topic 2: bioenergetics 1, 2, 3 - exercise physiology

bioenergetics

converting energy from food stuffs into useable energy

• fats, carbs, proteins

• chemical energy into mechanical energy in the form of skeletal muscle contraction

  • chemical waste: CO2 and water

biochemical pathways

pathways that generate ATP for different activities

1) anaerobic metabolism: phosphocreatine + ADP → ATP (0-10 sec)

• ex: 100 m sprint, heavy lifting

2) anaerobic metabolism: glycolysis (glucose → ATP) (to 2 min)

• ex: 200-400 m run, high-rep lifting

3) aerobic metabolism: carbs, fats, proteins → ATP (30 min-hours)

• ex: endurance and long-distance

metabolism: small carbon chains → krebs cycle → ETC → ATP

atp

adenosine triphosphate consists of adenine, ribose, and three linked phosphates

• synthesis: energy is stored in ATP (ADP + Pi + energy → ATP)

• degradation/breakdown: energy is released (ATP —ATPase—> ADP + Pi + energy)

  • promotes muscle contraction, actin/myosin to bind

anaerobic metabolism

does not involve O2 in the generation of ATP

1) ATP-Pc system: phosphocreatine breakdown

2) glycolysis: from glucose or glycogen

ATP-Pc system

used as an immediate source of ATP up to 20 seconds of all-out effort that occurs within cytosol and with a single enzyme

• PCr formed at REST since it is used during activity

  • takes some energy to make PCr

• phosphocreatine + ADP —creatine kinase—> ATP + C

• substrate PCr is in cytosol, presence of the rate limiting enzyme creatine kinase breaks it down

  • this breakdown gives free energy

  • ADP also in cytosol

• three substrates from PCr: creatine, Pi, and free energy to generate ATP for the muscles

  • then free energy, Pi, ADP = ATP

• stimulated by ADP

• inhibited by ATP (when there is enough/abundance)

phosphocreatine

supplies inorganic phosphate and free energy that make up ATP

• increase stores by sleeping, creatine supplements, and training

• more phosphocreatine = more ATP for activity that uses ATP-Pc system

• ex: after depletion, typically 90 sec b/t sets but not fully replenished

creatine

binds with inorganic phosphate to form phosphocreatine controlled by creatine kinase enzyme

• moves phosphate inside muscle cell and help transfers phosphate back to ADP

• helps rebuilds PCr during rest for the system to work again

• supplements help b/c it takes some energy to form PCr: increases PCr stores to generate more ATP for short duration, high intensity exercise <3 min

glycolysis

the next pathway for ATP anaerobic production starting from glucose or glycogen

• aerobic: 2 pyruvate → acetyl CoA

• anaerobic: 2 pyruvate →← lactate

• rate limiting enzyme: phosphofructokinase

  • stimulated by ADP, Pi, and increase in pH

  • inhibited by ATP, citrate, decrease in pH

• ex: 400-800 m runs, intense weightlifting, sprinting in soccer

lactate vs lactic acid

lactate: normal byproduct from anaerobic metabolism to regenerate NAD+ by lactate dehydrogenase

• also makes a link from glycolysis to oxidative phosphorylation metabolism

• also can be a fuel source in aerobic metabolism

lactic acid: formed with lactate by adding an H+, and it cannot stay intact because the body’s environment is much less acidic

start from glucose

1) glucose → glucose 6-phosphate

• Pi from breakdown of ATP

• by hexokinase enzyme

• ATP invested

• phosphorylation

2) glucose 6 phosphate to fructose 6-phoshate

3) fructose 6-phosphate to fructose 1,6-diphosphate

• with Pi from breakdown of ATP

• by phosphofructokinase rate limiting enzyme

• ATP invested

4) fructose 1,6-diphosphate branches into 2 pathways, each generating 2 ATPs, 2 NADH, to 2 pyruvate

glucose ATP tally

invested 2 ATPs (hexokinase and phosphofructokinase enzymes made possible)

generating 4 ATPs

net: 2 ATPs

start from glycogen

1) glycogen → glucose 1-phosphate

2) glucose 1-phosphate to glucose 6-phosphate

3) glucose 6-phosphate to fructose 6-phoshate

• with Pi from breakdown of ATP

• by phosphofructokinase rate limiting enzyme

• ATP invested

4) fructose 6-phosphate to fructose 1,6-diphosphate

5) fructose 1,6-diphosphate branches into 2 pathways, each generating 2 ATPs, 2 NADH, to 2 pyruvate

• 4 ATP generated

glycogen ATP tally

investing 1 ATP (phosphofructokinase enzyme made possible)

generating 4 ATP

net: 3 ATPs

aerobic reconversion of NAD in glycolysis (aerobic NAD)

glycolysis → NADH + H+ → hydrogen shuttle

• NADH in mitochondria → hydrogen shuttle of mitochondrial membrane → H+ removed from NADH → ETC → oxidation → NAD+ returns to glycolysis

hydrogen shuttles

shuttles to move energy across inner mitochondrial membrane since NADH is impermeable

• regenerate NAD+ in cytosol and delivering electrons to ETC

• aerobic

1) glycerol 3-phosphate: transport NADH from glycolysis in skeletal muscle

2) malate-aspartate: transport NADH from glycolysis in organs of heart and liver

anaerobic reconversion of NAD in glycolysis (anaerobic NAD)

pyruvate in cytsosol —lactate dehydrogenase—> lactate

• NADH converted to NAD+ in cytosol→ H+ donated to lactate → NAD+ reconverted and returns to glycolysis

aerobic metabolism

in presence of oxygen, food substrates (carb, fats, proteins) are oxidized and generate ATP, followed by e-(H+) collection to make ATP

1) stage 1: broken down to simplest forms (glucose, fatty acids, amino acids) and generate acetyl- CoA

• three forms relate to be dumped into krebs cycle then to ETC, can all take the form acetyl CoA

2) stage 2: krebs cycle to oxidize actyl CoA — remove e- and collected by NAD and FAD to make NADH and FADH carriers

3) stage 3: NADHs and FADHS go through ETC to make ATP

• water and CO2 byproduct expelled from body by breathing

• ATP produced here is far greater than anaerobic metabolism

• carb ___ metabolism is just glycolysis

fats aerobic metabolism

triglycerides —lipolysis by lipase enzyme—> glycerol and free fatty acid → activated fatty acid —carnitine shuttle—> acyl CoA now in mitochondria

• —beta oxidation—> acetyl CoA (stage 1)

• carnitine shuttle: how an activated fatty acid is transported into mitochondria to make acyl CoA by acyl CoA synthase

protein metabolism

how a protein is broken down into amino acids (proteolysis) which then needs an amine group removed

• aerobic

1) transanimation: amine group added to a different carbon skeleton and makes new AA

2) deanimation: amine group removed and excreted as urine, deanimated and can enter the aerobic metabolism pathway

amino acid

can get into the krebs cycle by…

1) some can be used to synthesize glucose so they are glucogenic → glucose → pyruvate

2) some can be transformed into acetyl CoA

3) some can enter krebs cycle directly and are glucogenic

krebs cycle

the stage where acetyl CoA goes thru phases for electrons to get kicked off (oxidation)

• NAD+ or FAD+ picks up H+ → reduced to 3 NADH and 1 FADH → transported to ETC

  • FAD+ not present in glycolysis

• rate limiting enzyme: isocitrate dehydrogenase

  • produces: 2.5 ATP / NADH, 1.5 ATP /FADH, 1 GTP -> ATP

  • GTP broken down for cycle to keep going, drops a Pi to make ATP

• glycolysis -> 2 pyruvate -> 2 acetyl-CoA -> 2 turns in this cycle = 2 ATP

• total: 6 NADHs, 2 FADHs, and 2 ATPs

electron transport chain (ETC)

where NADHS and FADHS carry electrons to generate ATP, in the intermembrane space and mitochondrial matrix

• electrons passed from one area to another (protein pumps) losing energy as they pass

• release of energy pumps H+ from matrix to intermembrane space, making potential energy

• happens at the same time with oxidative phosphorylation

oxidative phosphorylation

where H+ is accumulated in intermembrane space and contains a lot of energy, driving the ATP synthase proton gradient to make ATP

• happens at the same time as the ETC

chemiosmotic hypothesis

electron carriers bring high-energy electrons to the ETC that power H+ pumping

NADHs: coming from glycolysis and krebs cycle enter the first complex of ETC

• NADHs donates e- and releases H+ → NAD+

• H+ forms the proton gradient in intermembrane space

• e- move along the complexes, binding to iron substrates, at each complex

• H+ pumped to intermembrane space

• NAD never leaves inner mitochondrial membrane

FADHs: coming from krebs cycle and enter at a later complex of ETC (fewer ATP produced)

• e- breaks off of H+, picked up by CoQ lipid carrier

• H+ pumped to intermembrane space

• FAD stays in matrix

cyt oxidase pump

the THIRD pump and rate limiting enzyme of ETC where oxygen is the final acceptor of electrons

• oxygen combines with low energy electrons and H+ = water

• pumps H+ from matrix into intermembrane space → ATP synthase proton gradient → ATP

  • ADP and Pi actively transported into matrix to make ATP

• removing electrons keep ETC running

ATP tally

2 net ATP generated from glucose/glycogen in glycolysis

• 2 NADHs delivered to ETC, 2.5 ATP per NADH = 5 ATP

2 pyruvate → 2 acetyl CoA

• 2 NADHs delivered, 2.5 ATP per NADH = 5 ATP

2 acetyl CoA → krebs cycle

• 6 NADH delivered to ETC, 2.5 per NADH = 15 ATP

• 2 FADH2 delivered to ETC, 1.5 ATP per FADH2 = 3 ATP

2 turns in krebs cycle → per turn: 2 ATP

= 30 ATP

glucose ATP tally

32 ATP generated when one glucose molecule undergoes aerobic metabolism

• 2 net ATP during glycolysis

glycogen ATP tally

 33 ATP generated when one glycogen molecule undergoes aerobic metabolism

• 3 net ATP during glycolysis