Putting molecules together to make bigger molecules.

amino acids-------proteins

glucose-------glycogen

1 kilocalorie is the amount of heat energy needed to raise 1 kg of water 1 degree C at 15 degrees C.

1 Calorie (kcal) = 4.18 Joules (J)

3,000-7,000 kcals= ~12-30 MJ

*Carbohydrate (glucose and glycogen)

*Fat (triglycerides)

*Protein (amino acids)

*Readily availalbe (if included in diet) and easily metabolized by muscles

*Ingested, then taken up by muscles and liver and converted to glycogen

*Glycogen stored in the liver is converted back to glucose as needed and transported by the blood to the muscles to form ATP

Typical Glycogen Values

*Normally fed, Untrained Individual--55-85 mmol/kg

*Normally Fed, Trained Individual-- 110-135 mmol/kg

*Trained, well Rested Individual-- 180 mmol/kg

*Trained, Carbohydrate Loaded-- 220-240 mmol/kg

*Glycogen has a high energy yield per liter of O2 uptake (~5.1 kcal/L O2)

*Glycogen can be metabolized both aerobically and anaerobically

*Rapid activation of the metabolic pathways for glycogen metabolism

*Glycogen concentration can be greatly increased by training and diet

*Glycogen can be the sole source of energy during heavy exercise

*Glycogen is stored with large amount of H20, thus reducing the caloric value of the storage form (1.1 kcal/g glycogen)

*The total amount of glycogen that can be stored is relatively small

*Anaerobic use of glycogen results in the accumulation of lactate (and thus pH), which may interfere with a number of cellular processes

*Muscle cells are dependent upon their internal glycogen stores; when these stores are depleted, moderately heavy exercise cannot continue

*Provides substantial energy during prolonged, low-intensity activity

*Body stores of fat are larger than carbohydrate reserves (considerably larger)

*"Less accessible" for metabolism because it must be reduced to glycerol and free fatty acids (FFA)

*Only FFAs are used to form ATP

*General formula: CH3(CH2)nCOOH

*Most fatty acids that are important for human energy metabolism during exercise have 12-18 total carbons

Intramuscular Triglycerides

100-240 mmol/kg

*Fat has the highest energy value of any fuel (9.3 kcal/g)

*Fat can be stored in large amounts in various tissues throughout the body

*Fat is a stable energy source, yet it can be mobilized for use during exercise

*Compared to glycogen, the total caloric value of intramuscular fiber lipid is small

*Energy release from fat only occurs with the uptake of oxygen

*The oxidation of fat yields less energy per liter of oxygen consumed (4.62 kcal/L) than does CHO

*Since the majority of fat is stored outside the muscle and are not water soluble, there is delayed transport of FFA's to the muscle

*Fats cannot serve as the sole energy source of energy

*Can be used as energy source if converted to glucose via glucogenesis (in liver)

*Can generate FFA's in times of starvation through lipogenesis

*Only basic units of protein--amino acids-- can be used for energy

*Approximately 20% of human body is protein (14 kg of a 70 kg man)

*Thus, ~234 MJ (52,000 kcals) of potential energy is stored in the form of protein

*Each grom of CHO yields 17 kilojoules (~kcals)

*Each gram of FAT yields 37 kilojoules (~9 kcals)

*FAT is stored neatly (compactly) within lipid droplets

*For every 1 g of glycogen, 2.7 g of H2O are stored

*Caloric value of storage form is equivalent to ~1.1kcal/g glycogen (energy to wet weight ratio)

*Liver glycogen- 100 grams

*Adipose Tissue- Tryglyceride 12 kg

*Blood and extracellular glucose- 20 grams

*Muscle (glycogen)- 500 grams

*Muscle triglyceride- 300 grams

**These amounts are those typically stored by a 70-75 kilogram athlete.

*Carbohydrates

**Liver glycogen- 110 grams, 451 kcal

**Muscle glycogen- 250 grams, 1025 kcal

**Glucose in body fluids- 15 gram, 62 kcal

***Total- 375 grams, 1538 kcal

*Fat

**Subcutaneous- 7800 grams, 70980 kcal

**Intramuscular- 161 grams, 1465 kcal

***Total- 7961 grams, 72445 kcal

(These estimates are based on an average body weight of 65 kb (143 lb) with 12% body fat)

Carbohydrate

*Muscle: 500g - 8.4 MJ - 2000 kcals

*Liver: 100 g- 1.7 MJ - 400 kcals

*Total= ~10 MJ of energy

Remember, 1 liter of O2 = ~5 kcals of energy "burned"

So, at 3.0 L/min (~70% VO2max) CHO oxidation would support energy demands for 2-2.5 hours.

Fat:

*Adipose: 8 kg - 300 MJ - 72000 kcals

*Muscle: 200 g - 7.5 MJ - 1800 kcals

**Total = ~308 MJ of energy

(Remember, 1 L of O2 = ~5 kcals of energy "burned")

So, at 3.0 L/min (~70% VO2max) Fat oxidation would support energy demands for ~3.5 days (82 hours)

Protein:

*Total: 14 kg - 234 MJ - 52000 kcals

Total = ~234 MJ of energy

(Remember, 1 L of O2 =~5 kcals of energy "burned")

So, at 3.0 L/min (70% VO2max) PRO oxidation would support energy demands for 2.5 days (62 hours) 

1. ATP-PCr System- quick, explosive energy source

2. Glycolytic System- short, high intensity energy source - anaerobic breakdown of carbohydrates (glucose and glycogen)

3. Oxidative System- long term aerobic energy production (carbohydrate and fat metabolism)

*Glycolysis

*Krebs cycle

*Electron Transport Chain

*Beta-Oxidation (oxidation of fats)

First 30 seconds- Anaerobic-80%     Aerobic-20%

Second 30 seconds- Anaerobic- 60%     Aerobic- 40%

Third 30 seconds- Anaerobic- 42%     Aerobic- 58%

Last 30 seconds- Anaerobic- 33%     Aerobic- 66%

*This system can prevent energy depletion by forming more ATP

*This process is anaerobic

*1 mole of ATP is produced per 1 mole of phoshocreatine (PCr)

*Occurs in the cytosol of the cell

*Provides energy (ATP) for only a few seconds (3-15 seconds) during intense muscular effort

Pcr--->(creatine kinase over the arrow)   Pi+Creatine

ADP to Pi---> ATP

*Requires 10-12 (depending on where the reaction stops) enzymatic reactions to breakdown glucose and glycogen into ATP

*Glycolysis that occurs in glycolytic system is anaerobic 

*Glucose is a 6 carbon structure (C6H12O6)

*Glucose is broken down into two 3-carbon structures called pyruvic acid

*The pyruvic acid is then converted to Lactic acid

*The breakdown of glucose yields 2 ATP

*The breakdown of glycogen yields 3 ATP

*The breakdown of carbohydrates are the only nutrient whose stored energy can be used to generate ATP anaerobically 

Important Steps of Glycolysis 1

Hexokinase

Important Steps of Glycolysis 2

GLycogen Phosphorylase

Important Steps of Glycolysis 3

Phosphofructokinase

Important Steps of Glycolysis 4

Phosphoglycerate Kinase

Important Steps of Glycolysis 5

Pyruvate Kinase

Important Steps of Glycolysis 6

Lactate Dehydrogenase

*A total of 4 ATP are produced, but only a net of 2 ATP can be used for energy production

*Only carbohydrates can be utilized via glycolysis

*Glycolysis "breakdowns" 6-carbon structures (glucose) to 3-carbon structures (lactic acid)

*Relies on oxygen to breakdown fuels for energy

*Produces ATP in mitochondria of cells

*Can yiedl much more energy (ATP) than anaerobic systems

*Is the primary method of energy production during endurance events

1) Oxidation of Carbohydrate

*Glycolysis

*Krebs Cycle

*Electron Transport Chain (ETS)

2) Oxidation of Fat

*Beta-Oxidation

*Krebs Cycle

*Electron Transport Chain

*Glycolysis occurs in the cytosol of the cell

*The Krebs Cycle occurs in the mitochondira of the cell

*In the presence of oxygen pyruvic acid is converted into acetyl coenzyme A (acetyl CoA)

*Acetyl CoA enter Krebs Cycle

2 ATP, 6 NADH, 2 FADH2---> Electron Transport Chain

1 NADH= 3 ATP - Total of 18 ATP

1 FADH2 = 2 ATP - Total of 4 ATP

*FADH2 and NADH ATP production occurs in the electron transport system 

Important Steps of the Krebs Cycle 1

Citrate Synthase

Important Steps of the Krebs Cycle 2

Isocitrate Dehydrogenase

Important Steps of the Krebs Cycle 3

alpha-ketoglutarate Dehydrogenase

Important Steps of the Krebs Cycle 4

Succinyl CoA Synthesase

Important Steps of the Krebs Cycle 5 

Succinate dehydronase

Important Steps of the Krebs Cycle 6

Malate Dehydrogenase

*The Electron Transport Chain (ETS) is coupled to the Krebs Cycle

*The hydrogen ions that are produced from glycolysis and the krebs cycle combine with NAD and FAD, forming NADH and FADH2

1) It prevents the build up of H+, thereby limiting acidification of the msucle and blood

2) Carries the H+ ion to the ETS where the H+ is passed through a series of reactions forming ATP

3) The H+ combines with oxygen to form water

*The ETC is in the inner membrane of the mitochondria

*Consists of four large protein complexes, and two smaller mobile carrier

*NADH and FADH2 are the electron donors

*The complexes pump protons from the matrix space of the mitochondria into the intermembrane space creating a proton gradient

*Protons travel through ATP synthase to create ATP

*Lypolysis- Breakdown of triglycerides into glycerol and free fatty accids

*FFAs travel via blood to muscle fibers and are broken down by enzymes in the mitochondria into acetic acid which is converted to acetl CoA (Beta oxidation)

*Acetyl CoA enters the Krebs cycle and the electron transport chain

*Fat oxidation requires more oxygen and generates more energy than carbohydrate oxidation

*Once Acetyl CoA enters the Krebs cycle, it follows the same fate as carbohydrate 2-carbon compounds which go through the ETS producing ATP, CO2, and H2O

*FFAs can produce much more ATP than can carbohydrate

*Requires 2 ATP to start beta-oxidation

*16 carbon fatty acid (palmitate) the overall reaction for one round of oxidation is (myristol CoA is palmitoyl CoA minus 2 carbons)

*Palmitoyl Coa+FAD+NAD+CoA+H2O=>Myristoyl CoA+FADH2+NADH+H++acetyl CoA

*Of course to completely degrade palmitoyl CoA would require 7 rounds of beta oxidation

*After the 7th round, you are left with an 8th acetyl CoA (CH2-CO-CoA)

*So the equation for the complete degradation of palmitate is :

Palmitoyl CoA+7FAD+7NAD+7CoA+7H2O=>8Acetyl CoA+7FAHD2+7NADH+7H+

*What is the ATP yield from oxidation of palmitate?

*Total number of ATP from 1 FFA molecule of palmitate: 117. (Will have to burn 2 for activation)

*The ATP-PCr and glycolytic systems produce small amounts of ATP anaerobically and are the major energy contributors in the early minutes of high-intensity exercise

*The oxidative system uses oxygen and produces more energy than the anaerobic systems

*Carbohydrate oxidation involves glycolysis, the Krebs cycle, and the electron transport chain to produce 39 ATP per molecule of glycogen

*Fat oxidation involves Beta-oxidation of FFA, the Krebs cycle, and the ETC to produce more ATP than carbohydrate

*Protein contributes little to energy production, and its oxidation is complex because amino acids contain nitrogen which cannot be oxidized

*The oxidative capacity of muscle fibers depends on their oxidative enzyme levels, fiber-type composition, how they have been trained, and oxygen availability