.

alpha-1,6 linkages

The chemical bonds that form the branch points in a glycogen molecule.

Glycogen phosphorylase

The enzyme that breaks alpha-1,4 linkages in glycogen by adding a phosphate group, producing glucose 1-phosphate.

Glycogenin

The starter protein required to begin the synthesis of a new glycogen chain.

Glycogen synthase

The key regulatory enzyme in glycogen synthesis that transfers glucose to the $C_4$ end of a glycogen chain; it is active in the dephosphorylated 'a' state.

Beta oxidation

The mitochondrial process of breaking down fatty acids into acetyl CoA through four steps: activation by CoA, transport via carnitine, oxidation, and thiolysis.

D3-Hydroxybutyrate

A ketone body considered superior for energy because it is a more reduced version that yields an extra NADH upon utilization.

ACC1 (Acetyl CoA Carboxylase 1)

The regulatory enzyme for fatty acid synthesis in the cytosol that converts acetyl CoA into malonyl CoA; it is activated by insulin and citrate.

Pentose Phosphate Pathway

A pathway that produces NADPH for biosynthesis and 5-carbon sugars (ribose 5-phosphate) for nucleotide synthesis.

HMG-CoA reductase

The rate-limiting regulatory enzyme in cholesterol synthesis that converts 3-hydroxy-3-methylglutaryl CoA into mevalonate.

LDL (Low-Density Lipoprotein)

The major carrier of cholesterol in the blood; high levels are associated with atherosclerosis when oxidized and ingested by macrophages.

PCSK9

A protein that regulates LDL levels by preventing the recycling of LDL receptors back to the cell surface.