Feeding, Fasting and Exercise

Question 1

How is food metabolised/ which pathways?

Answer 1

-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)

Question 2

What are the coenzymes?

Answer 2

• Link catabolic to anabolic pathways
• ATP
• NADP

Question 3

Describe ATP

Answer 3

• 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

Question 4

Describe NADP

Answer 4

-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

Question 5

What is the total energy requirements in humans?

Answer 5

Baby= 2.5 MJ/day, 360 kJ/kg/day

• Increases total requirement until adult, decreases relative body weight
• Depends on exercise/ arduous worker

Question 6

What are the energy sources in a typical diet?

Answer 6

Carbohydrate (50%)
Fat (33%)- most energy yield (almost completely fully reduced)
Protein (modest amount)
Alcohol?- big energy yield, interferes with metabolism, vitamin deficiencies

Question 7

What are the advantages and disadvantages of different energy stores in the body?

Answer 7

-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

Question 8

Describe glycogen breakdown/ glycogenolysis

Answer 8

• 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)

Question 9

Describe triacylglycerol breakdown

Answer 9

-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)

Question 10

Describe protein breakdown

Answer 10

• 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

Question 11

Describe glucose as a fuel

Answer 11

• 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

Question 12

Describe fatty acids as a fuel

Answer 12

• Not very soluble, largely bound to albumin
• 0.1 millimole per litre
• Rises during fasting

Question 13

Describe ketone bodies as a fuel

Answer 13

• 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

Question 14

Describe amino acids

Answer 14

Total concentration in plasma= 4 millimoles per litre
-Not in equal concentration
20

Question 15

Describe lactate

Answer 15

• Anaerobically oxidising glucose or in red blood cells

- Circulates at relatively low levels

Question 16

What are the types of muscle fibre?

Answer 16

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

Question 17

What is creatine phosphate?

Answer 17

• 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

Question 18

What are the fuels for muscle contraction in purely anaerobic exercise (sprinting)?

Answer 18

1. Muscle ATP
2. Creatine phosphate
3. Muscle glycogen

Question 19

What are the fuels for muscle contraction in purely aerobic exercise (marathon running)?

Answer 19

1. ATP, creatine-P, muscle glycogen
2. Fatty acids (muscle and adipose tissue)
3. Plasma glucose (from liver glycogen and gluconeogenesis)

Question 20

Describe glucose metabolism in the muscle

Answer 20

• 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

Question 21

What happens to lactate?

Answer 21

• Enters plasma and circulates

- Some tissues= converted back to glucose by gluconeogenesis (liver and kidney)- requires 6 ATPs to reverse glycolysis

Question 22

How is metabolism controlled during exercise?

Answer 22

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

Question 23

What are the metabolic effects of AMP-activated protein kinase?

Answer 23

• Activates= glucose uptake, glycolysis, fatty acid oxidation, mitochondrial biogenesis
• Inhibits= gluconeogenesis, cholesterol synthesis, glycogen synthesis, fatty acid synthesis, protein synthesis