energestics and anaerobic metabolism

Question 1

energetics

Answer 1

life depends on energy transfer according to 1st and 2nd laws of thermodynamics
potential energy in macronutrients is transferred to kinetic energy
chemical reactions involving energy transfer will result in energy loss, heat liberation and free energy (2nd law0
- ΔG=ΔH–TΔS
- G is negative when free energy contents of products is less than reactants

Question 2

issues with energy systems graph

Answer 2

overestimates glycolytic contributuin
underestimates aerobic contribution
no-linear time scale so does nt reflect reality
Y axis (capacity) is meaningless
bioenergetics doesnt work like that

Question 3

ATP

Answer 3

molecule that transfers energy is ATP by hydrolysis to ADP and inorganic phosphate - free energy released
conc of ATP in muscles (~5mmol/kg-1) enough for a few seconds of maximal activity
more than twice the molar mass of glucose of PC
all other energy systems are used to resynthesise ATP

Question 4

ATP hydrolysis

Answer 4

catalysed by ATPase
myosine ATPase at crossbridges
membrane bound ATPase at NaK+ pump (pumps are atpase)
products= ADP,pi and proton
G of atp hydrolysis = 31kj/mol
free energy powers all cellular work

Question 5

ATP resynthesis

Answer 5

muscle atp conc doesnt change significantly except under high conditions of high intensity exercise ]
resynthesis of ATP is a phosphorylation process- must use metabolites to reverse hydrolysis
substrate level phosphorylation - pcr hydrolysis + glycolytic atp production
oxidtaive phosphorylation- substrate level phosphorylation inside mitochondria with o2 as final H+ and electron acceptor

Question 6

Lohmann reaction

Answer 6

second component of the ATP:PCr system
creatine kinase hydrolysis of PCr to Cr and PI, free energy used to resynthesise ATP from ADP and Pi (G=43kj/mol)
near equilibrium reaction prevents in ATP concentration
pcr will break down at some point - is finite

Question 7

adenylate kinase

Answer 7

during high intensity exercise or low energy availibity, ATP can decrease, ADP increases and this can be hydrolysed to aMP
ADP + ADP <–> ATP +AMP
cataluysed by adenylate kinase- myokinase
no net change in free energy
conc of AMP is usually low and only rised when energy supply is compromised
easily sensed b y AMP activated protein kinase (AMPK), key regulator of protein synthesis to endurance exercise

Question 8

AMP deamination

Answer 8

accumalation of AMP produces unfavourable conditions for adenlyate kinase reaction
amp accumalation prevented deamination to IMP and ammonia
AMP + h20–> IMP + NH4 (catalysed by AMP deaminase)
helps to maintain a high ratio between atp and adp - loss of some adenine nucleotides in short term maintains high rates of atp turnover
occurs towards end of high intensity exercise

Question 9

metabolite changes during sprint exercise

Answer 9

usually force, power or speed are used to infer energy transfer
direct measurement of ATP, PCr +Pi all possible but are invasice and expensive

muscle biopsy and direct measurement of metabolites using validated assays can measure single fibre metabolite concentration, only representative of sample , not whole muscle- small sampling freq

Question 10

magnetic resonance spectroscopy

Answer 10

measures relative abundance of phosphorus metabolites in relatively large muscle volume, high sampling freq, limited of exercise that can be performed in the bore of the magent- probne or supine position (lying on front or back)

pcr- after 30s sprint reduces greately, atp dropped slightly, adp stayed similar
pcr goes down a lot to counteract the reduction of atp

Question 11

phosphorylation potential

Answer 11

atp rarely falls during exercise despite energy demand changing by as miuch as 100 fold
balance between atp hydrolysis and atp resynthesis must be tightly regulated - meet energy demands without wasting energy stores
potential= (adp)(pi)/(atp)
indicated relative balance between atp and direct products of its hydrolysis - any rise would require increased atp resynthesis

Question 12

cellular energy change

Answer 12

([ATP] + 0.5[ADP])/([ATP] + [ADP] + [AMP])

indicates how much of the adenine nucleotide pool isn phosphorylated - adp and amp are key metabolic regulators
elevated adp, amp and ca2+ avtucate glycolytic enzymes, producing atp through glycolysis

Question 13

glycolysis

Answer 13

substrate level phosphorylation from glucose and glycogen
may be called anaerobic glycolysis or anerobiosis
ancient means of generating atp from glucose/ glycogen found in all eukaryotic life
glycolysis involves 10 reaction steps ultimately producing pyruvate or lactate and 2 atp molecules
reactions are slow compared to lohmann reaction but 20x faster than phosp
immeduate energy transfer

Question 14

investment phase

Answer 14

investing free energy to use free energy later
glucose must be converted glucose 6 phosphate or converted to glycogen to keep cell glucose low
glucose 6 phopshate unable to leave cell
converstion of fructose 6 phopshate to fructose 1,6 phhophaspete catlysed by PFK, consuming ATP
irreversible, rate limiting step
numbers refer to carbon atom the phosphate is bonded to

Question 15

ayoff

payoff phase

Answer 15

adolase catobolises fcutose 1,6 biphosphate to glyceraldehyde 3 phopshate
here- 6 carbon molecules have split into 2- all downstream occur twice for every glucsoe molecule metabolised
reduction of NAD to nadh ,. priducing 2 atp
pyruvate kinase catalysed final resulting in pyruvate
pyruvate must be oxidised or coverted to lacate at this poiny to maintain nad+ supply
net production of 2 atp from glycolysis

Question 16

lactate

Answer 16

• lactate /= lactic acid- lactic acid does not appear in the body
• lactate ion accompanies by a proton for charge balance lowers compartment pH (increase lactate decrease pH)
• lactate is present in the muscle at rest so notion that it is only produced when o2 is lacking is wrong
• lactate concentration is not lactate production- reflects balance between production and oxidation

Question 17

measurement of lactate

Answer 17

fingertip blood sampling
lactate + o2–> pyrivate + h2o2
can measure lactate by looking at oxcygen depletion or hydrogen peroxide production

Question 18

interpreting blodo lactate

Answer 18

• arterial, venous or capillary sampling possible; latter most common
• blood lactate is also not a measure of lactate production
• typical resting value0 1-2mM
• peak value after prolonged sprint 10-20mM
• two LDH isoforms (LDH-M + LDH-H)- M= type 2 fibres , H= type 1 fibres
• monocarboxylate transporters (MCTs) are responsible for lactate release and uptake

Question 19

why does glycolotic rate slow down

Answer 19

• Reduced glycolytic rate
• PFK is the rate limiting step in glycolysis – highly pH sensitive
• ATP is a substrate for and an inhibitor of PFK
• High conc of ATP results in binding to an allosteric inhibitory site
• Probability of binding increased at low pH (eg metabolic lactic acidosis)
• Also reduced affinity for fructose 6-phosphate, slowing reaction rate
• Slows lactate (and H+) production but also reduces muscle power