Feeding, Fasting and Exercise Flashcards
How is food metabolised/ which pathways?
-Oxidative pathways/ catabolic pathways
=Produce intermediates for growth
=CO2, energy (liberated and trapped, used in biosynthetic reactions)
reducing power (trapped in reduced coenzymes, used in anabolic/ biosynthetic pathways)
What are the coenzymes?
- Link catabolic to anabolic pathways
- ATP
- NADP
Describe ATP
- nucleotide, hydrolysis, free energy= -31 kJ/mol, actual free energy in cells= 60 kJ/mol, 40% efficiency
- Glucose= glycolytic pathway, fatty acids= beta-oxidation, amino acid breakdown pathways- terminal pathway of oxidation= tricarboxylic acid cycle with associated mitochondrial electron transport chain
- ATP used for muscle contraction (directly by myosin ATPase), ion translocation across the membrane by pumps to form ion gradients
Describe NADP
-Oxidised state and reduced state
-Carries 2 electrons from 2 hydrogens
NADP+ + 2H= NADPH + H+
-Currency of reducing power
-Pentose phosphate pathway reduces NADP
-Reoxidised in biosynthetic pathway- fatty acid and cholesterol synthesis
-Anti-oxidant function as removes products of oxidation by reactive oxygen species
What is the total energy requirements in humans?
Baby= 2.5 MJ/day, 360 kJ/kg/day
- Increases total requirement until adult, decreases relative body weight
- Depends on exercise/ arduous worker
What are the energy sources in a typical diet?
Carbohydrate (50%)
Fat (33%)- most energy yield (almost completely fully reduced)
Protein (modest amount)
Alcohol?- big energy yield, interferes with metabolism, vitamin deficiencies
What are the advantages and disadvantages of different energy stores in the body?
-Plasma glucose =Can be used by all tissues =Available store is very small -Glycogen =Rapidly mobilised =Can supply energy quickly and anaerobically =Hydrated- weight limits size of energy store -Triacylglycerol =High reduced, big energy yield =Not hydrated, no weight penalty =largest energy-store in body =Cannot be metabolised anaerobically =Fatty acids cannot be used by brain -Protein =Big store =Can be converted to glucose and ketone bodies =All functional- breakdown leads to loss of function
Describe glycogen breakdown/ glycogenolysis
- Yields glucose 1-phosphate (metabolised in glycolytic pathway)
- Either directly metabolised to pyruvate. oxidised to acetyl CoA and further oxidised in mitochondria
- Or pyruvate reduced to lactate (anaerobic)
Describe triacylglycerol breakdown
-Triacylglycerol - major form of fat, ester of glycerol with 3 fatty acids
-Lipolysis releases these as free fatty acids into plasma
-TAG stored in adipose tissue, circulating fatty acids taken up by tissues
-Oxidised in beta-oxidation pathway to acetyl-coenzyme
-Starvation= concentration of free fatty acids rise, acetyl-CoA diverted to ketone bodies
(liver)
Describe protein breakdown
- Proteolytic enzymes, release amino acids
- Each amino acid has different breakdown pathway
- Some converted into glucose= gluconeogenic amino acids
- Amino acids= acetyl-CoA= ketogenic amino acids as increase concentration of ketone bodies in starvation
- Acetyl CoA= principle fuel of terminal oxidation pathway
- Acetyl groups totally oxidised to CO2, process produces a lot of ATP but requires oxygen
Describe glucose as a fuel
- 6 carbon sugar that circulates in plasma
- Concentration maintained within relatively tight levels (glucose homeostasis)
- Brain oxidises glucose, 120 grams
- Erythrocytes metabolise only glucose, to lactate
- Demand met by glycogen degradation in fasting
Describe fatty acids as a fuel
- Not very soluble, largely bound to albumin
- 0.1 millimole per litre
- Rises during fasting
Describe ketone bodies as a fuel
- Acetoacetate and 3-hyrdoxy butyrate
- Derived from acetyl-CoA coming from fatty acid breakdown
- Low in fed state, rises during fasting
- String acids, acid-base imbalance, metabolic acidaemia
Describe amino acids
Total concentration in plasma= 4 millimoles per litre
-Not in equal concentration
20
Describe lactate
- Anaerobically oxidising glucose or in red blood cells
- Circulates at relatively low levels
What are the types of muscle fibre?
Red= aerobic= slow contraction rate, high myoglobin content (oxygen storage), low myosin ATPase activity, low creatine kinase activity, high mitochondrial oxidation rate, low glycolytic rate White= fast contraction rate, low myoglobin content, high myosin ATPase activity, high creatine kinase activity, low mitochondrial oxidation rate, high glycolytic rate
What is creatine phosphate?
- Small energy store within muscle
- Contains relatively high concentrations of ATP (5-10mmol/l)
- Phosphagen= attached phosphate group transferred to ADP, releasing creatine
- ATP hydrolysed ADP by myosin ATPase, can be re-phosphorylated back to ATP therefore creatine phosphate acts as buffer of ATP
What are the fuels for muscle contraction in purely anaerobic exercise (sprinting)?
- Muscle ATP
- Creatine phosphate
- Muscle glycogen
What are the fuels for muscle contraction in purely aerobic exercise (marathon running)?
- ATP, creatine-P, muscle glycogen
- Fatty acids (muscle and adipose tissue)
- Plasma glucose (from liver glycogen and gluconeogenesis)
Describe glucose metabolism in the muscle
- Mobilised hormonally, stimulated by glucagon, adrenalin, increase in AMP concentration
- Broken down into glucose 1-phosphate which is isomerised to glucose-6-phosphate that can be broken down anaerobically to pyruvate, pyruvate reduced to lactate
- 1 molecule glucose to 2 lactates so 2 ATP (dismutation reaction= no oxygen required)
- With oxygen= pyruvate enters mitochondria= oxidised to acetyl-CoA= TCA cycle completely to CO2- 30 ATPs per mol of glucose
What happens to lactate?
- Enters plasma and circulates
- Some tissues= converted back to glucose by gluconeogenesis (liver and kidney)- requires 6 ATPs to reverse glycolysis
How is metabolism controlled during exercise?
ADP= dismutation reaction catalysed by adenylate kinase/ myokinase= AMP (adenosine monophosphate) and ATP
- AMP= control feature through AMP-activated protein kinase, phosphorylated to activate (kinases= phosphorylation)
- Can activate phosphatases (remove phosphates)
- Activates degradative pathways and inactivates biosynthetic pathways
What are the metabolic effects of AMP-activated protein kinase?
- Activates= glucose uptake, glycolysis, fatty acid oxidation, mitochondrial biogenesis
- Inhibits= gluconeogenesis, cholesterol synthesis, glycogen synthesis, fatty acid synthesis, protein synthesis
