A.2.3 Energy Systems

Adapted from class notes.

Energy Systems - Introduction

• Macronutrients help determine the amount of energy available

• Carbs and lipids can be stored and are metabolized more slowly

• Proteins are not stores, so they are metabolized quickly

  • Proteins, then carbs, then fats

  • Metabolized meaning broken into monomers to enter the blood

• Nutrients in food not digested are excreted as faeces

• Not all the energy in food is release during metabolism, e.g. urea and ammonia

Metabolism

• Metabolism refers to all the reactions in the body that maintain life

  • Anabolism:

    • Reactions that build up

    • Consumes (or stores) energy

    • Excess glucose can be stores as glycogen

  • Catabolism:

    • Reactions that break down

    • Releases energy

    • Glucose metabolizing to produce carbon dioxide

• Food > Catabolism (releases energy) ~~> Anabolism (requires energy)

Mitochondria

• Mitochondria are organelles present in eukaryotes (including animals, humans)

• Found in high concentration/number in muscle cells

• Produce most (not all) of the cells energy

• REQUIRES oxygen

• This is where the Krebs cycle and electron transport chain take place

ATP

• ATP, Adenosine Triphosphate

• This is the cells energy carrying molecule, cellualr energy “currency”

• Cell respiration - the controlled release of energy in the form of ATP through catabolism or organic molecules

• When ATP is used, the third phosphate (P) group is broken off, and results in the net release of energy for use (such as during muscle contraction)

• Phosphorylation is the process of adding a phosphate (ADP to ATP)

Muscle Contraction

• The contractile force for muscle contractions requires ATP energy

• Muscle cells use macronutrients to produce ATP

• Muscles have enough ATP at any time to do about 2 seconds of work; longer than that needs some energy production through the energy systems

Carbohydrate Metabolism

• Dietary carbs are first broken down into glucose, fructose, and galactose. Fructose and galactose are converted into glucose in the liver

• Glucose is transported via blood to muscles (and other organs)

Reaction Summaries

• Glycolysis: The breakdown of glucose into pyruvate

• Glycogenesis: The use of glucose to make glycogen (when more glucose is eaten/present than is required)

• Gluconeogenesis: The production of glucose from lactate

• Glycogenolysis: The breakdown of glycogen into glucose (when there isn’t enough glucose in blood/muscle)

• Lipolysis: The breakdown of triglycerides into glycerol and 3 fatty acids

• Beta Oxidation: The breakdown of fatty acids from the methyl and into acetyl-CoA

Glycolysis (Glycolytic)

• This happens in the cytoplasm of the cell (outside mitochondria)

• This si the first stop in glucose breakdown

• Splits glucose (C6H12O6) into 2 pyruvate (C3H9O6) molecules

• Also makes 2 ATP!

• Also converts NAD into NADH (which is used later)

Glycolysis - Lactate

• If there is not enough oxygen present, an additional step of converting pyruvate into lactate (lactic acid) occurs

• Anaerobic

• This converts NADH back into NAD

• The NAD allows glycolysis to continue

• No additional energy is made converting pyruvate to lactate!

Aerobic (Oxidative) - Glucose

• If oxygen is present, pyruvate does not turn into lactate

• Pyruvate is converted into Acetyl-CoA (2 carbon atoms, so 1 CO2 is released here)

• Each 1 glucose molecule generates 2 Acetyl-CoA molecules

• Acetyl-CoA enters the Krebs Cycle

Aerobic (Oxidative) - Fatty Acids

• If oxygen is present, and exercise intensity is faily low

• Fatty acids have two carbon atoms from the end of the chain removed to generate a molecule of Acetyl-CoA

• Fatty acids are variable length. 1 Acetyl-CoA are made for every two atoms of C in the fatty acid

• Saturated fats are harder to metabolize

Aerobic (Oxidative) - Krebs Cycle

• Acetyl-CoA feeds in to the Krebs cycle

• Krebs ONLY HAPPENS IF THERE IS OXYGEN!!!!!

• Oxygen is not a part of Krebs

• Krebs generates NADH, which is a reactant of the electron transport chain

• Krebs is where the majority of CO2 is made (2CO2 for energy Acetyl-CoA)

• Makes small amount of ATP (1 per Acetyl-CoA)

• Happens in the mitochondria matrix

Aerobic (Oxidative) - ETC (Electron Transport Chain)

• The electron transport chain is the largest producer of ATP

• Requires oxygen as a reactant

• Also uses NADH/FADH2 as electron carriers

• For every molecule of glucose, ~34 ATP made

Anaerobic - Phosphagen (Creatine Phosphate)

• Creatine phosphate (PCr) is an energy storage molecule

• During rest, ATP shifts a phosphate to creatine. This generates PCr and ADP

• During periods of maximal intensity exercise and early exercise, PCr rapidly regenerates ATP

• PCr is more stable than ATP, so can exist for a longer period of time than ATP

• Up to 20 seconds of all-out (maximal) effort

• Depletion of PCr means another energy system has to take over to continue exercise

Summary: Phosphogen

1. Aerobic or Anaerobic

2. Reactant(s)

3. Product(s)

4. Location

5. ATP: Reactant Ratio

6. ATP Per Glucose

7. Use

8. Other

1. Anaerobic

2. Creatine Phosphate

3. Creatine

4. Cytoplasm

5. 1:1

6. N/A

7. maximal effort

8. Fastest producer of ATP; first to run out. Up to 205

Summary: Glycolysis

1. Aerobic or Anaerobic

2. Reactant(s)

3. Product(s)

4. Location

5. ATP: Reactant Ratio

6. ATP Per Glucose

7. Use

8. Other

1. Anaerobic

2. Glucose and NAD

3. Pyruvate and NADH

4. Cytoplasm

5. 2:1

6. 2

7. High intensity

8. fast producer of ATP; produces NADH for ETC

Summary: Lactate

1. Aerobic or Anaerobic

2. Reactant(s)

3. Product(s)

4. Location

5. ATP: Reactant Ratio

6. ATP Per Glucose

7. Use

8. Other

1. Anaerobic

2. Pyruvate and NADH

3. Lactate and NAD

4. Cytoplasm

5. 0

6. 0

7. High intensity

8. Follows glycolysis if no O2, allows glycolysis to continue. Can only sustain for about a minute

Summary: Beta Oxidation

1. Aerobic or Anaerobic

2. Reactant(s)

3. Product(s)

4. Location

5. ATP: Reactant Ratio

6. ATP Per Glucose

7. Use

8. Other

1. Aerobic

2. Fatty acids

3. Acetyl-CoA

4. Mitochondira

5. o

6. N/A

7. Low-moderate intensity

8. Fats carry lots of energy, large sotrage, difficult to deplete

Summary: Krebs

1. Aerobic or Anaerobic

2. Reactant(s)

3. Product(s)

4. Location

5. ATP: Reactant Ratio

6. ATP Per Glucose

7. Use

8. Other

1. Aerobic

2. Acetyl-CoA (from glycolysis or Beta Oxidation)

3. CO2 and NADH

4. Mitochondrial matrix

5. 1:1

6. 2

7. Low-moderate intensity

8. Only runs if O2, ETC uses products

Summary: ETC

1. Aerobic or Anaerobic

2. Reactant(s)

3. Product(s)

4. Location

5. ATP: Reactant Ratio

6. ATP Per Glucose

7. Use

8. Other

1. Aerobic

2. O2 and NADH

3. H2O and NAD

4. Mitchondrial invermembrane

5. ~6:1

6. 36

7. Low-moderate intensity

8. Uses up products of Krebs and glycolysis

Aerobic vs. Anaerbic Intensity

• Aerobic is main energy systems at low and rest intensity

• As intensity increases, fats stop being used first

• Anaerobic takes over more as intensity increases to high/maximal

• Phosphogen is main energy source in maximal

• No fatty acids above 90% effort

Hormonal Regulation - Insulin

• Eating leads to rise in blood sugar

• High blood sugar causes pancreas to release insulin

• Insulin helps to transport sugar into cells (nucleic and liver)

  • Insulin causes GLUT4 to transport glucose into cell

• Stimulates: Glycogenesis, glycolysis

• Inhibits: Glyconeogenesis, glycogenolysis, lipolysis

Hormone Regulation - Glucagon

• When blood sigar is low (fasting or after exercise), pancreas secretes glucagon

• Glucagon works like the opposite of insulin

• Stimulates: Glycogenolysis (makes glucose), lipolysis, epinephrine release

• Epinephrine (during exercise) works similarly to glucagon. Glucagon mainly works on liver, epinephrine on muscles

Hormone Regulation - Exercise

• During exercise, muscle contraction carries GLUT4 to let glucose into cell without the need for insulin

• Exercise lowers insulin concentration, can also increase insulin sensitivity

Maximal Oxygen Consumption (VO2max)

• VO2max is the maximum rate O2 is taken in and used

• High VO2max = high cardiovascular function

Absolute and Relative VO2max

• Absolute = Liters O2 per minute

• Relative = mL per minute per kg

• Relative is more important when the person’s weight matters (e.g. if they have to move themselves)

• Lighter body weight translates to higher relative VO2 max

• Males typically are higher relative VO2max than female

• Highestn found in cross country skiers at around 90mLkg-1min-1

• Untrained health is 40-45 (male) or 35-40 (female)

• Higher relative means being able to run faster for longer

• Contributing factors to difference between males and females:

  • Cardiac output (smaller heart size in females)

  • Blood volume

  • Haemoglobin concentration

  • Lung capacity

  • Body composition (males have lower body fat on average)

• VO2max decreases with age (about 1% per year)

Training and VO2max

• Central adapatations (of the cardiovascular system)

  • Stroke volume increases with training

  • Left ventricles hypertrophy

• Peripheral adaptations (of the muscle)

  • Increased capillary density

  • Increased ability for muscles to capture oxygen

• More muscle use activities induces high trained VO2max (cross country skiing > running > cycling)

• Running Economy (RE) - the VO2 at a given running velocity

  • good RE use less O2 at a given speed