Topic 2: Energy Pathways & Exercise Metabolism — VOCABULARY Flashcards

Vocabulary flashcards covering key terms and definitions from Topic 2: Energy Pathways & Exercise Metabolism, including the phosphagen, glycolytic, and oxidative systems; substrates and energy yield; transport and regulation of fuels; and hormonal regulation of substrate mobilization.

Metabolism

All chemical processes in a living organism; includes aerobic and anaerobic reactions that convert substrates to energy (ATP).

Bioenergetics

Flow of energy through a biological system and the chemical pathways that convert substrates into usable energy (ATP).

Phosphagen energy system

An immediate, short-duration energy system that uses phosphocreatine (PCr) to rapidly regenerate ATP (approximately 0–15 seconds).

Glycolytic energy system

Energy system that rapidly produces ATP from glucose/glycogen, does not require oxygen, and operates in the 15 seconds to ~2 minutes range; end products can be pyruvate or lactate.

Oxidative energy system

Energy system that produces ATP via acetyl-CoA substrates through the TCA cycle and electron transport chain; slower but can sustain energy for extended periods (2+ minutes).

Phosphocreatine (PCr)

A high-energy phosphate compound used with ADP to quickly regenerate ATP during the phosphagen system.

Creatine kinase

Enzyme that transfers a phosphate from PCr to ADP to form ATP and creatine during rapid energy demand.

Adenylate kinase

Enzyme that converts two ADP molecules into ATP and AMP, contributing to rapid energy buffering.

ATP (adenosine triphosphate)

The immediate energy currency of the cell; energy stored in phosphate bonds and renewed during metabolism.

NADH (nicotinamide adenine dinucleotide, reduced)

Electron carrier produced in glycolysis and the TCA cycle; donates electrons to the electron transport chain (ETC) for ATP production.

NAD+ (nicotinamide adenine dinucleotide, oxidized)

Oxidized form of NADH; accepts electrons during metabolic reactions to form NADH again.

FADH2

Electron carrier produced in the TCA cycle; donates electrons to the ETC for ATP production (less ATP per molecule than NADH).

Pyruvate

End product of glycolysis; can be converted to acetyl-CoA for entry into the TCA cycle or reduced to lactate under anaerobic conditions.

Lactate

Reduced form of pyruvate formed when NADH accumulates; lactate can be recycled back to pyruvate or oxidized via the lactate shuttle to sustain glycolysis.

Lactate dehydrogenase (LDH)

Enzyme that converts pyruvate to lactate (and vice versa), helping regenerate NAD+ for glycolysis under oxygen-limited conditions.

Pyruvate dehydrogenase (PDH)

Enzyme complex that converts pyruvate to acetyl-CoA, linking glycolysis to the TCA cycle in the mitochondria.

Acetyl-CoA

A central metabolic substrate produced from pyruvate (via PDH) or fatty acids; enters the TCA cycle to generate energy.

TCA cycle / Krebs cycle

Midpoint of aerobic metabolism where acetyl-CoA is oxidized to CO2, generating NADH, FADH2, and GTP for ATP production.

Electron Transport Chain (ETC)

A series of protein complexes in the inner mitochondrial membrane that transfer electrons from NADH and FADH2 to O2, creating a proton gradient to drive ATP synthesis.

Oxidative phosphorylation

Process of ATP production when electrons are transferred through the ETC and proton gradient drives ATP synthase.

Glycogenolysis

Breakdown of glycogen to glucose-1-phosphate, feeding glycolysis in muscle (costs 0 ATP when derived from glycogen).

Glycolysis

Metabolic pathway converting glucose/glycogen to pyruvate (or lactate) with net production of 2 ATP (from glucose) or 3 ATP (from glycogen) and generation of NADH.

Glycolysis rate-limiting step (PFK)

Fructose-6-phosphate to fructose-1,6-bisphosphate step controlled by phosphofructokinase (PFK); activated by AMP, inhibited by H+.

Glucose transport (GLUT4)

Transmembrane transporter that moves glucose into muscle cells, regulated by insulin and exercise-induced signals via GLUT4 translocation.

Hexokinase

Enzyme that phosphorylates glucose to glucose-6-phosphate at the start of glycolysis.

Lipolysis

Breakdown of triglycerides into glycerol and free fatty acids (FFAs); stimulated by catecholamines, cortisol, glucagon, and growth hormone; inhibited by insulin.

Free fatty acids (FFA)

Fatty acids released from adipose tissue during lipolysis; transported in blood bound to albumin to muscle for oxidation.

Carnitine shuttle (CPT1/CPT2)

Transport system that moves long-chain fatty acyl-CoA into mitochondria for beta-oxidation via carnitine intermediates.

Beta-oxidation

Mitochondrial process that cleaves fatty acids into two-carbon acetyl-CoA units; generates NADH and FADH2 for the ETC but produces no net ATP directly from fatty acids.

Palmitic acid oxidation ATP yield

Complete oxidation of palmitate (16-carbon fatty acid) yields around 106 ATP through beta-oxidation and subsequent pathways.

Ketogenic, alcohol and biosynthetic pathways

Metabolic routes that can contribute to energy supply or substrate availability; include alcohol oxidation and amino-acid–derived and biosynthetic pathways active during exercise under certain conditions.

Amino acid oxidation

Use of amino acids for energy via deamination and entry into TCA or gluconeogenesis; ATP yield varies by amino acid type.

Amino acid deamination/transamination

Removal of amino group (deamination) or transfer of amino group (transamination) to form other metabolites (e.g., glutamate) and enter energy pathways.

Athlete paradox

Observation that endurance athletes can have high intramyocellular lipid content yet high oxidative capacity and insulin sensitivity.

Epinephrine (adrenaline)

Hormone that stimulates lipolysis and mobilizes fat stores during exercise; part of the fight-or-flight response to increase energy availability.

Norepinephrine (noradrenaline)

Sympathetic hormone that promotes lipolysis and energy mobilization during exercise.

Glucagon

Hormone that raises blood glucose by promoting glycogenolysis and gluconeogenesis; supports energy availability during fasting or prolonged exercise.

Cortisol

Glucocorticoid hormone that supports energy metabolism during stress; promotes gluconeogenesis and lipolysis.

Growth hormone

Hormone that supports lipid mobilization and can influence substrate availability during long-duration exercise.

Albumin

Plasma protein that transports free fatty acids in the bloodstream to tissues like exercising muscle.

FAT/CD36 and FABPpm

Fatty acid transporters on muscle cell membranes that help import FFAs into muscle for oxidation.

Glycerol

Backbone from triglycerides; released during lipolysis and can be used for gluconeogenesis.

Glycogen storage and exercise

Diet and training influence muscle glycogen stores, affecting endurance performance and fuel availability.

ATP yield from carbohydrate oxidation

Aerobic breakdown of glucose/glycogen yields about 32 ATP per glucose (33 ATP per glycogen) when fully oxidized in the ETC.

Oxygen role in metabolism

Oxygen acts as the final electron acceptor in the ETC; without it, aerobic ATP production is limited.