Cellular Energetics 8/10 Flashcards
amphibolic
biochemical process that involves both anabolism and catabolism
TCA cycle is amphibolic because
involved in aerobic catabolism of carbs, lipids, amino acids; intermediates of TCA are starting points for many anabolic reactions
anabolic reactions
transfer energy from ATP to complex molecules (endergonic, reduction)
catabolic reactions
transfer energy from complex molecules to ATP (exergonic, oxidation)
rate limiting step of glycolysis
conversion of fructose-6-phosphate to fructose-1,6-bisphosphate by phosphofructokinase 1. (Also converts ADP to ATP)
steps in glycolysis with substrate level phosphorylation
- phosphoglycerate kinase converts 1,3-BPG to phosphoenolpyruvate, ADP->ATP
- pyruvate kinase converts phosphoenolpyruvate to pyruvate, ADP->ATP
glycolysis ATP yield
produces 2 ATP in anaerobic conditions, 7 ATP in aerobic conditions (because each NADH = 2.5 ATP)
glycolysis substrates
2 ATP, 2 NADH, and 2 pyruvate molecules
NADH ATP yield
10 H+ ions = 2.5 ATP per NADH
FADH2 ATP yield
6H+ ions = 1.5 ATP per FADH2
Complex I
complex of ETC in which NADH transfers 2e- to Q. Q is reduced to Qh2, NADH oxidized to NAD+. 4 H+ ions pumped across membrane, establishing the H+ gradient.
Complex II
complex of ETC in which FADH2 transfers e- directly to Q, bypassing complex 1. FADH2 is oxidized to FAD, Q reduced to Qh2. Qh2 directly delivers the e- from complex 1 and 2 to complex 3. No H+ ions are pumped from this complex.
Complex III
complex of ETC in which Qh2 transfers e- to cytochrome C. H+ ions are pumped into intermembrane space, contributing to the gradient. Cytochrome C can only accept one electron at a time.
Complex IV
complex of ETC in which the final H+ ions are pumped across the membrane. Electrons are passed from cytochrome C to the final electron acceptor, oxygen. O2 splits and each O takes 2H+ ions from the matrix, forming 2 molecules of H2O.
Complex V (ATP synthase)
final stage of ETC. H+ ions are pumped through ATP synthase against their gradient, generating energy in the form of ATP.
adenylate kinase
enzyme that catalyzes the interconversion of adenine dinucleotides: 2ADP AMP + ATP.
Signals to AMP sensors to increase ATP consumption or production.
Uses anabolic and catabolic reactions to maintain adenylate charge at metabolic steady state ~0.9.
adenylate charge
= [ATP] + 0.5 [ADP] / [ATP] + [ADP] + [AMP]
transphosphorylation
high energy compounds can recycle ATP by coupling to ADP. They must have more negative free energy of hydrolysis than ATP to catalyze the phosphorylation of ADP to ATP.
Ex: creatine phosphate + ADP -> creatine + ATP, deltaG= -3 kcal/mol.
Ex: phosphocreatine and ADP couple to replenish ATP in skeletal muscles (catalyzed by creatine kinase)
Why are fats more caloric than carbs?
fats are more reduced than carbs, thus they require greater oxygen for hydrolysis and thus release more energy (9kcal/g vs 4 kcal/g)
Respiratory quotient (RQ)
measure of the ratio of CO2 produced to O2 consumed by an organism.
= amt CO2 produced/amt O2 consumed.
*valuable because gives info regarding the nature of the substrate being used for energy. Fat = 0.7, Carb = 1.0, Protein = 0.82, mixed feeding = 0.85, overfeeding = 1.1-1.2.
TCA cycle substrates
pyruvate, citrate, isocitrate, alpha ketoglutarate, succinyl coA, succinate, fumarate, malate, oxaloacetate
enzymes of TCA that convert NAD+ to NADH
isocitrate dehydrogenase, alpha ketoglutarate dehydrogenase, malate dehydrogenase
enzyme of TCA that converts FAD to FADH2
succinate dehydrogenase
tricarboxylate transporter
exchanges a citrate made in the mitochondrial matrix during the TCA cycle for a malate (citrate ends up in cytoplasm); citrate is converted back to Acetyl coA (by ATP citrate lyase) for fatty acid synthesis in the cytoplasm of the cell.
*citrate in cytoplasm also blunts glycolysis by inhibiting PFK-1.
**inhibitors of tricarboxylate transporter reduce fatty acid synthesis.
