Energy Systems 1

Question 1

What do the 1st and 2nd laws of thermodynamics state in relation to energetics?

Answer 1

• Energy cannot be created or destroyed (1st law)
• Energy transfer increases entropy (2nd law)

Question 2

How is potential energy from macronutrients used in the body?

Answer 2

It is transferred to kinetic energy for muscle activity, ion pumping etc

Question 3

What does the Gibbs free energy equation represent?

Answer 3

ΔG = ΔH – TΔS, showing the free energy available after accounting for entropy and heat

• T is the absolute temp (310 Kelvin)

Question 4

What does a negative ΔG value indicate?

Answer 4

That the products have less free energy than the reactants

• so energy is released in the reaction
• therefore reaction can occur naturally

Question 5

What is ATP and why is it important?

Answer 5

ATP is the primary energy transfer molecule in the body, used to fuel cellular work

Question 6

Why can’t the body store large amounts of ATP?

Answer 6

Because ATP has a high molar mass, making it heavy and energetically costly to store

• more than twice molar mass of glucose + PCr

Question 7

What processes are used to resynthesise ATP?

Answer 7

• PCr hydrolysis
• Glycolysis
• Oxidative phosphorylation of CHO, fat, protein and alcohol

Question 8

What enzyme catalyses ATP hydrolysis?

Answer 8

ATPase including…

1. Myosin ATPase at cross-bridges
2. Membrane-bound ATPases at ion pumps

Question 9

What are the products of ATP hydrolysis?

Answer 9

ADP, Pi and a proton

Question 10

What is the free energy change (ΔG) of ATP hydrolysis?

Answer 10

-31 kJ/mol

• remember negative means no energy input is required - it happens spontaneously
• ignore the negative though as it suggests a direction of energy transfer

Question 11

When does ATP concentration in muscle significantly fall?

Answer 11

Only during exhaustive high-intensity exercise

Question 12

Why is ATP concentration tightly regulated?

Answer 12

Because low ATP levels lead to breakdown of essential cellular functions

Question 13

What are the two main types of ATP resynthesis?

Answer 13

• Substrate-level phosphorylation (PCr hydrolysis + glycotic ATP production)
• Oxidative phosphorylation (O2 as final proton electron acceptor)

Question 14

What is a more accurate term for ‘anaerobic glycolysis’?

Answer 14

Glycolysis

Question 15

What is the Lohmann reaction apart of?

Answer 15

The second component of the ATP-PCr system

Question 16

What enzyme catalyses the Lohmann reaction?

Answer 16

Creatine kinase

Question 17

What reactions does creatine kinase catalyse in the ATP:PCr system?

Answer 17

Catalyses the hydrolyses of PCr → Cr + Pi

• free energy is then used to resynthesise ATP from ADP + Pi

Question 18

What is the ΔG of the PCr reaction in the Lohmann reaction?

Answer 18

-43 kJ/mol

Question 19

Why is the PCr reaction crucial during intense exercise?

Answer 19

It helps maintain ATP levels by resynthesising ATP rapidly

Question 20

What happens to ADP levels during high-intensity exercise or low energy availability?

Answer 20

ADP levels increase, which can lead to AMP formation

• ADP is hydrolysed to AMP

Question 21

What is the reaction catalysed by adenylate kinase (myokinase)?

Answer 21

ADP + ADP ↔ ATP + AMP

Question 22

What is the net energy change of the adenylate kinase reaction?

Answer 22

No net change in free energy

Question 23

What signals low energy availability in the cell to AMPK?

Answer 23

Increased AMP concentration

• usually very low so when it rises it shows energy supply is compromised

Question 24

What is AMPK and its role during exercise?

Answer 24

AMP-activated protein kinase

• it regulates protein synthesis in response to endurance exercise

Question 25

Why is AMP deaminated during intense exercise?

Answer 25

To prevent AMP accumulation and maintain ATP:ADP ratio - AMP produces unfavourable conditions for adenylate kinase reaction

Question 26

What is the reaction catalysed by AMP deaminase?

Answer 26

AMP + H₂O → IMP + NH₄⁺ - inosine monophosphate + ammonia

Question 27

When and why does AMP deamination typically occur?

Answer 27

Toward the end of high-intensity exercise - done to maintain a high ratio between ATP and ADP

Question 28

What is usually used to infer energy transfer during sprint exercise?

Answer 28

Force, power or speed

Question 29

Why is direct measurement of ATP, PCr and Pi challenging?

Answer 29

It is invasive + expensive - these metabolites are confined to muscle cells

Question 30

What method allows direct measurement of muscle metabolites with validated assays?

Answer 30

Muscle biopsy

Question 31

What is a limitation of the muscle biopsy method?

Answer 31

Low frequency of sampling and limited representativeness

Question 32

What method measures phosphorus metabolites in muscle non-invasively?

Answer 32

Magnetic Resonance Spectroscopy (MRS)

Question 33

How does Magnetic Resonance Spectroscopy work?

Answer 33

Similar to an MRI but its tuned for phosphorus-31 instead of hydrogen

Question 34

What is an advantage of MRS in exercise studies?

Answer 34

High sampling frequency (spectra every 5 seconds)

Question 35

What is a limitation of MRS for exercise testing?

Answer 35

Limited to exercises that can be done prone or supine inside the magnet bore

Question 36

What did Cheetham et al. (1986) study involve?

Answer 36

30 sec treadmill sprints with muscle biopsy samples frozen within 7–8 seconds post-exercise

Question 37

What did Cheetham et al. (1986) find + how did it compare to energy system data from the 1970s?

Answer 37

Evidence of sig. metabolic stress but not evidence of time of course changes - so much of it was largely guesswork due to lack of real-time data

Question 38

What is the desired ratio between ATP and ADP in muscle?

Answer 38

A high ATP:ADP ratio

Question 39

What happens to PCr and Pi levels after 5 minutes of maximal contractions, according to MRS data?

Answer 39

PCr decreases significantly and Pi increases massively

Question 40

What is the shift in Pi during exercise directly correlated with?

Answer 40

pH changes

Question 41

Why does ATP concentration rarely fall during exercise?

Answer 41

Because ATP hydrolysis and resynthesis are tightly regulated to meet energy demands without wasting stores

Question 42

What does phosphorylation potential indicate?

Answer 42

The balance between ATP and the products of its hydrolysis - any rise would require increased ATP resynthesis

Question 43

What does cellular energy charge reflect?

Answer 43

How much of the adenine nucleotide pool is phosphorylated

Question 44

What stimulates ATP resynthesis in response to energy charge?

Answer 44

Decreases in cellular energy charge (mainly through rising ADP and AMP)

Question 45

Which molecules activate glycolytic enzymes during high energy demand?

Answer 45

ADP, AMP, and Ca²⁺ = producing ATP via glycolysis

Question 46

What is glycolysis also known as?

Answer 46

The Embden–Meyerhof–Parnas pathway

Question 47

Why is the term “anaerobic glycolysis” misleading?

Answer 47

Because glycolysis can occur with or without oxygen

Question 48

What is the end product of glycolysis?

Answer 48

Pyruvate (or lactate) + ATP

Question 49

How many ATP are produced by glycolysis?

Answer 49

Net gain of 2 or 3 ATP per glucose molecule

Question 50

How fast is glycolysis compared to oxidative phosphorylation and Lohmann Reaction?

Answer 50

- ~20 times faster than oxidative phosphorylation - Slow compared to Lohmann Reaction

Question 51

What must happen to glucose before entering glycolysis + why?

Answer 51

It must be converted to glucose 6-phosphate - because glucose-6-phosphate cannot leave the cell

Question 52

Where does most glycolytic energy come from?

Answer 52

Glycogen hydrolysis (not glucose) - glycogen is usually how its stored

Question 53

What enzyme catalyzes the conversion of fructose 6-phosphate to fructose 1,6-biphosphate?

Answer 53

Phosphofructokinase (PFK) - F-6-P from G-6-P previously mentioned

Question 54

How many ATP are consumed in the investment phase + at which stage?

Answer 54

2 ATP - 1 ATP for glucose -> glucose-6-phosphate 1 ATP for Fructose-6-phosphate to fructose-1,6-phosphate

Question 55

Why is PFK a key enzyme in glycolysis?

Answer 55

It catalyses an irreversible, rate-limiting step

Question 56

What enzyme splits fructose 1,6-biphosphate into two 3-carbon molecules?

Answer 56

Aldolase

Question 57

What are the two products of aldolase activity?

Answer 57

1. Glyceraldehyde 3-phosphate 2. Dihydroxyacetone phosphate (DHAP)

Question 58

How is DHAP handled in glycolysis?

Answer 58

It is converted to glyceraldehyde 3-phosphate by triose phosphate isomerase - highly active enzyme so happens almost immediately

Question 59

How many times do downstream reactions of glycolysis occur per glucose molecule?

Answer 59

Twice (due to 6-carbon molecules splitting into two 3-carbon molecules)

Question 60

What is the final enzyme in glycolysis and its product?

Answer 60

Pyruvate kinase = produces pyruvate

Question 61

In this downstream reaction, how many ATPs are made?

Answer 61

2 ATP and reduction of NAD+ to NADH - but as the reactions occur twice - times this number by 2 (so 4 ATP)

Question 62

Why must pyruvate be oxidised after glycolysis / converted to lactate?

Answer 62

To maintain NAD+ supply

Question 63

Why is only 1 ATP consumed when starting from glycogen rather than glucose?

Answer 63

Glycogen is converted directly to glucose 6-phosphate, bypassing the need for ATP at the first step (glucose -> glucose-6-phosphate) - hence why net ATP can be 2 or 3 in glycolysis

Question 64

What is the state of lactic acid at physiological pH (pKa ~3.9)?

Answer 64

Fully dissociated into lactate ion (La⁻) and a proton (H⁺) for charge balance

Question 65

What effect does lactate production have on compartment pH?

Answer 65

Lowers pH due to accumulation of H⁺ ions (metabolic acidosis)

Question 66

Is lactate only present during exercise or O₂-limitation?

Answer 66

No, lactate is present even at rest - lactate production is not solely due to lack of O₂

Question 67

What determines lactate concentration in the body?

Answer 67

The balance between lactate production and clearance (for oxidation)

Question 68

What is the principle behind lactate measurement using H₂O₂?

Answer 68

Lactate + O₂ → pyruvate + H₂O₂ - H₂O₂ (hydrogen peroxide) is quantified to estimate lactate concentration as a faster method

Question 69

What are typical resting and peak blood lactate concentrations?

Answer 69

- Resting = 1–2 mM - Peak (after sprint) = 10–20 mM

Question 70

Why isn’t blood lactate a direct measure of lactate production?

Answer 70

Because it reflects both production and oxidation/clearance rates

Question 71

What types of blood sampling are used for lactate?

Answer 71

Arterial, venous, and capillary (capillary most common)

Question 72

What are the two lactate dehydrogenase (LDH) isoforms and their functions?

Answer 72

1. LDH-M (muscle): Found in type II fibres, favours lactate production from pyruvate 2. LDH-H (heart): Found in type I fibres, favours lactate consumption (lactate -> pyruvate)

Question 73

What transports lactate across membranes?

Answer 73

Monocarboxylate transporters (MCTs)

Question 74

How did Gaitanos et al. (1993) estimate anaerobic ATP production?

Answer 74

Using 10 × 6 sec sprints + changes in PCr, lactate, and pyruvate

Question 75

What enzyme limits the rate of glycolysis and is pH-sensitive?

Answer 75

Phosphofructokinase (PFK)

Question 76

How does ATP affect PFK activity?

Answer 76

Acts as both a substrate and an allosteric inhibitor

Question 77

How does low pH affect PFK and glycolysis?

Answer 77

- Increases ATP binding to inhibitory site on PFK - Reduces PFK's affinity for fructose 6-phosphate - Slows glycolysis and lactate (+H⁺) production, but reduces muscle power