Energy Metabolism Flashcards
Glycolysis
1) glucose is converted to fructose-1,6-bisphopshate via hexakinase and phosphofructokinase, consuming 2ATP
2) glyceraldehyde 3-phosphate dehydrogenaae produces 2NADH
3) phosphoglycerate kinase produces 2ATP
4) in the last step, pyruvate kinase produces 2ATP and pyruvate
The TCA cycle
1) pyruvate moves into mitochondria via pyruvate carrier, converted to acetyl CoA by pyruvate dehydrogenase; producing 2NADH and CO2. Cycle begins.
2) isocitrate dehydrogenase converts isocitrate to alpha-ketoglutarate which produces 2NADH+CO2
3) alpha-ketoglutarate dehydrogenase then reduces to succinyl CoA, producing 2NADH+CO2
4) succinyl CoA synthetase catalyses conversion to succinate which liberates 2GTP
5) succinate dehydrogenase produces fumarate from succinate yielding 2FADH for complex II
6) malate dehydrogenase converts malate to oxaloacetate yielding 2NADH
YIELD: 8NADH + 2FADH + 2GTP
Electron transport chain
- electrons produced from TCA cycle and glycolysis move to the cristae in the mitochondria
- complex I: NADH deposits 2 e, which move down redox centers from high-> affinity; and transfer to ubiquinone (coenzyme Q10) for transfer to complex III. 4H+ are pumped from the matrix to the intermembrane space
- complex II: FADH donates e, which are transferred to ubiquinone and complex III
- complex III: through redox centers, transfer e- to cytochrome C. Pumps 2H+ to intermembrane space
- complex IV: accepts e from cytochrome C, pumps 2H+
- F0F1 ATP synthease: 3H+ moves from intermembrane space to matrix. 3 proteins in channel, bound to ATP or ADP+Pi or empty. Process relies on ability for membrane potential to be formed (concentration, pH and charge), due to impermeability of membrane
Uncouplers
- molecules which breakdown proton gradient. Inhibit the ability to form ATP
- dinitrophenol: fat burning pill. Couples to H+ and carries from the intermembrane space back to matrix
- natural uncouplers: UCP-1 in infants (<1 year); upregulated in times of cold to produce heat
Anerobic respiration
- following glycolysis, pyruvate is formed along with 2ATP
- produces lactate via pyruvate dehydrogenase using NADH
- lactate transported to liver, where it is converted back to pyruvate (via the Cori cycle) then to glucose via gluconeogenesis
- inefficient way of producing energy
The Warburg effect for proliferating tissues
- cancer cells metabolise glucose via aerobic glycolysis producing lactate from pyruvate
- inefficient way of producing energy but aims to produce carbon biomass from glucose for cell walls of daughter cells
Contraction of muscle fibres
- structure: sarcomere, parallel Z lines, thin filaments (actin) overlap with thick filaments (myosin, an enzyme) in the H zone (the A band). Actin alone is the I band
- ATP added to the myosin head causes it to detach from actin filament, and hydrolyse to ADP and Pi
- addition of H20 causes rebinding
- after gripping, power stroke then moves the actin causing contraction
Attwater factors
- focus on digestibility coefficient
- CHO: 4 kcals/g
- protein: 4 kcals/g
- alcohol: 7 kcals/g
- fat: 9 kcals/g
Factors affecting energy expenditure
- Basal metabolic rate: 60-75%, affected by age, FFM. Contributes to Na+ and K+ pump, protein turnover
- thermic effect of food: fibre intake, energy produced during digestion
- physical activity: dependent on type and environment
Ways of measuring energy expenditure
- gold standard: indirect measures with gas mask measuring O2 consumption, and CO2 release using doubly-labelled water
- metabolic equivalents, can quantify using Weir equation in mL/min:
REE= 1.44 x (3.94 x VO2) + (1.1 x CO2)
Exercise effects on EPOC and RMR
- EPOC: post energy oxygen consumption
- increases hours after exercise
- replenishing O2 stores, for resynthesis of ATP, protein turnover
Main elements of skeletal muscle
- muscle connected to bone via tendons
- myofibril is split into two z lines with thin (actin) and thick (myosin) between
- desmin protein links up to z lines
- dystrophin protein links actin filaments to sarcolemma
- costameres link myofibril to cell membrane, bound to dystrophin
Muscle fiber types
- type I: slow oxidative, primarily uses glucose and fatty acids for oxidative metabolism. Slow twitch. High levels of capillaries. Endurance events
- type IIA: fast oxidative glycolytic, can do oxidative or anerobic. Used for hypertrophy training
- type IIB: fast glycolytic, fast twitch. Fatigues quickly, produces lactate and utilizes glucose via glycolysis
Elements of exercise metabolism: maintaining ATP concentration
- phosphocreatinine quickly used up, kinase releases phosphate for ATP regeneration
- calcium release from sarcoplasmic recticulum binds to phosphorylase kinase b stimulating activation and phosphorylation of glycogen to glucose
- catecholamines activate pathways relating to lipolysis and glycogenolysis
- AMP kinase is activated from high intracellular AMP concentrations, which facilitates fatty acid uptake into cells via CD34 and non-insulin mediated exocytosis of GLUT4
Effects of hypoglycaemia
- seizures
- coma
- brain damage
- death
Blood glucose of 4 mM is hypoglycaemic threshold
3mM will start having autonomic symptoms (sweating, tremor)
2 mM glycopenic symptoms (confusion, drowsiness)
1.5 mM hypoglycaemia unawareness
