Ch 6 Energy Transfer in the Body

ATP recycling      

cells contain a small quantity of ATP (80-100g)

it must be resynth

2-3 s of max exercise

Energy transfers in the mitochondrion    

Citric acid cycle/respiratory chain (aerobic)

fatty acids

pyruvate from glucose

some deaminated amino acids

makes ATP —> biologic work   

energy transfers in cytosol

glycolysis (anaerobic)

phosphocreatine

glucose/glycogen

glycerol

some deaminated amino acids (BCAA)

Phosphocreatine (PCr)    

splitting of a phosphate from PCr

resynth ATP

4-6 times more PCr than ATP

max energy yield in about 10s

rarely fully depleted during exercise

15 sec max intensity can decrease PCr to    

about 5%    

Advanced possible functions of PCr   

Buffers H⁺

shuttles energy to high use areas

• greater diffusion rate

• link b/w mitochondria and cytosol

possible antioxidant

MtCK stabilizes mitochondria

oxidative phosphorylation    

synthesizes ATP by transferring electrons from NADH and FADH₂ to oxygen

generates H⁺ gradient b/w mitochondrial spaces

mechanical —> chemical energy via ATP synthase

_____% of ATP synthesis is from oxidative phosphorylation if possible   

90%

mitochondrial oxygen serves as the final electron _____    

acceptor

produces water

activity of oxidative phosphorylation requires   

1. tissue availability of NAD and FAD

   1. reason for creating lactate

2. oxygen present in the tissues

3. sufficient enzyme and mitochondrial concentration

**reduced rate of ATP synth if conditions are not met

Energy release from macronutrients: Stage 1   

digestion and absorption

large macromolecules —> smaller subunits

Energy release from macronutrients: stage 2   

amino acids, glucose, fatty acid, and glycerol units —> Acetyl coenzyme A    

Energy release from macronutrients: Stage 3   

Acetyl CoA degrades to CO₂ + H₂O + ATP

through Krebs and ETC

#1 fuel source   

PCr and ATP within cell    

#2 fuel source   

muscle glycogen

+ triacylglycerol —> blood glucose

#3 fuel source   

liver glycogen

broken down and transported as glucose    

#4 fuel source   

FFA

from triacylglycerols in liver and adipocytes

#5 fuel source

liver: deaminated amino acids

carbon skeletons

1 mol glucose =    

686 kcal of available energy

complete breakdown using oxidation

remaining energy dissipates as heat

anaerobic glycolysis   

pyruvate to lactate

releases 5% of the energy from glucose    

aerobic glycolysis

pyruvate to Acetyl-CoA

• citric acid cycle

• ETC

releases the rest of energy (+95%)

• some lost as heat

rapid (anaerobic) glycolysis depends on   

glycolytic enzymes

• hexokinase

• pyruvate kinase

• phosphofructokinase

• fructose 1,6-diphosphate

rapid glycolysis forms  

lactate and +2 ATP total

occurs w/o O₂

oxygen abundance inhibits rapid glycolysis

substrate-level phosphorylation   

stores chemical energy in phosphate bond

transferred from substrate to ADP

30% efficiency

As exercise progresses, we start using this lipid source first

Triacylglycerols stored directly in muscle    

As exercise progresses, we start using this lipid source second    

circulating triacylglycerols in lipoprotein complexes

more FFA bound to albumin

As exercise progresses, we start using this lipid source third   

circulating FFA from adipose tissue

first broken down from TAGs

Most triacyl glycerides are stored within   

a fat cell    

adipocytes   

high energy storage capacity

hormone-sensitive lipase   

stimulates triacylglycerol breakdown in the adipocyte cell

glycerol and 3 fatty acids

free fatty acids transported via

bound to albumin    

energy depends on the number of ____ in the fatty acid   

number of carbons

18-carbon fatty acid molecule produces   

+147 molecules of ATP

beta-oxidation and citric acid cycle metabolism

• each triacylglycerol contains 3 fatty acid

  • 3 × 147 = +441 ATP + 19 ATP from glycerol = 460 ATP total

6 steps to mobilize FFA

1. breakdown TAGs for FFA

2. transport FFA in blood

3. uptake FFA to muscle cell

4. entry of activated fatty acid into muscle mitochondria

5. breakdown of fatty acid to acetyl-CoA via beta-oxidation

6. coupled oxidation in krebs cycle and ETC

hormonal effects on lipid catabolism    

lipase activation mobilizes free fatty acids from adipose tissue caused by

1. epinephrine

2. norepinephrine

3. glucagon

4. growth hormone (increases use of fat, decr carb use)

lipogenesis   

carbs convert to lipids (also to nonessential a.a.)

lipids predominantly interconvert to   

nonessential amino acids    

proteins predominantly interconvert into    

carbs or lipids

energy release from protein   

after deamination, carbon skeleton enters metabolic pathways

deamination produces intermediates for glucose synth. (glucogenic amino acids)

deamination produces intermediates for acetyl-CoA for TAG formation (ketogenic a.a.)