Physiology Year 2 Flashcards
Possible sites for metabolic limitations to performance
Explosive events
Max effort
Sustained sprinting
What must occur to initiate movement for exercise
Muscles contract when stored chemical energy is converted into mechanical energy
Main source of chemical energy
ATP
How is ATP formed
Formed by bonding inorganic phosphate to ADP
Where is ATP stored and how long can it supply forceful contractions
ATP is stored in the resting muscle throughout the muscle fibres, but particularly in the cross bridge contractile sites
Resting ATP levels can only sustain a few seconds of maximal contraction
Metabolic pathways and their power/duration
Phosphagen system (400kj/min, 10-15s)
Anaerobic glycogenolysis (200kj/min, 45-60s)
Oxidation of glycogen/glucose (125kj/min, 2h)
Fat oxidation (110kj/min, 8h+)
Enzymes
- biological catalyst
- lock and key mechanism
- body temp (37° is optimal working environment)
- enzymes lower activation energy
- a typical mitochondrion may have 10billion
ATP- the ultimate energy currency
- present in small stores within muscles
- 80-100g in body at normal resting levels
- ATP has high energy bonds which when broken down release free energy (30.6kj/mol)
- we synthesise 60kg/day 1500times/day
- synthesise ATP via bioenergetics
- ATPase is responsible for the breakdown of ATP via hydrolysis
- ATP + ATPase ➡️ ADP + P + energy
- forming ATP from ADP is known as phosphorylation. ATP synthase catalyses this process
ATP-PC system
- in addition to small stores of ATP, skeletal muscle contains a larger reserve of a high-energy phosphate compound called phosphocreatine.
- phosphocreatine= 1 creatine molecule and 1 phosphate molecule attached by a high energy bond.
- when hydrolyzed by creatine kinase, phosphate is released and the energy released is used to phosphorylate ADP to ATP
- thus, PCr is an important energy buffer that can maintain muscle ATP levels.
Once PCr is depleted
It’s resynthesized by reversal of the creatine kinase reaction, this phosphorylation energy is derived from oxidative pathways
Anaerobic glycolysis
- breakdown of either muscle glycogen or free glucose to lactate (lactic acid)
- requires 11 chemical reactions, catalysed by enzymes (each one a potential limiting factor)
- 3 ATP molecules are produced for each glycogen broken down to lactic acid (2 ATP for glucose)
- most energy derived from glycogen as glucose conc is lower in muscles
Rate limiting steps (anaerobic glycolysis)
Step 1- initial mobilisation of glycogen to glucose-6-phosphate (glycogen phosphorylase)
Step 3- phosphofructokinase activity is stimulated or inhibited by metabolites (ADP, P or ATP). This is the main limiting factor to glycolysis
Step 11- During high intensity exercise, pyruvate is converted to lactic acid, in the absence of oxygen by lactate dehydrogenase
How can training influence metabolic performance
- with training it’s possible to increase concentration of certain enzymes (phosphorylase, PFK, LDH) and substrates
- muscle glycogen can be increased by training or by a high CHO diet
- in brief efforts, amount of H produced won’t be sufficient to inhibit enzyme reaction rates, yet this may be a factor in repeated efforts
- in repeated exercise bursts, it’s important to train for increased capacity to remove or buffer H ions.
Major adaptations during resistance training
- biggest change in muscular hypertrophy
- increased resting glycogen and PCr
- little effect on glycolytic and oxidative enzymes
Aerobic metabolism
- metabolic pathway for resynthesis of ATP derived from oxidation of pyruvic acid generated by glycolysis or from the oxidation of fatty acids.
- potential energy in the hydrogen electron and proton released through the electron transport chain, which re-phosphorylates ADP to ATP
- final step needs the proton and electron to be reunited and accepted by water. This can only occur in the presence of oxygen
- max rate of ATP generation dependent on max rate oxygen is available to mitochondria
- oxygen supply is the first rate limiting step.
Oxidation and reduction
Oxidation- the removal of hydrogen atoms
Reduction- addition of an electron.
Oxidation and reduction are always coupled reactions
Often involves the transfer of hydrogen atoms rather than free electrons
Hydrogen atom contains one electron
Molecule that loses a hydrogen also loses an electron and therefore is oxidised.
What’s generated from 1 turn of the kerbs cycle
- 1 ATP produced
- 4 pairs of hydrogens removed (3NAD and 1FAD)
- CO2 given off which dissolved in blood
- 12 hydrogen pairs that move into the electron transport chain
NAD carrier coenzymes
- Nicotinamide adenine dinucleotide is a coenzyme found in all living cells.
- exists oxidised and reduced
- NAD carries energy from one reaction to another (accepts electrons from one molecule, becoming reduced NADH so can donate electrons.
During glycolysis and Citric acid cycle, electrons carried by NADH are transferred into the mitochondria by mitochondrial shuttles. Then oxidised in turn by the electron transport chain, which pumps protons across a membrane and generates ATP through oxidative phosphorylation.
Electron transport chain
ETC transfers electrons from electron doners (NADH and FADH) to electron acceptors via redox reactions. Electron transfer is coupled with the transfer of protons across the inner mitochondrial membrane
In a sequence of redox reactions, electrons are passed down a series of iron-containing carriers
In the final step, electrons and protons are reunited to form hydrogen which combines with oxygen to form water
High energy electron is passed through the etc and energy released pumps hydrogen out of the matrix space.
Fat as an exercise fuel (beta oxidation)
- Although ATP generation during high intensity exercise is predominantly glycogen, pathways for fat and protein are also available
- during low to moderate exercise, up to 50% of energy may be made by fats.
Fats stored in muscle and fat cells as triglyceride - triglyceride contains 1 glycerol and 3 fatty acids
- hydrogen rich and energy dense
- fatty acids mobilised by enzyme hormone sensitive lipase in fat cells.
- splits triglyceride into glycerol and fatty acids which enter blood and transported to muscles.
- FFAs combine with coenzyme A, forming acyl-CoA
Carrier protein carburise and carnitine transferase transport fatty acyl CoA into mitochondria. - this is where the fatty acyl CoA undergoes beta oxidation
Fat burning
- the ability to oxidise fats instead of carbohydrates.
- endurance athletes have an increased capacity to oxidise fatty acids
- yet patients with obesity, insulin resistance and type 2 diabetes may have an impaired capacity to oxidise fat.
Fat oxidation peaks at 65% of max heart rate
RER/RQ
- we can estimate the proportional contribution of carbohydrate and fat oxidation
- RER measures the difference between O2 consumed and CO2 produced within whole body
- RQ reflects the ratio of CO2 produced by mitochondria to O2 consumed over the same time
Protein as a fuel source
- pathways exist in muscles that can remove nitrogen from amino acids that can then enter the Krebs cycle.
- or amino acids can be converted to alanine which can in turn be converted in the liver to glucose
- these pathways are more prevalent in starvation to sustain life rather than performance in fed athletes.
- accelerated by decrease in glycogen and blood glucose and increase in cortisol
Rate controlling steps for aerobic metabolism summary
Outside cell:
- oxygen deliver to muscle
- hormone changes
- delivery rate if glucose and FFAs
Inside cell:
- rate of fuel oxidation
- availability of fuel
- enzyme activity
pH
Normal- 7.4
Acidosis- <7.35
Alkalosis- >7.45
Acid
- molecule that can liberate H
- increases H concentration in solution
- lactic acid is a strong acid
Base
- Molecule that is capable of combining with H
- decreases H concentration in a solution
- more readily this molecule combines with H, the stronger the base
- bicarbonate is a strong base
Ion
- molecule missing an electron
- molecule that has gained an electron
Positive effect of pH decrement
- increased O2 delivery, via Bohr effect
- increased muscle blood flow due to local vasodilation
Negative effect of pH decrement
- inhibition of glycolysis and lypolysis
- increased water content of muscle
- decreased lactate efflux from muscle
- increased requirement of ca2
- decrease myosin atp-ase activity
- increased protein binding of ca2 in sarcoplasmic reticulum
- increased of k in the extracellular space
-
What does abnormal pH cause
- inhibit ATP production (slows glycolysis l-inhibit pfk
- interfere with muscle contractile process. Compete with calcium ions at binding sites on troponin
- abnormal activity of the heart/rhythm disturbances (functions of organs)
- enzyme function (denature)
