Cellular Energy Production Quiz

Cellular Energy Production

• ATP is the cell's energy currency, formed from food's potential energy and used to power cellular work. ATP consists of adenosine and three phosphate groups.
• Hydrolysis of one ATP molecule releases 7.3 kcal/mol of energy.
• The body stores approximately 80-100g of ATP near contractile proteins, enough for several seconds of maximal exertion.
• Muscles regenerate ATP via three metabolic pathways:
  • Phosphagen system: Fastest, regenerates ATP from creatine phosphate or two ADP molecules. This process doesn't require oxygen and the body stores 3-4 times more creatine phosphate than ATP.
  • Glycolysis: Utilizes blood glucose or muscle glycogen to produce ATP. Carbohydrates are the only anaerobic fuel source. Pyruvate, if oxygen is not available, converts to lactate, causing an increase in muscle/blood acidity.
  • Cellular oxidation: Uses oxygen in the mitochondria to generate ATP from various nutrients.

Carbohydrate Energy Release

• Anaerobic conditions: Glucose + 2ADP + 2Pi → 2 lactate + 2ATP + 2H₂O+2NAD+
• Aerobic conditions: Glucose + 2ADP + 2Pi ↔ 2 pyruvate + 2ATP + 2H₂O + 2NADH
• Complete oxidation of one mole of carbohydrate yields 32 ATP molecules.

Fat Metabolism

• Body's most abundant energy source, stored as triglycerides. Fat breakdown sources include stored triglycerides, circulating triglycerides, and adipose tissue.
• Triglycerides, with 16 or 18 carbon chains, are broken down into acetyl groups primarily via beta oxidation.
• Different fatty acids yield different amounts of ATP. Stearic acid (18C) yields 147 ATP and palmitic acid (16C) yields 129 ATP, but requires 23 moles of oxygen. Fat catabolism can be relied upon during sufficient oxygen availability.

Protein as Energy

• Proteins can serve as energy substrates, especially during long-duration endurance activities.

Energy Spectrum of Exercise

• The contribution of different energy systems varies based on exercise intensity and duration; moving smoothly from one source to another as exercise progresses.
• Aerobic energy is prominent for low-intensity movement, using fat as the primary fuel source. High intensity exercise increases the liver's glucose release to muscles.

Immediate Energy (ATP-PCr System)

• Used for activities lasting less than 3 minutes. Explosive activities (5-10s) rely on this system. Lactate is not accumulated.

Short-Term Energy (Rapid Glycolysis)

• Activities lasting longer than 15 seconds increasingly rely on glycolysis. Insufficient oxygen during initial 2-3 minutes of exercise leads to pyruvate converting to lactate.
• Lactate accumulates when exercise intensity is more than 55% of aerobic metabolism capacity. (70-80% for endurance athletes) meaning oxygen demand exceeds oxygen supply.

Long-Term Energy (Aerobic System)

• Oxygen uptake during exercise reaches a steady state when energy required matches aerobic ATP production.
• Oxygen deficit occurs when exercise starts at the onset, with a difference between VO2 uptake during exercise, and the total that would have been consumed if a steady state was achieved. Untrained individuals take longer to reach steady state.

Prolonged Exercise

• Muscle glycogen depletion occurs more rapidly with higher exercise intensity.
• Exercise duration increase leads to carbohydrate depletion, emphasizing fat as an energy source, reducing work rate, and possibly oxygen being unable to oxidize fats.

Recovery VO2

• Reflects oxygen deficit and is related to exercise intensity. Low-intensity exercise requires less recovery and minimal lactate accumulation; moderate-to-heavy exercise requires longer recovery.
• Recovery VO2 is used to restore energy stores, use substrates, restore hormone and temperature balance, repair damaged tissues, and synthesize proteins.

Fate of Lactic Acid

• Accumulated lactate is processed during recovery by conversion to pyruvate, gluconeogenesis (and Cori cycle), conversion to amino acids and through excretion in sweat and urine.

Calorimetry & Respiratory Quotient

• Calorimetry measures heat release through metabolism and assesses the aerobic system. Indirect measurements, like oxygen uptake, are also used.
• Respiratory quotient (RQ) or Respiratory Exchange Ratio (RER) = VCO2/VO2, used to calculate energy expenditure.

Maximal Oxygen Uptake (VO2 Max)

• The maximum rate of oxygen consumption during exercise, assessing maximal aerobic ATP production.
• VO2 max is measured during volitional fatigue, providing a standard for comparing performance in various populations. VO2 max is typically lower in women, and influenced by heredity, training, age, and body composition.
• Limiting factors vary between healthy individuals and those with lung, heart or neurological conditions.

Effects of Regular and Inactivity on Energy metabolism

• Physical activity increases the body's capacity for energy production, maintaining or regaining independence. Lack of activity negatively impacts substrate storage, enzyme activity, and ability to perform tasks.

Energy Cost of Activity

• MET (metabolic equivalent) measures resting oxygen consumption. Sedentary (<3 METs), Light-moderate (3-6 METs), and Vigorous (>7 METs) are various intensity levels.

Steps for Activity

• Recommendations for daily step counts to achieve health benefits: Sedentary (< 5,000 steps/day), Goal (7,500 steps/day).

Effects of Physical Activity on Anaerobic Energy Sources

• Overload the metabolic pathways, increasing capacity. This includes immediate sources (high-intensity interval training) and anaerobic sources (high-intensity interval training).
• Training central and peripheral systems, such as increasing muscle glycogen and aerobic enzyme activities is a positive impact of physical activity.